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  • Joseph Nebus 6:00 pm on Thursday, 9 February, 2017 Permalink | Reply
    Tags: arithmetic, , , Dogs of C Kennel, , , , Nest Heads, One Big Happy   

    Reading the Comics, February 3, 2017: Counting Edition 


    And now I can close out last week’s mathematically-themed comic strips. Two of them are even about counting, which is enough for me to make that the name of this set.

    John Allen’s Nest Heads for the 2nd mentions a probability and statistics class and something it’s supposed to be good for. I would agree that probability and statistics are probably (I can’t find a better way to write this) the most practically useful mathematics one can learn. At least once you’re past arithmetic. They’re practical by birth; humans began studying them because they offer guidance in uncertain situations. And one can use many of their tools without needing more than arithmetic.

    I’m not so staunchly anti-lottery as many mathematics people are. I’ll admit I play it myself, when the jackpot is large enough. When the expectation value of the prize gets to be positive, it’s harder to rationalize not playing. This happens only once or twice a year, but it’s fun to watch and see when it happens. I grant it’s a foolish way to use two dollars (two tickets are my limit), but you know? My budget is not so tight I can’t spend four dollars foolishly a year. Besides, I don’t insist on winning one of those half-billion-dollar prizes. I imagine I’d be satisfied if I brought in a mere $10,000.

    'Hey, Ruthie's Granny, how old are you?' 'You can't count that high, James.' 'I can too!' 'Fine! Start at one and I'll tell you when you get to my age.' '1, 2, 3, 4, 11, 22, 88, 99, 200, a gazillion!' 'Very good! It's somewhere between 22 and a gazillion!' 'Gazowie!'

    Rick Detorie’s One Big Happy for the 3rd of February, 2017. A ‘gazillion’ is actually a surprisingly low number, hovering as it does somewhere around 212. Fun fact!

    Rick Detorie’s One Big Happy for the 3rd continues my previous essay’s bit of incompetence at basic mathematics, here, counting. But working out that her age is between 22 an a gazillion may be worth doing. It’s a common mathematical challenge to find a correct number starting from little information about it. Usually we find it by locating bounds: the number must be larger than this and smaller than that. And then get the bounds closer together. Stop when they’re close enough for our needs, if we’re numerical mathematicians. Stop when the bounds are equal to each other, if we’re analytic mathematicians. That can take a lot of work. Many problems in number theory amount to “improve our estimate of the lowest (or highest) number for which this is true”. We have to start somewhere.

    Samson’s Dark Side of the Horse for the 3rd is a counting-sheep joke and I was amused that the counting went so awry here. On looking over the strip again for this essay, though, I realize I read it wrong. It’s the fences that are getting counted, not the sheep. Well, it’s a cute little sheep having the same problems counting that Horace has. We don’t tend to do well counting more than around seven things at a glance. We can get a bit farther if we can group things together and spot that, say, we have four groups of four fences each. That works and it’s legitimate; we’re counting and we get the right count out of it. But it does feel like we’re doing something different from how we count, say, three things at a glance.

    Mick Mastroianni and Mason MastroianniDogs of C Kennel for the 3rd is about the world’s favorite piece of statistical mechanics, entropy. There’s room for quibbling about what exactly we mean by thermodynamics saying all matter is slowly breaking down. But the gist is fair enough. It’s still mysterious, though. To say that the disorder of things is always increasing forces us to think about what we mean by disorder. It’s easy to think we have an idea what we mean by it. It’s hard to make that a completely satisfying definition. In this way it’s much like randomness, which is another idea often treated as the same as disorder.

    Bill Amend’s FoxTrot Classics for the 3rd reprinted the comic from the 10th of February, 2006. Mathematics teachers always want to see how you get your answers. Why? … Well, there are different categories of mistakes someone can make. One can set out trying to solve the wrong problem. One can set out trying to solve the right problem in a wrong way. One can set out solving the right problem in the right way and get lost somewhere in the process. Or one can be doing just fine and somewhere along the line change an addition to a subtraction and get what looks like the wrong answer. Each of these is a different kind of mistake. Knowing what kinds of mistakes people make is key to helping them not make these mistakes. They can get on to making more exciting mistakes.

     
  • Joseph Nebus 6:00 pm on Sunday, 5 February, 2017 Permalink | Reply
    Tags: , , arithmetic, , , , Pajama Diaries, ,   

    Reading the Comics, February 2, 2017: I Haven’t Got A Jumble Replacement Source Yet 


    If there was one major theme for this week it was my confidence that there must be another source of Jumble strips out there. I haven’t found it, but I admit not making it a priority either. The official Jumble site says I can play if I activate Flash, but I don’t have enough days in the year to keep up with Flash updates. And that doesn’t help me posting mathematics-relevant puzzles here anyway.

    Mark Anderson’s Andertoons for January 29th satisfies my Andertoons need for this week. And it name-drops the one bit of geometry everyone remembers. To be dour and humorless about it, though, I don’t think one could likely apply the Pythagorean Theorem. Typically the horizontal axis and the vertical axis in a graph like this measure different things. Squaring the different kinds of quantities and adding them together wouldn’t mean anything intelligible. What would even be the square root of (say) a squared-dollars-plus-squared-weeks? This is something one learns from dimensional analysis, a corner of mathematics I’ve thought about writing about some. I admit this particular insight isn’t deep, but everything starts somewhere.

    Norm Feuti’s Gil rerun for the 30th is a geometry name-drop, listing it as the sort of category Jeopardy! features. Gil shouldn’t quit so soon. The responses for the category are “What is the Pythagorean Theorem?”, “What is acute?”, “What is parallel?”, “What is 180 degrees?” (or, possibly, 360 or 90 degrees), and “What is a pentagon?”.

    Parents' Glossary Of Terms: 'Mortifraction': That utter shame when you realize you can no longer do math in your head. Parent having trouble making change at a volunteer event.

    Terri Libenson’s Pajama Diaries for the 1st of February, 2017. You know even for a fundraising event $17.50 seems a bit much for a hot dog and bottled water. Maybe the friend’s 8-year-old child is way off too.

    Terri Libenson’s Pajama Diaries for the 1st of February shows off the other major theme of this past week, which was busy enough that I have to again split the comics post into two pieces. That theme is people getting basic mathematics wrong. Mostly counting. (You’ll see.) I know there’s no controlling what people feel embarrassed about. But I think it’s unfair to conclude you “can no longer” do mathematics in your head because you’re not able to make change right away. It’s normal to be slow or unreliable about something you don’t do often. Inexperience and inability are not the same thing, and it’s unfair to people to conflate them.

    Gordon Bess’s Redeye for the 21st of September, 1970, got rerun the 1st of February. And it’s another in the theme of people getting basic mathematics wrong. And even more basic mathematics this time. There’s more problems-with-counting comics coming when I finish the comics from the past week.

    'That was his sixth shot!' 'Good! OK, Paleface! You've had it now!' (BLAM) 'I could never get that straight, does six come after four or after five?'

    Gordon Bess’s Redeye for the 21st of September, 1970. Rerun the 1st of February, 2017. I don’t see why they’re so worried about counting bullets if being shot just leaves you a little discombobulated.

    Dave Whamond’s Reality Check for the 1st hopes that you won’t notice the label on the door is painted backwards. Just saying. It’s an easy joke to make about algebra, also, that it should put letters in to perfectly good mathematics. Letters are used for good reasons, though. We’ve always wanted to work out the value of numbers we only know descriptions of. But it’s way too wordy to use the whole description of the number every time we might speak of it. Before we started using letters we could use placeholder names like “re”, meaning “thing” (as in “thing we want to calculate”). That works fine, although it crashes horribly when we want to track two or three things at once. It’s hard to find words that are decently noncommittal about their values but that we aren’t going to confuse with each other.

    So the alphabet works great for this. An individual letter doesn’t suggest any particular number, as long as we pretend ‘O’ and ‘I’ and ‘l’ don’t look like they do. But we also haven’t got any problem telling ‘x’ from ‘y’ unless our handwriting is bad. They’re quick to write and to say aloud, and they don’t require learning to write any new symbols.

    Later, yes, letters do start picking up connotations. And sometimes we need more letters than the Roman alphabet allows. So we import from the Greek alphabet the letters that look different from their Roman analogues. That’s a bit exotic. But at least in a Western-European-based culture they aren’t completely novel. Mathematicians aren’t really trying to make this hard because, after all, they’re the ones who have to deal with the hard parts.

    Bu Fisher’s Mutt and Jeff rerun for the 2nd is another of the basic-mathematics-wrong jokes. But it does get there by throwing out a baffling set of story-problem-starter points. Particularly interesting to me is Jeff’s protest in the first panel that they couldn’t have been doing 60 miles an hour as they hadn’t been out an hour. It’s the sort of protest easy to use as introduction to the ideas of average speed and instantaneous speed and, from that, derivatives.

     
  • Joseph Nebus 6:00 pm on Sunday, 29 January, 2017 Permalink | Reply
    Tags: arithmetic, , Committed, , , Frog Applause, , Randy Glasbergen, , TruthFacts   

    Reading the Comics, January 28, 2017: Chuckle Brothers Edition 


    The week started out quite busy and I was expecting I’d have to split my essay again. It didn’t turn out that way; Comic Strip Master Command called a big break on mathematically-themed comics from Tuesday on. And then nobody from Comics Kingdom or from Creators.com needed inclusion either. I just have a bunch of GoComics links and a heap of text here. I bet that changes by next week. Still no new Jumble strips.

    Brian Boychuk and Ron Boychuk’s The Chuckle Brothers for the 22nd was their first anthropomorphic numerals joke of the week.

    Kevin Fagan’s Drabble for the 22nd uses arithmetic as the sort of problem it’s easy to get clearly right or clearly wrong. It’s a more economical use of space than (say) knowing how many moons Saturn’s known to have. (More than we thought there were as long ago as Thursday.) I do like that there’s a decent moral to this on the way to the punch line.

    Bill Amend’s FoxTrot for the 22nd has Jason stand up for “torus” as a better name for doughnuts. You know how nerdy people will like putting a complicated word onto an ordinary thing. But there are always complications. A torus ordinarily describes the shape made by rotating a circle around an axis that’s in the plane of the circle. The result is a surface, though, the shell of a doughnut and none of the interior. If we’re being fussy. I don’t know of a particular name for the torus with its interior and suspect that, if pressed, a mathematician would just say “torus” or maybe “doughnut”.

    We can talk about toruses in two dimensions; those look just like circles. The doughnut-shell shape is a torus in three dimensions. There’s torus shapes made by rotating spheres, or hyperspheres, in four or more dimensions. I’m not going to draw them. And we can also talk about toruses by the number of holes that go through them. If a normal torus is the shape of a ring-shaped pool toy, a double torus is the shape of a two-seater pool toy, a triple torus something I don’t imagine exists in the real world. A quadruple torus could look, I imagine, like some pool toys Roller Coaster Tycoon allows in its water parks. I’m saying nothing about whether they’re edible.

    Brian Boychuk and Ron Boychuk’s The Chuckle Brothers for the 23rd was their second anthropomorphic numerals joke of the week. I suppose sometimes you just get an idea going.

    Mikael Wulff and Anders Morgenthaler’s TruthFacts for the 23rd jokes about mathematics skills versus life. The growth is fine enough; after all, most of us are at, or get to, our best at something while we’re training in it or making regular use of it. So the joke peters out into the usual “I never use mathematics in real life” crack, which, eh. I agree it’s what I feel like my mathematics skills have done ever since I got my degree, at any rate.

    Teresa Burritt’s Frog Applause for the 24th describes an extreme condition which hasn’t been a problem for me. I’m not an overindulgey type.

    Randy Glasbergen’s Glasbergen Cartoons rerun for the 26th is the pie chart joke for this week.

    Michael Fry’s Committed rerun for the 28th just riffs on the escalation of hyperbole, and what sure looks like an exponential growth of hyperbolic numbers. There’s a bit of scientific notation in the last panel. The “1 x” part isn’t necessary. It doesn’t change the value of the expression “1 x 1026”. But it might be convenient to use the “1 x” anyway. Scientific notation is about separating the size of the number from the interesting digits that the number has. Often when you compare numbers you’re interested in the size or else you’re interested in the important digits. Get into that habit and it’s not worth making an exception just because the interesting digits turn out to be boring in this case.

     
  • Joseph Nebus 6:00 pm on Sunday, 15 January, 2017 Permalink | Reply
    Tags: arithmetic, Barkeater Lake, combinatorics, , Dinette Set, Dinosaur Comics, Nancy, , Reply All, , Slylock Fox,   

    Reading the Comics, January 14, 2017: Redeye and Reruns Edition 


    So for all I worried about the Gocomics.com redesign it’s not bad. The biggest change is it’s removed a side panel and given the space over to the comics. And while it does show comics you haven’t been reading, it only shows one per day. One week in it apparently sticks with the same comic unless you choose to dismiss that. So I’ve had it showing me The Comic Strip That Has A Finale Every Day as a strip I’m not “reading”. I’m delighted how thisbreaks the logic about what it means to “not read” an “ongoing comic strip”. (That strip was a Super-Fun-Pak Comix offering, as part of Ruben Bolling’s Tom the Dancing Bug. It was turned into a regular Gocomics.com feature by someone who got the joke.)

    Comic Strip Master Command responded to the change by sending out a lot of comic strips. I’m going to have to divide this week’s entry into two pieces. There’s not deep things to say about most of these comics, but I’ll make do, surely.

    Julie Larson’s Dinette Set rerun for the 8th is about one of the great uses of combinatorics. That use is working out how the number of possible things compares to the number of things there are. What’s always staggering is that the number of possible things grows so very very fast. Here one of Larson’s characters claims a science-type show made an assertion about the number of possible ideas a brain could hold. I don’t know if that’s inspired by some actual bit of pop science. I can imagine someone trying to estimate the number of possible states a brain might have.

    And that has to be larger than the number of atoms in the universe. Consider: there’s something less than a googol of atoms in the universe. But a person can certainly have the idea of the number 1, or the idea of the number 2, or the idea of the number 3, or so on. I admit a certain sameness seems to exist between the ideas of the numbers 2,038,412,562,593,604 and 2,038,412,582,593,604. But there is a difference. We can out-number the atoms in the universe even before we consider ideas like rabbits or liberal democracy or jellybeans or board games. The universe never had a chance.

    Or did it? Is it possible for a number to be too big for the human brain to ponder? If there are more digits in the number than there are atoms in the universe we can’t form any discrete representation of it, after all. … Except that we kind of can. For example, “the largest prime number less than one googolplex” is perfectly understandable. We can’t write it out in digits, I think. But you now have thought of that number, and while you may not know what its millionth decimal digit is, you also have no reason to care what that digit is. This is stepping into the troubled waters of algorithmic complexity.

    Shady Shrew is selling fancy bubble-making wands. Shady says the crazy-shaped wands cost more than the ordinary ones because of the crazy-shaped bubbles they create. Even though Slylock Fox has enough money to buy an expensive wand, he bought the cheaper one for Max Mouse. Why?

    Bob Weber Jr’s Slylock Fox and Comics for Kids for the 9th of January, 2017. Not sure why Shady Shrew is selling the circular wands at 50 cents. Sure, I understand wanting a triangle or star or other wand selling at a premium. But then why have the circular wands at such a cheap price? Wouldn’t it be better to put them at like six dollars, so that eight dollars for a fancy wand doesn’t seem that great an extravagance? You have to consider setting an appropriate anchor point for your customer base. But, then, Shady Shrew isn’t supposed to be that smart.

    Bob Weber Jr’s Slylock Fox and Comics for Kids for the 9th is built on soap bubbles. The link between the wand and the soap bubble vanishes quickly once the bubble breaks loose of the wand. But soap films that keep adhered to the wand or mesh can be quite strangely shaped. Soap films are a practical example of a kind of partial differential equations problem. Partial differential equations often appear when we want to talk about shapes and surfaces and materials that tug or deform the material near them. The shape of a soap bubble will be the one that minimizes the torsion stresses of the bubble’s surface. It’s a challenge to solve analytically. It’s still a good challenge to solve numerically. But you can do that most wonderful of things and solve a differential equation experimentally, if you must. It’s old-fashioned. The computer tools to do this have gotten so common it’s hard to justify going to the engineering lab and getting soapy water all over a mathematician’s fingers. But the option is there.

    Gordon Bess’s Redeye rerun from the 28th of August, 1970, is one of a string of confused-student jokes. (The strip had a Generic Comedic Western Indian setting, putting it in the vein of Hagar the Horrible and other comic-anachronism comics.) But I wonder if there are kids baffled by numbers getting made several different ways. Experience with recipes and assembly instructions and the like might train someone to thinking there’s one correct way to make something. That could build a bad intuition about what additions can work.

    'I'm never going to learn anything with Redeye as my teacher! Yesterday he told me that four and one make five! Today he said, *two* and *three* make five!'

    Gordon Bess’s Redeye rerun from the 28th of August, 1970. Reprinted the 9th of January, 2017. What makes the strip work is how it’s tied to the personalities of these kids and couldn’t be transplanted into every other comic strip with two kids in it.

    Corey Pandolph’s Barkeater Lake rerun for the 9th just name-drops algebra. And that as a word that starts with the “alj” sound. So far as I’m aware there’s not a clear etymological link between Algeria and algebra, despite both being modified Arabic words. Algebra comes from “al-jabr”, about reuniting broken things. Algeria comes from Algiers, which Wikipedia says derives from `al-jaza’ir”, “the Islands [of the Mazghanna tribe]”.

    Guy Gilchrist’s Nancy for the 9th is another mathematics-cameo strip. But it was also the first strip I ran across this week that mentioned mathematics and wasn’t a rerun. I’ll take it.

    Donna A Lewis’s Reply All for the 9th has Lizzie accuse her boyfriend of cheating by using mathematics in Scrabble. He seems to just be counting tiles, though. I think Lizzie suspects something like Blackjack card-counting is going on. Since there are only so many of each letter available knowing just how many tiles remain could maybe offer some guidance how to play? But I don’t see how. In Blackjack a player gets to decide whether to take more cards or not. Counting cards can suggest whether it’s more likely or less likely that another card will make the player or dealer bust. Scrabble doesn’t offer that choice. One has to refill up to seven tiles until the tile bag hasn’t got enough left. Perhaps I’m overlooking something; I haven’t played much Scrabble since I was a kid.

    Perhaps we can take the strip as portraying the folk belief that mathematicians get to know secret, barely-explainable advantages on ordinary folks. That itself reflects a folk belief that experts of any kind are endowed with vaguely cheating knowledge. I’ll admit being able to go up to a blackboard and write with confidence a bunch of integrals feels a bit like magic. This doesn’t help with Scrabble.

    'Want me to teach you how to add and subtract, Pokey?' 'Sure!' 'Okay ... if you had four cookies and I asked you for two, how many would you have left?' 'I'd still have four!'

    Gordon Bess’s Redeye rerun from the 29th of August, 1970. Reprinted the 10th of January, 2017. To be less snarky, I do like the simply-expressed weariness on the girl’s face. It’s hard to communicate feelings with few pen strokes.

    Gordon Bess’s Redeye continued the confused-student thread on the 29th of August, 1970. This one’s a much older joke about resisting word problems.

    Ryan North’s Dinosaur Comics rerun for the 10th talks about multiverses. If we allow there to be infinitely many possible universes that would suggest infinitely many different Shakespeares writing enormously many variations of everything. It’s an interesting variant on the monkeys-at-typewriters problem. I noticed how T-Rex put Shakespeare at typewriters too. That’ll have many of the same practical problems as monkeys-at-typewriters do, though. There’ll be a lot of variations that are just a few words or a trivial scene different from what we have, for example. Or there’ll be variants that are completely uninteresting, or so different we can barely recognize them as relevant. And that’s if it’s actually possible for there to be an alternate universe with Shakespeare writing his plays differently. That seems like it should be possible, but we lack evidence that it is.

     
  • Joseph Nebus 6:00 pm on Friday, 9 December, 2016 Permalink | Reply
    Tags: , arithmetic, , evens, , , normal subgroups, odds,   

    The End 2016 Mathematics A To Z: Quotient Groups 


    I’ve got another request today, from the ever-interested and group-theory-minded gaurish. It’s another inspirational one.

    Quotient Groups.

    We all know about even and odd numbers. We don’t have to think about them. That’s why it’s worth discussing them some.

    We do know what they are, though. The integers — whole numbers, positive and negative — we can split into two sets. One of them is the even numbers, two and four and eight and twelve. Zero, negative two, negative six, negative 2,038. The other is the odd numbers, one and three and nine. Negative five, negative nine, negative one.

    What do we know about numbers, if all we look at is whether numbers are even or odd? Well, we know every integer is either an odd or an even number. It’s not both; it’s not neither.

    We know that if we start with an even number, its negative is also an even number. If we start with an odd number, its negative is also an odd number.

    We know that if we start with a number, even or odd, and add to it its negative then we get an even number. A specific number, too: zero. And that zero is interesting because any number plus zero is that same original number.

    We know we can add odds or evens together. An even number plus an even number will be an even number. An odd number plus an odd number is an even number. An odd number plus an even number is an odd number. And subtraction is the same as addition, by these lights. One number minus an other number is just one number plus negative the other number. So even minus even is even. Odd minus odd is even. Odd minus even is odd.

    We can pluck out some of the even and odd numbers as representative of these sets. We don’t want to deal with big numbers, nor do we want to deal with negative numbers if we don’t have to. So take ‘0’ as representative of the even numbers. ‘1’ as representative of the odd numbers. 0 + 0 is 0. 0 + 1 is 1. 1 + 0 is 1. The addition is the same thing we would do with the original set of integers. 1 + 1 would be 2, which is one of the even numbers, which we represent with 0. So 1 + 1 is 0. If we’ve picked out just these two numbers each is the minus of itself: 0 – 0 is 0 + 0. 1 – 1 is 1 + 1. All that gives us 0, like we should expect.

    Two paragraphs back I said something that’s obvious, but deserves attention anyway. An even plus an even is an even number. You can’t get an odd number out of it. An odd plus an odd is an even number. You can’t get an odd number out of it. There’s something fundamentally different between the even and the odd numbers.

    And now, kindly reader, you’ve learned quotient groups.

    OK, I’ll do some backfilling. It starts with groups. A group is the most skeletal cartoon of arithmetic. It’s a set of things and some operation that works like addition. The thing-like-addition has to work on pairs of things in your set, and it has to give something else in the set. There has to be a zero, something you can add to anything without changing it. We call that the identity, or the additive identity, because it doesn’t change something else’s identity. It makes sense if you don’t stare at it too hard. Everything has an additive inverse. That is everything has a “minus”, that you can add to it to get zero.

    With odd and even numbers the set of things is the integers. The thing-like-addition is, well, addition. I said groups were based on how normal arithmetic works, right?

    And then you need a subgroup. A subgroup is … well, it’s a subset of the original group that’s itself a group. It has to use the same addition the original group does. The even numbers are such a subgroup of the integers. Formally they make something called a “normal subgroup”, which is a little too much for me to explain right now. If your addition works like it does for normal numbers, that is, “a + b” is the same thing as “b + a”, then all your subgroups are normal groups. Yes, it can happen that they’re not. If the addition is something like rotations in three-dimensional space, or swapping the order of things, then the order you “add” things in matters.

    We make a quotient group by … OK, this isn’t going to sound like anything. It’s a group, though, like the name says. It uses the same addition that the original group does. Its set, though, that’s itself made up of sets. One of the sets is the normal subgroup. That’s the easy part.

    Then there’s something called cosets. You make a coset by picking something from the original group and adding it to everything in the subgroup. If the thing you pick was from the original subgroup that’s just going to be the subgroup again. If you pick something outside the original subgroup then you’ll get some other set.

    Starting from the subgroup of even numbers there’s not a lot to do. You can get the even numbers and you get the odd numbers. Doesn’t seem like much. We can do otherwise though. Suppose we start from the subgroup of numbers divisible by 4, though. That’s 0, 4, 8, 12, -4, -8, -12, and so on. Now there’s three cosets we can make from that. We can start with the original set of numbers. Or we have 1 plus that set: 1, 5, 9, 13, -3, -7, -11, and so on. Or we have 2 plus that set: 2, 6, 10, 14, -2, -6, -10, and so on. Or we have 3 plus that set: 3, 7, 11, 15, -1, -5, -9, and so on. None of these others are subgroups, which is why we don’t call them subgroups. We call them cosets.

    These collections of cosets, though, they’re the pieces of a new group. The quotient group. One of them, the normal subgroup you started with, is the identity, the thing that’s as good as zero. And you can “add” the cosets together, in just the same way you can add “odd plus odd” or “odd plus even” or “even plus even”.

    For example. Let me start with the numbers divisible by 4. I will have so much a better time if I give this a name. I’ll pick ‘Q’. This is because, you know, quarters, quartet, quadrilateral, this all sounds like four-y stuff. The integers — the integers have a couple of names. ‘I’, ‘J’, and ‘Z’ are the most common ones. We get ‘Z’ from German; a lot of important group theory was done by German-speaking mathematicians. I’m used to it so I’ll stick with that. The quotient group ‘Z / Q’, read “Z modulo Q”, has (it happens) four cosets. One of them is Q. One of them is “1 + Q”, that set 1, 5, 9, and so on. Another of them is “2 + Q”, that set 2, 6, 10, and so on. And the last is “3 + Q”, that set 3, 7, 11, and so on.

    And you can add them together. 1 + Q plus 1 + Q turns out to be 2 + Q. Try it out, you’ll see. 1 + Q plus 2 + Q turns out to be 3 + Q. 2 + Q plus 2 + Q is Q again.

    The quotient group uses the same addition as the original group. But it doesn’t add together elements of the original group, or even of the normal subgroup. It adds together sets made from the normal subgroup. We’ll denote them using some form that looks like “a + N”, or maybe “a N”, if ‘N’ was the normal subgroup and ‘a’ something that wasn’t in it. (Sometimes it’s more convenient writing the group operation like it was multiplication, because we do that by not writing anything at all, which saves us from writing stuff.)

    If we’re comfortable with the idea that “odd plus odd is even” and “even plus odd is odd” then we should be comfortable with adding together quotient groups. We’re not, not without practice, but that’s all right. In the Introduction To Not That Kind Of Algebra course mathematics majors take they get a lot of practice, just in time to be thrown into rings.

    Quotient groups land on the mathematics major as a baffling thing. They don’t actually turn up things from the original group. And they lead into important theorems. But to an undergraduate they all look like text huddling up to ladders of quotient groups. We’re told these are important theorems and they are. They also go along with beautiful diagrams of how these quotient groups relate to each other. But they’re hard going. It’s tough finding good examples and almost impossible to explain what a question is. It comes as a relief to be thrown into rings. By the time we come back around to quotient groups we’ve usually had enough time to get used to the idea that they don’t seem so hard.

    Really, looking at odds and evens, they shouldn’t be so hard.

     
    • gaurish 9:10 am on Saturday, 10 December, 2016 Permalink | Reply

      Thanks! When I first learnt about quotient groups (two years ago) I visualized them as the equivalence classes we create so as to have a better understanding of a bigger group (since my study of algebra has been motivated by its need in Number theory as a generalization of modulo arithmetic). Then the isomorphism theorems just changed the way I look at quotient of an algebraic structure. See: http://math.stackexchange.com/q/1816921/214604

      Like

      • Joseph Nebus 5:47 am on Saturday, 17 December, 2016 Permalink | Reply

        I’m glad that you liked. I do think equivalence classes are the easiest way into quotient groups — it’s essentially what I did here — but that’s because people get introduced to equivalence classes without knowing what they are. Odd and even numbers, for example, or checking arithmetic by casting out nines are making use of these classes. Isomorphism theorems are great and substantial but they do take so much preparation to get used to. Probably shifting from the first to the second is the sign of really mastering the idea of a quotient group.

        Liked by 1 person

  • Joseph Nebus 6:00 pm on Sunday, 13 November, 2016 Permalink | Reply
    Tags: , arithmetic, complexity, , , , , ,   

    Reading the Comics, November 12, 2016: Frazz and Monkeys Edition 


    Two things made repeat appearances in the mathematically-themed comics this week. They’re the comic strip Frazz and the idea of having infinitely many monkeys typing. Well, silly answers to word problems also turned up, but that’s hard to say many different things about. Here’s what I make the week in comics out to be.

    'An infinite number of monkeys sitting at an infinite number of typewriters will eventually reproduce the works of Shakespeare. ... Justy sayin' ... a four digit pin number is statistically sooo much better.'

    Sandra Bell-Lundy’s Between Friends for the 6th of November, 2016. I’m surprised Bell-Lundy used the broader space of a Sunday strip for a joke that doesn’t need that much illustration, but I understand sometimes you just have to go with the joke that you have. And it isn’t as though Sunday comics get that much space anymore either. Anyway, I suppose we have all been there, although for me that’s more often because I used to have a six-digit pin, and a six-digit library card pin, and those were just close enough to each other that I could never convince myself I was remembering the right one in context, so I would guess wrong.

    Sandra Bell-Lundy’s Between Friends for the 6th introduces the infinite monkeys problem. I wonder sometimes why the monkeys-on-typewriters thing has so caught the public imagination. And then I remember it encourages us to stare directly into infinity and its intuition-destroying nature from the comfortable furniture of the mundane — typewriters, or keyboards, for goodness’ sake — with that childish comic dose of monkeys. Given that it’s a wonder we ever talk about anything else, really.

    Monkeys writing Shakespeare has for over a century stood as a marker for what’s possible but incredibly improbable. I haven’t seen it compared to finding a four-digit PIN. It has got me wondering about the chance that four randomly picked letters will be a legitimate English word. I’m sure the chance is more than the one-in-a-thousand chance someone would guess a randomly drawn PIN correctly on one try. More than one in a hundred? I’m less sure. The easy-to-imagine thing to do is set a computer to try out all 456,976 possible sets of four letters and check them against a dictionary. The number of hits divided by the number of possibilities would be the chance of drawing a legitimate word. If I had a less capable computer, or were checking even longer words, I might instead draw some set number of words, never minding that I didn’t get every possibility. The fraction of successful words in my sample would be something close to the chance of drawing any legitimate word.

    If I thought a little deeper about the problem, though, I’d just count how many four-letter words are already in my dictionary and divide that into 456,976. It’s always a mistake to start programming before you’ve thought the problem out. The trouble is not being able to tell when that thinking-out is done.

    Richard Thompson’s Poor Richard’s Almanac for the 7th is the other comic strip to mention infinite monkeys. Well, chimpanzees in this case. But for the mathematical problem they’re not different. I’ve featured this particular strip before. But I’m a Thompson fan. And goodness but look at the face on the T S Eliot fan in the lower left corner there.

    Jeff Mallet’s Frazz for the 6th gives Caulfield one of those flashes of insight that seems like it should be something but doesn’t mean much. He’s had several of these lately, as mentioned here last week. As before this is a fun discovery about Roman Numerals, but it doesn’t seem like it leads to much. Perhaps a discussion of how the subtractive principle — that you can write “four” as “IV” instead of “IIII” — evolved over time. But then there isn’t much point to learning Roman Numerals at all. It’s got some value in showing how much mathematics depends on culture. Not just that stuff can be expressed in different ways, but that those different expressions make different things easier or harder to do. But I suspect that isn’t the objective of lessons about Roman Numerals.

    Frazz got my attention again the 12th. This time it just uses arithmetic, and a real bear of an arithmetic problem, as signifier for “a big pile of hard work”. This particular problem would be — well, I have to call it tedious, rather than hard. doing it is just a long string of adding together two numbers. But to do that over and over, by my count, at least 47 times for this one problem? Hardly any point to doing that much for one result.

    Patrick Roberts’s Todd the Dinosaur for the 7th calls out fractions, and arithmetic generally, as the stuff that ruins a child’s dreams. (Well, a dinosaur child’s dreams.) Still, it’s nice to see someone reminding mathematicians that a lot of their field is mostly used by accountants. Actuaries we know about; mathematics departments like to point out that majors can get jobs as actuaries. I don’t know of anyone I went to school with who chose to become one or expressed a desire to be an actuary. But I admit not asking either.

    Todd declares that after hearing one speak to his class he wants to be an accountant when he grows up. Trent, Todd's caretaker, says that's great but he'll need to do stuff that involves 'carrying the one and probably some fractions.' Todd panics. 'AAAGH! Not 'carrying the one' and that other word you said!'

    Patrick Roberts’s Todd the Dinosaur for the 7th of November, 2016. I don’t remember being talked to by classmates’ parents about what they where, but that might just be that it’s been a long time since I was in elementary school and everybody had the normal sorts of jobs that kids don’t understand. I guess we talked about what our parents did but that should make a weaker impression.

    Mike Thompson’s Grand Avenue started off a week of students-resisting-the-test-question jokes on the 7th. Most of them are hoary old word problem jokes. But, hey, I signed up to talk about it when a comic strip touches a mathematics topic and word problems do count.

    Zach Weinersmith’s Saturday Morning Breakfast Cereal reprinted the 7th is a higher level of mathematical joke. It’s from the genre of nonsense calculation. This one starts off with what’s almost a cliche, at least for mathematics and physics majors. The equation it starts with, e^{i Pi} = -1 , is true. And famous. It should be. It links exponentiation, imaginary numbers, π, and negative numbers. Nobody would have seen it coming. And from there is the sort of typical gibberish reasoning, like writing “Pi” instead of π so that it can be thought of as “P times i”, to draw to the silly conclusion that P = 0. That much work is legitimate.

    From there it sidelines into “P = NP”, which is another equation famous to mathematicians and computer scientists. It’s a shorthand expression of a problem about how long it takes to find solutions. That is, how many steps it takes. How much time it would take a computer to solve a problem. You can see why it’s important to have some study of how long it takes to do a problem. It would be poor form to tie up your computer on a problem that won’t be finished before the computer dies of old age. Or just take too long to be practical.

    Most problems have some sense of size. You can look for a solution in a small problem or in a big one. You expect searching for the solution in a big problem to take longer. The question is how much longer? Some methods of solving problems take a length of time that grows only slowly as the size of the problem grows. Some take a length of time that grows crazy fast as the size of the problem grows. And there are different kinds of time growth. One kind is called Polynomial, because everything is polynomials. But there’s a polynomial in the problem’s size that describes how long it takes to solve. We call this kind of problem P. Another is called Non-Deterministic Polynomial, for problems that … can’t. We assume. We don’t know. But we know some problems that look like they should be NP (“NP Complete”, to be exact).

    It’s an open question whether P and NP are the same thing. It’s possible that everything we think might be NP actually can be solved by a P-class algorithm we just haven’t thought of yet. It would be a revolution in our understanding of how to find solutions if it were. Most people who study algorithms think P is not NP. But that’s mostly (as I understand it) because it seems like if P were NP then we’d have some leads on proving that by now. You see how this falls short of being rigorous. But it is part of expertise to get a feel for what seems to make sense in light of everything else we know. We may be surprised. But it would be inhuman not to have any expectations of a problem like this.

    Mark Anderson’s Andertoons for the 8th gives us the Andertoons content for the week. It’s a fair question why a right triangle might have three sides, three angles, three vertices, and just the one hypotenuse. The word’s origin, from Greek, meaning “stretching under” or “stretching between”. It’s unobjectionable that we might say this is the stretch from one leg of the right triangle to another. But that leaves unanswered why there’s just the one hypothenuse, since the other two legs also stretch from the end of one leg to another. Dr Sarah on The Math Forum suggests we need to think of circles. Draw a circle and a diameter line on it. Now pick any point on the circle other than where the diameter cuts it. Draw a line from one end of the diameter to your point. And from your point to the other end of the diameter. You have a right triangle! And the hypothenuse is the leg stretching under the other two. Yes, I’m assuming you picked a point above the diameter. You did, though, didn’t you? Humans do that sort of thing.

    I don’t know if Dr Sarah’s explanation is right. It sounds plausible and sensible. But those are weak pins to hang an etymology on. But I have no reason to think she’s mistaken. And the explanation might help people accept there is the one hypothenuse and there’s something interesting about it.

    The first (and as I write this only) commenter, Kristiaan, has a good if cheap joke there.

     
    • davekingsbury 10:38 pm on Monday, 14 November, 2016 Permalink | Reply

      I reckon it was Bob Newhart’s sketch about it that made the monkey idea so popular. Best bit, something like, hey one of them has something over here er to be or not to be that is the … gezoinebplatf!

      Like

      • Joseph Nebus 3:35 am on Sunday, 20 November, 2016 Permalink | Reply

        I like to think that helped. I fear that that particular routine’s been forgotten, though. I was surprised back in the 90s when I was getting his albums and ran across that bit, as I’d never heard it before. But it might’ve been important in feeding the idea to other funny people. There’s probably a good essay to be written tracing the monkeys at typewriters through pop culture.

        Liked by 1 person

  • Joseph Nebus 6:00 pm on Tuesday, 25 October, 2016 Permalink | Reply
    Tags: arithmetic, , , , origami   

    Reading the Comics, October 22, 2016: The Jokes You Can Make About Fractions Edition 


    Last week had a whole bundle and a half of mathematically-themed comics so let me finish off the set. Also let me refresh my appeal for words for my End Of 2016 Mathematics A To Z. There’s all sorts of letters not yet claimed; please think of a mathematical term and request it!

    David L Hoyt and Jeff Knurek’s Jumble for the 19th gives us a chance to do some word puzzle games again. If you like getting the big answer without doing the individual words then pay attention to the blackboard in the comic. Just saying.

    DUEGN O-O-O; NERDT OOO--; NINBUO OO--O-; MUURQO ---OO; The teacher was happy that those who did poorly on the math test were -----------.

    David L Hoyt and Jeff Knurek’s Jumble for the 19th of October, 2016. The link will probably expire in about a month. Have to say, it’s not a big class. I’m not surprised the students are doing well.

    Patrick J Marran’s Francis for the 20th features origami, as well as some of the more famous polyhedrons. The study of what shapes you can make from a flat sheet by origami processes — just folding, no cutting — is a neat one. Apparently origami geometry can be built out of seven axioms. I’m delighted to learn that the axioms were laid out as recently as 1992, with the exception of one that went unnoticed until 2002.

    Gabby describes her shape as an isocahedron, which must be a typo. We all make them. There’s icosahedrons which look like that figure and I’ve certainly slipped consonants around that way.

    I’m surprised and delighted to find there are ways to make an origami icosahedron. Her figure doesn’t look much like the origami icosahedron of those instructions, but there are many icosahedrons. The name just means there are 20 faces to the polyhedron so there’s a lot of room for variants.

    If you were wondering, yes, the Francis of the title is meant to be the Pope. It’s kind of a Pope Francis fan comic. I cannot explain this phenomenon.

    Rick Detorie’s One Big Happy rerun for the 21st retells one of the standard jokes you can always make about fractions. Fortunately it uses that only as part of the setup, which shows off why I’ve long liked Detorie’s work. Good cartoonists — good writers — take a stock joke and add something to make it fit their characters.

    I’ve featured Richard Thompson’s Poor Richard’s Almanac rerun from the 21st before. I’ll surely feature it again. I just like Richard Thompson art like this. This is my dubious inclusion of the essay. In “What’s New At The Zoo” he tosses off a mention of chimpanzees now typing at 120 words per minute. A comic reference to the famous thought experiment of a monkey, or a hundred monkeys, or infinitely many monkeys given typewriters and time to write all the works of literature? Maybe. Or it might just be that it’s a funny idea. It is, of course.

    'Dad, will you check my math homework?' 'Um, it looks like you wrote two different answers to every problem. Shouldn't there be just one?' 'I like to increase my odds.'

    Rick Kirkman and Jerry Scott’s Baby Blues for the 22nd of October, 2016. I’m not quite curious enough to look, but do wonder how far into the comments you have to go before someone slags on the Common Core. But then I would say if Hammy were to write down first an initial-impression guess of about what the answer should be — say, that “37 + 42” should be a number somewhere around 80 — and then an exact answer, then that would be consistent with what I understand Common Core techniques encourage and a pretty solid approach.

    In Rick Kirkman and Jerry Scott’s Baby Blues for the 22nd Hammie offers multiple answers to each mathematics problem. “I like to increase my odds,” he says. For arithmetic problems, that’s not really helping. But it is often useful, especially in modeling complicated systems, to work out multiple answers. If you’re not sure how something should behave, and it’s troublesome to run experiments, then try develop several different models. If the models all describe similar behavior, then, good! It’s reason to believe you’re probably right, or at least close to right. If the models disagree about their conclusions then you need information. You need experimental results. The ways your models disagree can inspire new experiments.

    Mark Leiknes’s Cow and Boy rerun for the 22nd is another with one of the standard jokes you can make about fractions. I suspect I’ve featured this before too, but I quite like Cow and Boy. It’s sad that the strip was cancelled, and couldn’t make a go of it as web comic. I’m not surprised; the strip had so many running jokes it might as well have had a deer and an orca shooting rocket-propelled grenades at new readers. But it’s grand seeing the many, many, many running jokes as they were first established. This is part of the sequence in which Billy, the Boy of the title, discovers there’s another kid named Billy in the class, quickly dubbed Smart Billy for reasons the strip makes clear.

     
  • Joseph Nebus 6:00 pm on Sunday, 2 October, 2016 Permalink | Reply
    Tags: , arithmetic, ,   

    Reading the Comics, October 1, 2016: Jumble Is Back Edition 


    Comic Strip Master Command sent another normal-style week for mathematics references. There’s not much that lets me get really chatty or gossippy about mathematics lore. That’s all right. The important thing is: we’ve got Jumble back.

    Greg Cravens’s The Buckets for the 25th features a bit of parental nonsense-telling. The rather annoying noise inside a car’s cabin when there’s one window open is the sort of thing fluid mechanics ought to be able to study. I see references claiming this noise to be a Helmholz Resonance. This is a kind of oscillation in the air that comes from wind blowing across the lone hole in a solid object. Wikipedia says it’s even the same phenomenon producing an ocean-roar in a seashell held up to the ear. It’s named for Hermann von Helmholtz, who described it while studying sound and vortices. Helmholz is also renowned for making a clear statement of the conservation of energy — an idea many were working towards, mind — and in thermodynamics and electromagnetism and for that matter how the eye works. Also how fast nerves transmit signals. All that said, I’m not sure that all the unpleasant sound heard and pressure felt from a single opened car window is Helmholz Resonance. Real stuff is complicated and the full story is always more complicated than that. I wouldn’t go farther than saying that Helmholz Resonance is one thing to look at.

    Michael Cavna’s Warped for the 25th uses two mathematics-cliché equations as “amazingly successful formulas”. One can quibble with whether Einstein should be counted under mathematics. Pythagoras, at least for the famous theorem named for him, nobody would argue. John Grisham, I don’t know, the joke seems dated to me but we are talking about the comics.

    Tony Carrillos’ F Minus for the 28th uses arithmetic as as something no reasonable person can claim is incorrect. I haven’t read the comments, but I am slightly curious whether someone says something snarky about Common Core mathematics — or even the New Math for crying out loud — before or after someone finds a base other than ten that makes the symbols correct.

    Cory Thomas’s college-set soap-opera strip Watch Your Head for the 28th name-drops Introduction to Functional Analysis. It won’t surprise you it’s a class nobody would take on impulse. It’s an upper-level undergraduate or a grad-student course, something only mathematics majors would find interesting. But it is very interesting. It’s the reward students have for making it through Real Analysis, the spirit-crushing course about why calculus works. Functional Analysis is about what we can do with functions. We can make them work like numbers. We can define addition and multiplication, we can measure their size, we can create sequences of them. We can treat functions almost as if they were numbers. And while we’re working on things more abstract and more exotic than the ordinary numbers Real Analysis depends on, somehow, Functional Analysis is easier than Real Analysis. It’s a wonder.

    Mark Anderson’s Andertoons for the 29th features a student getting worried about the order of arithmetic operations. I appreciate how kids get worried about the feelings of things like that. Although, truly, subtraction doesn’t go “last”; addition and subtraction have the same priority. They share the bottom of the pile, though. Multiplication and division similarly share a priority, above addition-and-subtraction. Many guides to the order of operations say to do addition-and-subtraction in order left to right, but that’s not so. Setting a left-to-right order is okay for deciding where to start. But you could do a string of additions or subtractions in any order and get the same answer, unless the expression is inconsistent.

    Four people sitting at a table divided up as a pie chart. The one sitting behind the overwhelming majority of the chunk says, 'C'mon guys ... I feel like I'm doing all the work here.'

    Daniel Beyer’s Long Story Short for the 30th of September, 2016. I think Randolph Itch, 2am did this joke too but then had everyone retire to the bar chart.

    Daniel Beyer’s Long Story Short for the 30th is a pie chart joke. There’s not a lot of mathematics to it, but I’m amused.

    Justin Boyd’s Invisible Bread for the 30th has maybe my favorite dumb joke of the week. It’s just a kite that’s proven its knowledge of mathematics. I’m a little surprised the kite didn’t call out a funnier number, by which I mean 37, but perhaps … no, that doesn’t work, actually. Of course the kite would be comfortable with higher mathematics.

    LIPOS O-O-O; PURTE OO---; VONPER -OO---; YETMSS --O-OO. Her students were beginning to understand addition and subtraction OOOO OO OOOO.

    David L Hoyt and Jeff Knurek’s Jumble for the 1st of October, 2016. I don’t know that there even is a permanent link for this that would be any good.

    And as promised, David L Hoyt and Jeff Knurek’s Jumble for the 1st of October mentions mathematics. That’s enough for me to include here.

     
  • Joseph Nebus 6:00 pm on Sunday, 18 September, 2016 Permalink | Reply
    Tags: , arithmetic, , , , ,   

    Reading the Comics, September 17, 2016: Show Your Work Edition 


    As though to reinforce how nothing was basically wrong, Comic Strip Master Command sent a normal number of mathematically themed comics around this past week. They bunched the strips up in the first half of the week, but that will happen. It was a fun set of strips in any event.

    Rob Harrell’s Adam @ Home for the 11th tells of a teacher explaining division through violent means. I’m all for visualization tools and if we are going to use them, the more dramatic the better. But I suspect Mrs Clark’s students will end up confused about what exactly they’ve learned. If a doll is torn into five parts, is that communicating that one divided by five is five? If the students were supposed to identify the mass of the parts of the torn-up dolls as the result of dividing one by five, was that made clear to them? Maybe it was. But there’s always the risk in a dramatic presentation that the audience will misunderstand the point. The showier the drama the greater the risk, it seems to me. But I did only get the demonstration secondhand; who knows how well it was done?

    Greg Cravens’ The Buckets for the 11th has the kid, Toby, struggling to turn a shirt backwards and inside-out without taking it off. As the commenters note this is the sort of problem we get into all the time in topology. The field is about what can we say about shapes when we don’t worry about distance? If all we know about a shape is the ways it’s connected, the number of holes it has, whether we can distinguish one side from another, what else can we conclude? I believe Gocomics.com commenter Mike is right: take one hand out the bottom of the shirt and slide it into the other sleeve from the outside end, and proceed from there. But I have not tried it myself. I haven’t yet started wearing long-sleeve shirts for the season.

    Bill Amend’s FoxTrot for the 11th — a new strip — does a story problem featuring pizzas cut into some improbable numbers of slices. I don’t say it’s unrealistic someone might get this homework problem. Just that the story writer should really ask whether they’ve ever seen a pizza cut into sevenths. I have a faint memory of being served a pizza cut into tenths by same daft pizza shop, which implies fifths is at least possible. Sevenths I refuse, though.

    Mark Tatulli’s Heart of the City for the 12th plays on the show-your-work directive many mathematics assignments carry. I like Heart’s showiness. But the point of showing your work is because nobody cares what (say) 224 divided by 14 is. What’s worth teaching is the ability to recognize what approaches are likely to solve what problems. What’s tested is whether someone can identify a way to solve the problem that’s likely to succeed, and whether that can be carried out successfully. This is why it’s always a good idea, if you are stumped on a problem, to write out how you think this problem should be solved. Writing out what you mean to do can clarify the steps you should take. And it can guide your instructor to whether you’re misunderstanding something fundamental, or whether you just missed something small, or whether you just had a bad day.

    Norm Feuti’s Gil for the 12th, another rerun, has another fanciful depiction of showing your work. The teacher’s got a fair complaint in the note. We moved away from tally marks as a way to denote numbers for reasons. Twelve depictions of apples are harder to read than the number 12. And they’re terrible if we need to depict numbers like one-half or one-third. Might be an interesting side lesson in that.

    Brian Basset’s Red and Rover for the 14th is a rerun and one I’ve mentioned in these parts before. I understand Red getting fired up to be an animator by the movie. It’s been a while since I watched Donald Duck in Mathmagic Land but my recollection is that while it was breathtaking and visually inventive it didn’t really get at mathematics. I mean, not at noticing interesting little oddities and working out whether they might be true always, or sometimes, or almost never. There is a lot of play in mathematics, especially in the exciting early stages where one looks for a thing to prove. But it’s also in seeing how an ingenious method lets you get just what you wanted to know. I don’t know that the short demonstrates enough of that.

    Punkinhead: 'Can you answer an arithmetic question for me, Julian?' Julian: 'Sure.' Punkinhead: 'What is it?'

    Bud Blake’s Tiger rerun for the 15th of September, 2016. I don’t get to talking about the art of the comics here, but, I quite like Julian’s expressions here. And Bud Blake drew fantastic rumpled clothes.

    Bud Blake’s Tiger rerun for the 15th gives Punkinhead the chance to ask a question. And it’s a great question. I’m not sure what I’d say arithmetic is, not if I’m going to be careful. Offhand I’d say arithmetic is a set of rules we apply to a set of things we call numbers. The rules are mostly about how we can take two numbers and a rule and replace them with a single number. And these turn out to correspond uncannily well with the sorts of things we do with counting, combining, separating, and doing some other stuff with real-world objects. That it’s so useful is why, I believe, arithmetic and geometry were the first mathematics humans learned. But much of geometry we can see. We can look at objects and see how they fit together. Arithmetic we have to infer from the way the stuff we like to count works. And that’s probably why it’s harder to do when we start school.

    What’s not good about that as an answer is that it actually applies to a lot of mathematical constructs, including those crazy exotic ones you sometimes see in science press. You know, the ones where there’s this impossibly complicated tangle with ribbons of every color and a headline about “It’s Revolutionary. It’s 46-Dimensional. It’s Breaking The Rules Of Geometry. Is It The Shape That Finally Quantizes Gravity?” or something like that. Well, describe a thing vaguely and it’ll match a lot of other things. But also when we look to new mathematical structures, we tend to look for things that resemble arithmetic. Group theory, for example, is one of the cornerstones of modern mathematical thought. It’s built around having a set of things on which we can do something that looks like addition. So it shouldn’t be a surprise that many groups have a passing resemblance to arithmetic. Mathematics may produce universal truths. But the ones we see are also ones we are readied to see by our common experience. Arithmetic is part of that common experience.

    'Dude, you have something on your face.' 'Food? Ink? Zit? What??' 'I think it's math.' 'Oh, yeah. I fell asleep on my Calculus book.'

    Jerry Scott and Jim Borgman’s Zits for the 14th of September, 2016. Properly speaking that is ink on his face, but I suppose saying it’s calculus pins down where it came from. Just observing.

    Also Jerry Scott and Jim Borgman’s Zits for the 14th I think doesn’t really belong here. It’s just got a cameo appearance by the concept of mathematics. Dave Whamond’s Reality Check for the 17th similarly just mentions the subject. But I did want to reassure any readers worried after last week that Pierce recovered fine. Also that, you know, for not having a stomach for mathematics he’s doing well carrying on. Discipline will carry one far.

     
    • ivasallay 3:44 am on Monday, 19 September, 2016 Permalink | Reply

      You said, “Twelve depictions of apples are harder to read than the number 12.” It might be a little difficult to see at first, but the twelve apples were arranged to form the numerals 1 and 2. I thought it was rather clever.

      Like

  • Joseph Nebus 6:00 pm on Sunday, 7 August, 2016 Permalink | Reply
    Tags: arithmetic, discovery, divisors, ,   

    Reading the Comics, August 1, 2016: Kalends Edition 


    The last day of July and first day of August saw enough mathematically-themed comic strips to fill a standard-issue entry. The rest of the week wasn’t so well-stocked. But I’ll cover those comics on Tuesday if all goes well. This may be a silly plan, but it is a plan, and I will stick to that.

    Johnny Hart’s Back To BC reprints the venerable and groundbreaking comic strip from its origins. On the 31st of July it reprinted a strip from February 1959 in which Peter discovers mathematics. The work’s elaborate, much more than we would use to solve the problem today. But it’s always like that. Newly-discovered mathematics is much like any new invention or innovation, a rickety set of things that just barely work. With time we learn better how the idea should be developed. And we become comfortable with the cultural assumptions going into the work. So we get more streamlined, faster, easier-to-use mathematics in time.

    The early invention of mathematics reappears the 1st of August, in a strip from earlier in February 1959. In this case it’s the sort of word problem confusion strip that any comic with a student could do. That’s a bit disappointing but Hart had much less space than he’d have for the Sunday strip above. One must do what one can.

    Mac King and Bill King’s Magic in a Minute for the 31st maybe isn’t really mathematics. I guess there’s something in the modular-arithmetic implied by it. But it depends on a neat coincidence. Follow the directions in the comic about picking a number from one to twelve and counting out the letters in the word for that number. And then the letters in the word for the number you’re pointing to, and then once again. It turns out this leads to the same number. I’d never seen this before and it’s neat that it does.

    Rick Detorie’s One Big Happy rerun for the 31st features Ruthie teaching, as she will. She mentions offhand the “friendlier numbers”. By this she undoubtedly means the numbers that are attractive in some way, like being nice to draw. There are “friendly numbers”, though, as number theorists see things. These are sets of numbers. For each number in this set you get the same index if you add together all its divisors (including 1 and the original number) and divide it by the original number. For example, the divisors of six are 1, 2, 3, and 6. Add that together and you get 12; divide that by the original 6 and you get 2. The divisors of 28 are 1, 2, 4, 7, 14, and 28. Add that pile of numbers together and you get 56; divide that by the original 28 and you get 2. So 6 and 28 are friendly numbers, each the friend of the other.

    As often happens with number theory there’s a lot of obvious things we don’t know. For example, we know that 1, 2, 3, 4, and 5 have no friends. But we do not know whether 10 has. Nor 14 nor 20. I do not know if it is proved whether there are infinitely many sets of friendly numbers. Nor do I know if it is proved whether there are infinitely many numbers without friends. Those last two sentences are about my ignorance, though, and don’t reflect what number theory people know. I’m open to hearing from people who know better.

    There are also things called “amicable numbers”, which are easier to explain and to understand than “friendly numbers”. A pair of numbers are amicable if the sum of one number’s divisors is the other number. 220 and 284 are the smallest pair of amicable numbers. Fermat found that 17,296 and 18,416 were an amicable pair; Descartes found that 9,363,584 and 9,437,056 were. Both pairs were known to Arab mathematicians already. Amicable pairs are easy enough to produce. From the tenth century we’ve had Thâbit ibn Kurrah’s rule, which lets you generate sets of numbers. Ruthie wasn’t thinking of any of this, though, and was more thinking how much fun it is to write a 7.

    Terry Border’s Bent Objects for the 1st just missed the anniversary of John Venn’s birthday and all the joke Venn Diagrams that were going around at least if your social media universe looks anything like mine.

    Jon Rosenberg’s Scenes from a Multiverse for the 1st is set in “Mathpinion City”, in the “Numerically Flexible Zones”. And I appreciate it’s a joke about the politicization of science. But science and mathematics are human activities. They are culturally dependent. And especially at the dawn of a new field of study there will be long and bitter disputes about what basic terms should mean. It’s absurd for us to think that the question of whether 1 + 1 should equal 2 or 3 could even arise.

    But we think that because we have absorbed ideas about what we mean by ‘1’, ‘2’, ‘3’, ‘plus’, and ‘equals’ that settle the question. There was, if I understand my mathematics history right — and I’m not happy with my reading on this — a period in which it was debated whether negative numbers should be considered as less than or greater than the positive numbers. Absurd? Thermodynamics allows for the existence of negative temperatures, and those represent extremely high-energy states, things that are hotter than positive temperatures. A thing may get hotter, from 1 Kelvin to 4 Kelvin to a million Kelvin to infinitely many Kelvin to -1000 Kelvin to -6 Kelvin. If there are intuition-defying things to consider about “negative six” then we should at least be open to the proposition that the universal truths of mathematics are understood by subjective processes.

     
  • Joseph Nebus 6:00 pm on Tuesday, 5 July, 2016 Permalink | Reply
    Tags: , arithmetic, , , , ,   

    Reading the Comics, July 2, 2016: Ripley’s Edition 


    As I said Sunday, there were more mathematics-mentioning comic strips than I expected last week. So do please read this little one and consider it an extra. The best stuff to talk about is from Ripley’s Believe It Or Not, which may or may not count as a comic strip. Depends how you view these things.

    Randy Glasbergen’s Glasbergen Cartoons for the 29th just uses arithmetic as the sort of problem it’s easiest to hide in bed from. We’ve all been there. And the problem doesn’t really enter into the joke at all. It’s just easy to draw.

    John Graziano’s Ripley’s Believe It Or Not on the 29th shows off a bit of real trivia: that 599 is the smallest number whose digits add up to 23. And yet it doesn’t say what the largest number is. That’s actually fair enough. There isn’t one. If you had a largest number whose digits add up to 23, you could get a bigger one by multiplying it by ten: 5990, for example. Or otherwise add a zero somewhere in the digits: 5099; or 50,909; or 50,909,000. If we ignore zeroes, though, there are finitely many different ways to write a number with digits that add up to 23. This is almost an example of a partition problem. Partitions are about how to break up a set of things into groups of one or more. But in a partition proper we don’t really care about the order: 5-9-9 is as good as 9-9-5. But we can see some minor differences between 599 and 995 as numbers. I imagine there must be a name for the sort of partition problem in which order matters, but I don’t know what it is. I’ll take nominations if someone’s heard of one.

    Graziano’s Ripley’s sneaks back in here the next day, too, with a trivia almost as baffling as the proper credit for the strip. I don’t know what Graziano is getting at with the claim that Ancient Greeks didn’t consider “one” to be a number. None of the commenters have an idea either and my exhaustive minutes of researching haven’t worked it out.

    But I wouldn’t blame the Ancient Greeks for finding something strange about 1. We find something strange about it too. Most notably, of all the counting numbers 1 falls outside the classifications of “prime” and “composite”. It fits into its own special category, “unity”. It divides into every whole number evenly; only it and zero do that, if you don’t consider zero to be a whole number. It’s the multiplicative identity, and it’s the numerator in the set of unit fractions — one-half and one-third and one-tenth and all that — the first fractions that people understand. There’s good reasons to find something exceptional about 1.

    dro-mo for the 30th somehow missed both Pi Day and Tau Day. I imagine it’s a rerun that the artist wasn’t watching too closely.

    Aaron McGruder’s The Boondocks rerun for the 2nd concludes that storyline I mentioned on Sunday about Riley not seeing the point of learning subtraction. It’s always the motivation problem.

     
  • Joseph Nebus 3:00 pm on Saturday, 25 June, 2016 Permalink | Reply
    Tags: arithmetic, branding, , , , ,   

    Reading the Comics, June 25, 2016: Busy Week Edition 


    I had meant to cut the Reading The Comics posts back to a reasonable one a week. Then came the 23rd, which had something like six hundred mathematically-themed comic strips. So I could post another impossibly long article on Sunday or split what I have. And splitting works better for my posting count, so, here we are.

    Charles Brubaker’s Ask A Cat for the 19th is a soap-bubbles strip. As ever happens with comic strips, the cat blows bubbles that can’t happen without wireframes and skillful bubble-blowing artistry. It happens that a few days ago I linked to a couple essays showing off some magnificent surfaces that the right wireframe boundary might inspire. The mathematics describing how a soap bubbles’s shape should be made aren’t hard; I’m confident I could’ve understood the equations as an undergraduate. Finding exact solutions … I’m not sure I could have done. (I’d still want someone looking over my work if I did them today.) But numerical solutions, that I’d be confident in doing. And the real thing is available when you’re ready to get your hands … dirty … with soapy water.

    Rick Stromoski’s Soup To Nutz for the 19th Shows RoyBoy on the brink of understanding symmetry. To lose at rock-paper-scissors is indeed just as hard as winning is. Suppose we replaced the names of the things thrown with letters. Suppose we replace ‘beats’ and ‘loses to’ with nonsense words. Then we could describe the game: A flobs B. B flobs C. C flobs A. A dostks C. C dostks B. B dostks A. There’s no way to tell, from this, whether A is rock or paper or scissors, or whether ‘flob’ or ‘dostk’ is a win.

    Bill Whitehead’s Free Range for the 20th is the old joke about tipping being the hardest kind of mathematics to do. Proof? There’s an enormous blackboard full of symbols and the three guys in lab coats are still having trouble with it. I have long wondered why tips are used as the model of impossibly difficult things to compute that aren’t taxes. I suppose the idea of taking “fifteen percent” (or twenty, or whatever) of something suggests a need for precision. And it’ll be fifteen percent of a number chosen without any interest in making the calculation neat. So it looks like the worst possible kind of arithmetic problem. But the secret, of course, is that you don’t have to have “the” right answer. You just have to land anywhere in an acceptable range. You can work out a fraction — a sixth, a fifth, or so — of a number that’s close to the tab and you’ll be right. So, as ever, it’s important to know how to tell whether you have a correct answer before worrying about calculating it.

    Allison Barrows’s Preeteena rerun for the 20th is your cheerleading geometry joke for this week.

    'I refuse to change my personality just for a stupid speech.' 'Fi, you wouldn't have to! In fact, make it an asset! Brand yourself as The Math Curmudgeon! ... The Grouchy Grapher ... The Sour Cosine ... The Number Grump ... The Count of Carping ... The Kvetching Quotient' 'I GET IT!'

    Bill Holbrook’s On The Fastrack for the 22nd of June, 2016. There are so many bloggers wondering if Holbrook is talking about them.

    I am sure Bill Holbrook’s On The Fastrack for the 22nd is not aimed at me. He hangs around Usenet group rec.arts.comics.strips some, as I do, and we’ve communicated a bit that way. But I can’t imagine he thinks of me much or even at all once he’s done with racs for the day. Anyway, Dethany does point out how a clear identity helps one communicate mathematics well. (Fi is to talk with elementary school girls about mathematics careers.) And bitterness is always a well-received pose. Me, I’m aware that my pop-mathematics brand identity is best described as “I guess he writes a couple things a week, doesn’t he?” and I could probably use some stronger hook, somewhere. I just don’t feel curmudgeonly most of the time.

    Darby Conley’s Get Fuzzy rerun for the 22nd is about arithmetic as a way to be obscure. We’ve all been there. I had, at first, read Bucky’s rating as “out of 178 1/3 π” and thought, well, that’s not too bad since one-third of π is pretty close to 1. But then, Conley being a normal person, probably meant “one-hundred seventy-eight and a third”, and π times that is a mess. Well, it’s somewhere around 550 or so. Octave tells me it’s more like 560.251 and so on.

     
  • Joseph Nebus 3:00 pm on Sunday, 12 June, 2016 Permalink | Reply
    Tags: arithmetic, handwriting, , perfection, , texting,   

    Reading the Comics, June 11, 2016: Mostly Mathematics As A Signifier Edition 


    For this week’s roundup of mathematically themed comic strips I have a picture again! After a month or so. It’s great to see again. Also there’s several comics I could swear I’ve shown and featured before. But it’s really quite hot here and I don’t feel like going to the effort of looking. If I repeat myself, so I do. I bet you’ve forgotten the last time I did this Robbie and Bobby too.

    Carol Lay’s Lay Lines for the 6th implicitly uses mathematics as an example of perfection. The idea of the straight line is in that territory shared by both mathematics and Platonic ideals. We can imagine a straight line and understand many properties of it even though it can’t be manifest in our real world. The Gods, allegedly, would be able to overcome that and offer perfect circles around imperfect lines. I suppose that’s one way to tell there’s a god involved. The strip also take a moment to riff on the ontological problem, although I don’t know if that’s part of Lay’s intent.

    Jonathan Lemon’s Rabbits Against Magic for the 6th uses a bit of mathematics to represent having a theory. It’s true enough that mathematics serves this role in many sciences. We can often put a good explanation for phenomena in a set of equations. But that’s so if you have a good idea what quantities to measure, and how they affect one another. Lettuce’s equation just describes how long an arc within a circle is. It’s true, although I don’t think it rates the status of a theory; it just describes one thing we’d like to know in terms of another thing. And it’s all a setup for a π joke anyway.

    Tiger: 'If I had four apples in this hand and four more in this hand, what would I have?' Punkinhead: 'Really, really big giant hands!'

    Bud Blake’s Tiger for the 8th of June, 2016. Does this joke seem at all familiar?

    Bud Blake’s Tiger for the 8th, as a King Features comic, broke my drought of having images to include with Reading the Comics posts! Celebrate! It’s also the one that made me think I was getting reruns in. But it’s more mysterious than that. The Tiger rerun (Blake died several years ago and all Tiger strips are reruns) for the 20th of April, 2015, is the same joke. I featured it in a Reading The Comics post back then. But it’s not the same strip. The art’s completely redrawn. I can’t fault Blake for having reused a setup-and-punchline. Every comic strip creator does this. Sometimes the cartoonist has improved the joke. (Berkeley Breathed did this several times over.) Sometimes the cartoonist probably just forgot it was done before. (There’s several Peanuts strips suggesting this.) I’m just delighted to catch someone at it.

    'If I had six apples in one hand and three apples in the other and, what would I have?' 'Really big hands!'

    Bud Blake’s Tiger for the 20th of April, 2015. A-ha!.

    Ryan Pagelow’s Buni for the 8th uses a blackboard full of mathematics as signifier for explaining the Big Questions of life. And features the traditional little error spotted by someone else. The scribbles are gibberish altogether, but they don’t need to be (and in truth couldn’t be) meaningful. I will defend the backwards-capital-sigma in the upper left of the first panel, though. Sigmas are some of those letters that get pretty sloppy treatment. You get swept up in inspiration and penmanship just collapses. Other Greek letters take some shabby treatment too. And there was a stretch of about three years when I would’ve sworn there was a letter ‘ksee’, a sort of topheavy squiggle. It doesn’t exist, but it’s pretty convenient when you need one more easy Greek letter to use.

    Jason Poland’s Robbie and Bobby for the 8th is the second strip that made me think there were reruns. I was right. It ran in September 2014, and I had it then.

    Zach Weinersmith’s Saturday Morning Breakfast Cereal for the 8th features the “scariest equation” in the universe. The board gives a good description of the quantities in the equation and the relationship makes superficial sense. But it does depend on an assumption I’m not sure about, but I will go with. Weinersmith’s argument supposes that a mis-sent text is equally likely to go to any of your contacts. I am not an experienced texter. But it seems to me that a mis-sent text is more likely to go to a contact you’d recently messaged, or one that’s close to the person you meant to contact. Suppose parents are among the people you text often, or whose contact information is stored where it’s easy to pick by accident. Then you likely send them more messages by accident than this expects. On the other hand, suppose you don’t text parents often or you store their information well away from your significant’s. Then the number of mis-sent messages given to them is lower. Without information about how you organize your contacts, we can’t say what’s a better estimate. So in ignorance we may suppose you mis-send texts to every one of your contacts equally often.

    Samson’s Dark Side of the Horse for the 9th is the numerals-as-objects joke for this time around.

    Dave Whamond’s Reality Check for the 9th uses word problems as the signifier for everything mathematics teachers want to know.

    Mell Lazarus’s Momma rerun for the 10th uses a word problem to try to quantify love. Marylou decries the result as “differential calculus”, although it’s really just high school algebra. “Differential calculus” is the funnier term, must admit. Differential calculus refers, generally, to the study of how much one quantity depends on another. On average you can expect something to change if one or more of the variables that describe it change. For example, if you make a rectangle a little larger, its area gets larger. What’s the ratio between how much the area changes and how much the lengths of the rectangle change? If you make an angled corridor wider, then a longer straight object can be fit through the corner. How much longer an object can you bring through the corridor if you make the width a tiny bit bigger? And this also tells us where maximums and minimums are. At a maximum or minimum, a quantity doesn’t change appreciably as the variables that describe it change a little bit. So we can find maximums and minimums by the differential calculus.

    Mark Anderson’s Andertoons finally gets in on the 11th. The numbers are looking good. I’m happy with it.

    Yeah, so, it wasn’t really all that hot.

     
  • Joseph Nebus 3:00 pm on Sunday, 29 May, 2016 Permalink | Reply
    Tags: arithmetic, , exponents, , ,   

    Reading the Comics, May 28, 2016: Visual Interest Will Never Reappear Edition 


    OK, that’s three weeks in a row in which all my mathematically-themed comic strips are from Gocomics. Maybe I should commission some generic Reading The Comics art from the cartoonists and artists I know. It could make things more exciting on a visually dull week like this.

    Mark Anderson’s Andertoons got its entry on the 25th. We draw the name “exponents” from the example of Michael Stifel, a 16th-century German theologian/mathematician. He’d described them as exponents in his influential 1544 book Arithmetica Integra. But I don’t know why he picked the name “exponent” rather than some other word.

    Nate Fakes’s Break of Day for the 25th is the anthropomorphic numerals gag for this week.

    Dave Blazek’s Loose Parts for the 25th is not quite the anthropomorphic shapes joke for this week. The word “isosceles” does trace back to Greek, of course. The first part comes from “isos”, meaning equal; you see the same root in terms like “isobar” and “isometric view”. The “sceles” part comes from “skelos”, meaning leg. Say what you will about an isosceles triangle, and you may as they’ve got poor hearing, but they do have two legs with the same length. If you want to say an equilateral triangle, which has three legs the same length, is an isosceles triangle you can do that. You’ll be right. But you will look like you’re trying a little too hard to make a point, the way you do if you point to a square and start off by calling it a rhombus.

    Donna A Lewis’s Reply All Lite for the 25th tries doing a joke about doing mathematics by hand being a sign of old age. If we’re talking about arithmetic … I could go along with that, grudgingly. Calculator applications are so reliable and so quick that it’s hard to justify doing arithmetic by hand unless it’s a very simple problem. If you have fun doing that, good.

    But if we’re doing real mathematics, the working out of a model and the implications of that, or working out calculus or group theory or graph theory or the like? There are surely some people who can do all this work in their heads and I am impressed by that. But much of real mathematics is working out implications of ideas, and that’s done so very well by hand. I haven’t found a way of typing in strings of expressions which makes it easier for me to think about the mathematics rather than the formatting. And I would believe in a note-taking program that was as sensitive and precise as pen on paper. I haven’t seen one yet, though. (I have small handwriting, and the applications I’ve tried turn all my writing into tiny, disconnected dots and scribbles.)

    Ralph Hagen’s The Barn for the 27th is superficially about Olbers’s Paradox. If there’s an infinitely large, infinitely old universe, then how can the night sky by dark? The light of all those stars should come together to make night even more brilliantly blazing than the daytime sun. This is a legitimate calculus problem. The reasoning is sound. The light of a star trillions upon trillions of light-years away may be impossibly faint. But there are so many stars that would be that far away that they would be, on average, about as bright as the sun is. Integral calculus tells us what happens when we have infinitely large numbers of impossibly tiny things added together. In the case of stars, infinitely many impossibly faint stars would come together to an infinitely bright night sky. That night is dark tells us: the universe can’t be infinitely large and infinitely old. There must be limits to how far away anything can be.

    The Barn reappears in my attention on the 28th, with a subverted word problem joke.

     
    • tkflor 10:31 pm on Monday, 30 May, 2016 Permalink | Reply

      Scientific American has a short explanation about the paradox: http://www.scientificamerican.com/article/why-is-the-night-sky-dark/
      In nutshell:
      The universe can be infinitely large, but the starry sky we currently observe isn’t infinitely old. Since it takes time for light to travel, there is a time delay before light from distant stars arrives to Earth. One should also take into account that stars have a finite life-span during which they emit light.

      Like

      • Joseph Nebus 3:35 am on Thursday, 2 June, 2016 Permalink | Reply

        That’s exactly so, yes. The darkness of the sky gives us a hint that there’s only a finite universe out there, or at least only a finite one we can observe. That’s one of the conclusions from straightforward reasoning that most startles and dazzles me.

        Like

  • Joseph Nebus 3:00 pm on Monday, 23 May, 2016 Permalink | Reply
    Tags: , , arithmetic, , , , pyramids   

    Reading the Comics, May 17, 2016: Again, No Pictures Edition 


    Last week’s Reading The Comics was a bunch of Gocomics.com strips. And I don’t feel the need to post the images for those, since they’re reasonably stable links. Today’s is also a bunch of Gocomics.com strips. I know how every how-to-bring-in-readers post ever says you should include images. Maybe I will commission someone to do some icons. It couldn’t hurt.

    Someone looking close at the title, with responsible eye protection, might notice it’s dated the 17th, a day this is not. There haven’t been many mathematically-themed comic strips since the 17th is all. And I’m thinking to try out, at least for a while, making the day on which a Reading the Comics post is issued regular. Maybe Monday. This might mean there are some long and some short posts, but being a bit more scheduled might help my writing.

    Mark Anderson’s Andertoons for the 14th is the charting joke for this essay. Also the Mark Anderson joke for this essay. I was all ready to start explaining ways that the entropy of something can decrease. The easiest way is by expending energy, which we can see as just increasing entropy somewhere else in the universe. The one requiring the most patience is simply waiting: entropy almost always increases, or at least doesn’t decrease. But “almost always” isn’t the same as “always”. But I have to pass. I suspect Anderson drew the chart going down because of the sense of entropy being a winding-down of useful stuff. Or because of down having connotations of failure, and the increase of entropy suggesting the failing of the universe. And we can also read this as a further joke: things are falling apart so badly that even entropy isn’t working like it ought. Anderson might not have meant for a joke that sophisticated, but if he wants to say he did I won’t argue it.

    Scott Adams’s Dilbert Classics for the 14th reprinted the comic of the 20th of March, 1993. I admit I do this sort of compulsive “change-simplifying” paying myself. It’s easy to do if you have committed to memory pairs of numbers separated by five: 0 and 5, 1 and 6, 2 and 7, and so on. So if I get a bill for (say) $4.18, I would look for whether I have three cents in change. If I have, have I got 23 cents? That would give me back a nickel. 43 cents would give me back a quarter in change. And a quarter is great because I can use that for pinball.

    Sometimes the person at the cash register doesn’t want a ridiculous bunch of change. I don’t blame them. It’s easy to suppose that someone who’s given you $5.03 for a $4.18 charge misunderstood what the bill was. Some folks will take this as a chance to complain mightily about how kids don’t learn even the basics of mathematics anymore and the world is doomed because the young will follow their job training and let machines that are vastly better at arithmetic than they are do arithmetic. This is probably what Adams was thinking, since, well, look at the clerk’s thought balloon in the final panel.

    But consider this: why would Dilbert have handed over $7.14? Or, specifically, how could he give $7.14 to the clerk but not have been able to give $2.14, which would make things easier on everybody? There’s no combination of bills — in United States or, so far as I’m aware, any major world currency — in which you can give seven dollars but not two dollars. He had to be handing over five dollars he was getting right back. The clerk would be right to suspect this. It looks like the start of a change scam, begun by giving a confusing amount of money.

    Had Adams written it so that the charge was $6.89, and Dilbert “helpfully” gave $12.14, then Dilbert wouldn’t be needlessly confusing things.

    Dave Whamond’s Reality Check for the 15th is that pirate-based find-x joke that feels like it should be going around Facebook, even though I don’t think it has been. I can’t say the combination of jokes quite makes logical sense, but I’m amused. It might be from the Reality Check squirrel in the corner.

    Nate Fakes’s Break of Day for the 16th is the anthropomorphized shapes joke for this essay. It’s not the only shapes joke, though.

    Doug Bratton’s Pop Culture Shock Therapy for the 16th is the Einstein joke for this essay.

    Rick Detorie’s One Big Happy rerun for the 17th is another shapes joke. Ruthie has strong ideas about what distinguishes a pyramid from a triangle. In this context I can’t say she’s wrong to assert what a pyramid is.

     
  • Joseph Nebus 3:00 pm on Monday, 16 May, 2016 Permalink | Reply
    Tags: arithmetic, , , , ,   

    Reading the Comics, May 12, 2016: No Pictures Again Edition 


    I’ve hardly stopped reading the comics. I doubt I could even if I wanted at this point. But all the comics this bunch are from GoComics, which as far as I’m aware doesn’t turn off access to comic strips after a couple of weeks. So I don’t quite feel justified including the images of the comics when you can just click links to them instead.

    It feels a bit barren, I admit. I wonder if I shouldn’t commission some pictures so I have something for visual appeal. There’s people I know who do comics online. They might be able to think of something to go alongside every “Student has snarky answer for a word problem” strip.

    Brian and Ron Boychuk’s The Chuckle Brothers for the 8th of May drops in an absolute zero joke. Absolute zero’s a neat concept. People became aware of it partly by simple extrapolation. Given that the volume of a gas drops as the temperature drops, is there a temperature at which the volume drops to zero? (It’s complicated. But that’s the thread I use to justify pointing out this strip here.) And people also expected there should be an absolute temperature scale because it seemed like we should be able to describe temperature without tying it to a particular method of measuring it. That is, it would be a temperature “absolute” in that it’s not explicitly tied to what’s convenient for Western Europeans in the 19th century to measure. That zero and that instrument-independent temperature idea get conflated, and reasonably so. Hasok Chang’s Inventing Temperature: Measurement and Scientific Progress is well-worth the read for people who want to understand absolute temperature better.

    Gene Weingarten, Dan Weingarten & David Clark’s Barney and Clyde for the 9th is another strip that seems like it might not belong here. While it’s true that accidents sometimes lead to great scientific discoveries, what has that to do with mathematics? And the first thread is that there are mathematical accidents and empirical discoveries. Many of them are computer-assisted. There is something that feels experimental about doing a simulation. Modern chaos theory, the study of deterministic yet unpredictable systems, has at its founding myth Edward Lorentz discovering that tiny changes in a crude weather simulation program mattered almost right away. (By founding myth I don’t mean that it didn’t happen. I just mean it’s become the stuff of mathematics legend.)

    But there are other ways that “accidents” can be useful. Monte Carlo methods are often used to find extreme — maximum or minimum — solutions to complicated systems. These are good if it’s hard to find a best possible answer, but it’s easy to compare whether one solution is better or worse than another. We can get close to the best possible answer by picking an answer at random, and fiddling with it at random. If we improve things, good: keep the change. You can see why this should get us pretty close to a best-possible-answer soon enough. And if we make things worse then … usually but not always do we reject the change. Sometimes we take this “accident”. And that’s because if we only take improvements we might get caught at a local extreme. An even better extreme might be available but only by going down an initially unpromising direction. So it’s worth allowing for some “mistakes”.

    Mark Anderson’s Andertoons for the 10th of Anderson is some wordplay on volume. The volume of boxes is an easy formula to remember and maybe it’s a boring one. It’s enough, though. You can work out the volume of any shape using just the volume of boxes. But you do need integral calculus to tell how to do it. So maybe it’s easier to memorize the formula for volumes of a pyramid and a sphere.

    Berkeley Breathed’s Bloom County for the 10th of May is a rerun from 1981. And it uses a legitimate bit of mathematics for Milo to insult Freida. He calls her a “log 10 times 10 to the derivative of 10,000”. The “log 10” is going to be 1. A reference to logarithm, without a base attached, means either base ten or base e. “log” by itself used to invariably mean base ten, back when logarithms were needed to do ordinary multiplication and division and exponentiation. Now that we have calculators for this mathematicians have started reclaiming “log” to mean the natural logarithm, base e, which is normally written “ln”, but that’s still an eccentric use. Anyway, the logarithm base ten of ten is 1: 10 is equal to 10 to the first power.

    10 to the derivative of 10,000 … well, that’s 10 raised to whatever number “the derivative of 10,000” is. Derivatives take us into calculus. They describe how much a quantity changes as one or more variables change. 10,000 is just a number; it doesn’t change. It’s called a “constant”, in another bit of mathematics lingo that reminds us not all mathematics lingo is hard to understand. Since it doesn’t change, its derivative is zero. As anything else changes, the constant 10,000 does not. So the derivative of 10,000 is zero. 10 to the zeroth power is 1.

    So, one times one is … one. And it’s rather neat that kids Milo’s age understand derivatives well enough to calculate that.

    Ruben Bolling’s Super-Fun-Pak Comix rerun for the 10th happens to have a bit of graph theory in it. One of Uncle Cap’n’s Puzzle Pontoons is a challenge to trace out a figure without retracting a line or lifting your pencil. You can’t, not this figure. One of the first things you learn in graph theory teaches how to tell, and why. And thanks to a Twitter request I’m figuring to describe some of that for the upcoming Theorem Thursdays project. Watch this space!

    Charles Schulz’s Peanuts Begins for the 11th, a rerun from the 6th of February, 1952, is cute enough. It’s one of those jokes about how a problem seems intractable until you’ve found the right way to describe it. I can’t fault Charlie Brown’s thinking here. Figuring out a way the problems are familiar and easy is great.

    Shaenon K Garrity and Jeffrey C Wells’s Skin Horse for the 12th is a “see, we use mathematics in the real world” joke. In this case it’s triangles and triangulation. That’s probably the part of geometry it’s easiest to demonstrate a real-world use for, and that makes me realize I don’t remember mathematics class making use of that. I remember it coming up some, particularly in what must have been science class when we built and launched model rockets. We used a measure of how high an angle the rocket reached, and knowledge of how far the observing station was from the launchpad. But that wasn’t mathematics class for some reason, which is peculiar.

     
  • Joseph Nebus 3:00 pm on Monday, 9 May, 2016 Permalink | Reply
    Tags: arithmetic, , , fast food, , , ,   

    Reading the Comics, May 6, 2016: Mistakes Edition 


    I knew my readership would drop off after I fell back from daily posting. Apparently it was worse than I imagined and nobody read my little blog here over the weekend. That’s fair enough; I had to tend other things myself. Still, for the purpose of maximizing the number of page views around here, taking two whole days off in a row was a mistake. There’s some more discussed in this Reading The Comics installment.

    Word problems are dull. At least at the primary-school level. There’s all these questions about trains going in different directions or ropes sweeping out areas or water filling troughs. So Aaron McGruder’s Boondocks rerun from the 5th of May (originally run the 22nd of February, 2001) is a cute change. It’s at least the start of a legitimate word problem, based on the ways the recording industry took advantage of artists in the dismal days of fifteen years ago. I’m sure that’s all been fixed by now. Fill in some numbers and the question might interest people.

    Glenn McCoy and Gary McCoy’s The Duplex for the 5th of May is a misunderstanding-fractions joke. I’m amused by the idea of messing up quarter-pound burgers. But it also brings to mind a summer when I worked for the Great Adventure amusement park and got assigned one day as cashier at the Great American Hamburger Stand. Thing is, I didn’t know anything about the stand besides the data point that they probably sold hamburgers. So customers would order stuff I didn’t know, and I couldn’t find how to enter it on the register, and all told it was a horrible mess. If you were stuck in that impossibly slow-moving line, I am sorry, but it was management’s fault; I told them I didn’t know what I was even selling. Also I didn’t know the drink cup sizes so I just charged you for whatever you said and if I gave you the wrong size I hope it was more soda than you needed.

    On a less personal note, I have heard the claim about why one-third-pound burgers failed in United States fast-food places. Several chains tried them out in the past decade and they didn’t last, allegedly because too many customers thought a third of a pound was less than a quarter pound and weren’t going to pay more for less beef. It’s … plausible enough, I suppose, because people have never been good with fractions. But I suspect the problem is more linguistic. A quarter-pounder has a nice rhythm to it. A half-pound burger is a nice strong order to say. A third-pound burger? The words don’t even sound right. You have to say “third-of-a-pound burger” to make it seem like English, and it’s a terribly weak phrase. The fast food places should’ve put their money into naming it something that suggested big-ness but not too-big-to-eat.

    Mark Tatulli’s Heart of the City for the 5th is about Heart’s dread of mathematics. Her expressed fear, that making one little mistake means the entire answer is wrong, is true enough. But how how much is that “enough”? If you add together someting that should be (say) 18, and you make it out to be 20 instead, that is an error. But that’s a different sort of error from adding them together and getting 56 instead.

    And errors propagate. At least they do in real problems, in which you are calculating something because you want to use it for something else. An arithmetic error on one step might grow, possibly quite large, with further steps. That’s trouble. This is known as an “unstable” numerical calculation, in much the way a tin of picric acid dropped from a great height onto a fire is an “unstable” chemical. The error might stay about as large as it started out being, though. And that’s less troublesome. A mistake might stay predictable. The calculation is “stable” In a few blessed cases an error might be minimized by further calculations. You have to arrange the calculations cleverly to make that possible, though. That’s an extremely stable calculation.

    And this is important because we always make errors. At least in any real calculation we do. When we want to turn, say, a formula like πr2 into a number we have to make a mistake. π is not 3.14, nor is it 3.141592, nor is it 3.14159265358979311599796346854418516. Does the error we make by turning π into some numerical approximation matter? It depends what we’re calculating, and how. There’s no escaping error and it might be a comfort to Heart, or any student, to know that much of mathematics is about understanding and managing error.

    The further adventures of Nadine and Nina and Science Friday: 'Does it depress you to know that with the expanding universe and all the countless billions and trillions of other planets, the best-looking men probably aren't even in our galaxy?'

    Joe Martin’s Boffo for the 6th of May, 2016. The link’s already expired, I bet. Yes, the panel did appear on a Sunday.

    Joe Martin’s Boffo for the 6th of May is in its way about the wonder of very large numbers. On some reasonable assumptions — that our experience is typical, that nothing is causing traits to be concentrated one way or another — we can realize that we probably will not see any extreme condition. In this case, it’s about the most handsome men in the universe probably not even being in our galaxy. If the universe is large enough and people common enough in it, that’s probably right. But we likely haven’t got the least handsome either. Lacking reason to suppose otherwise we can guess that we’re in the vast middle.

    David L Hoyt and Jeff Knurek’s Jumble for the 6th of May mentions mathematicians and that’s enough, isn’t it? Without spoiling the puzzle for anyone, I will say that “inocci” certainly ought to be a word meaning something. So get on that, word-makers.

    SMOPT ooo--; ORFPO -o--o; INCOCI o---oo; LAUNAN ooo---. The math teacher was being reprimanded because of his -----------.

    David L Hoyt and Jeff Knurek’s Jumble for the 6th of May, 2016. While ‘ORFPO’ mey not be anything, I believe there should be some company named ‘OrfPro’ that offers some kind of service.

    Dave Blazek’s Loose Parts for the 6th brings some good Venn Diagram humor back to my pages. Good. It’s been too long.

     
  • Joseph Nebus 3:00 pm on Wednesday, 4 May, 2016 Permalink | Reply
    Tags: , , arithmetic, , , , , ,   

    Reading the Comics, May 3, 2016: Lots Of Images Edition 


    After the heavy pace of March and April I figure to take it easy and settle to about a three-a-week schedule around here. That doesn’t mean that Comic Strip Master Command wants things to be too slow for me. And this time they gave me more comics than usual that have expiring URLs. I don’t think I’ve had this many pictures to include in a long while.

    Bill Whitehead’s Free Range for the 28th presents an equation-solving nightmare. From my experience, this would be … a great pain, yes. But it wouldn’t be a career-wrecking mess. Typically a problem that’s hard to solve is hard because you have no idea what to do. Given an expression, you’re allowed to do anything that doesn’t change its truth value. And many approaches might look promising without quite resolving to something useful. The real breakthrough is working out what approach should be used. For an astrophysics problem, there are some classes of key decisions to make. One class is what to include and what to omit in the model. Another class is what to approximate — and how — versus what to treat exactly. Another class is what sorts of substitutions and transformations turn the original expression into one that reveals what you want. Those are the hard parts, and those are unlikely to have been forgotten. Applying those may be tedious, and I don’t doubt it would be anguishing to have the finished work wiped out. But it wouldn’t set one back years either. It would just hurt.

    Christopher Grady’s Lunar Babboon for the 29th I classify as the “anthropomorphic numerals” joke for this essay. Boy, have we all been there.

    'Numbers are boring!' complains the audience. 'Not so. They contain high drama and narrative. Here's an expense account that was turned in to me last week. Can you create a *story* based on these numbers?' 'Once upon a time, a guy was fired for malfeasance ... ' 'If you skip right to the big finish, sure.'

    Bill Holbrook’s On The Fastrack for the 29th of April, 2016. Spoiler: there aren’t any numbers in the second panel.

    Bill Holbrook’s On The Fastrack for the 29th continues the storyline about Fi giving her STEM talk. She is right, as I see it, in attributing drama and narrative to numbers. This is most easily seen in the sorts of finance and accounting mathematics which the character does. And the inevitable answer to “numbers are boring” (or “mathematics is boring”) is surely to show how they are about people. Even abstract mathematics is about things (some) people find interesting, and that must be about the people too.

    'Look, Grandpa! I got 100% on my math test! Do you know what that means? It means that out of ten questions, I got at least half of them correct!' 'It must be that new, new, new math.' 'So many friendly numbers!'

    Rick Detorie’s One Big Happy for the 3rd of May, 2016. Ever notice how many shirt pockets Grandpa has? I’m not saying it’s unrealistic, just that it’s more than the average.

    Rick Detorie’s One Big Happy for the 16th is a confused-mathematics joke. Grandpa tosses off a New Math joke that’s reasonably age-appropriate too, which is always nice to see in a comic strip. I don’t know how seriously to take Ruthie’s assertion that a 100% means she only got at least half of the questions correct. It could be a cartoonist grumbling about how kids these days never learn anything, the same way ever past generation of cartoonists had complained. But Ruthie is also the sort of perpetually-confused, perpetually-confusing character who would get the implications of a 100% on a test wrong. Or would state them weirdly, since yes, a 100% does imply getting at least half the test’s questions right.

    Border Collies, as we know, are highly intelligent. 'Yup, the math confirms it --- we can't get by without people.'

    Niklas Eriksson’s Carpe Diem for the 3rd of May, 2016. I’m a little unnerved there seems to be a multiplication x at the end of the square root vinculum on the third line there.

    Niklas Eriksson’s Carpe Diem for the 3rd uses the traditional board full of mathematical symbols as signifier of intelligence. There’s some interesting mixes of symbols here. The c2, for example, isn’t wrong for mathematics. But it does evoke Einstein and physics. There’s the curious mix of the symbol π and the approximation 3.14. But then I’m not sure how we would get from any of this to a proposition like “whether we can survive without people”.

    'What comes after eleven?' 'I can't do it. I don't have enough fingers to count on!' Tiger hands him a baseball glove. 'Use this.'

    Bud Blake’s Tiger for the 3rd of May, 2016. How did Punkinhead get up to eleven?

    Bud Blake’s Tiger for the 3rd is a cute little kids-learning-to-count thing. I suppose it doesn’t really need to be here. But Punkinhead looks so cute wearing his tie dangling down onto the floor, the way kids wear their ties these days.

    Tony Murphy’s It’s All About You for the 3rd name-drops algebra. I think what the author really wanted here was arithmetic, if the goal is to figure out the right time based on four clocks. They seem to be trying to do a simple arithmetic mean of the time on the four clocks, which is fair if we make some assumptions about how clocks drift away from the correct time. Mostly those assumptions are that the clocks all started right and are equally likely to drift backwards or forwards, and do that drifting at the same rate. If some clocks are more reliable than others, then, their claimed time should get more weight than the others. And something like that must be at work here. The mean of 7:56, 8:02, 8:07, and 8:13, uncorrected, is 8:04 and thirty seconds. That’s not close enough to 8:03 “and five-eighths” unless someone’s been calculating wrong, or supposing that 8:02 is more probably right than 8:13 is.

     
  • Joseph Nebus 3:00 pm on Saturday, 30 April, 2016 Permalink | Reply
    Tags: , arithmetic, , ,   

    Reading the Comics, April 27, 2016: Closing The Month (April) Out Edition 


    I concede this isn’t a set of mathematically-themed comics that inspires deep discussions. That’s all right. It’s got three that I can give pictures for, which is important. Also it means I can wrap up April with another essay. This gives me two months in a row of posting something every day, and I’d have bet that couldn’t happen.

    Ted Shearer’s Quincy for the 1st of March, 1977, rerun the 25th of April, is not actually a “mathematics is useless in the real world” comic strip. It’s more about the uselessness of any school stuff in the face of problems like the neighborhood bully. Arithmetic just fits on the blackboard efficiently. There’s some sadness in the setting. There’s also some lovely artwork, though, and it’s worth noticing it. The lines are nice and expressive, and the greyscale wash well-placed. It’s good to look at.

    'I've got a question, Miss Reid, about this stuff we're learning in school.' 'What's that, Quincy?' Quincy points to the bully out the window. 'How's it gonna help us out in the real world?'

    Ted Shearer’s Quincy for the 1st of March, 1977, rerun the 25th of April, 2016. I just noticed ‘Miss Reid’ is probably a funny-character-name.

    dro-mo for the 26th I admit I’m not sure what exactly is going on. I suppose it’s a contest to describe the most interesting geometric shape. I believe the fourth panel is meant to be a representation of the tesseract, the four-dimensional analog of the cube. This causes me to realize I don’t remember any illustrations of a five-dimensional hypercube. Wikipedia has a couple, but they’re a bit disappointing. They look like the four-dimensional cube with some more lines. Maybe it has some more flattering angles somewhere.

    Bill Amend’s FoxTrot for the 26th (a rerun from the 3rd of May, 2005) poses a legitimate geometry problem. Amend likes to do this. It was one of the things that first attracted me to the comic strip, actually, that his mathematics or physics or computer science jokes were correct. “Determine the sum of the interior angles for an N-sided polygon” makes sense. The commenters at Gocomics.com are quick to say what the sum is. If there are N sides, the interior angles sum up to (N – 2) times 180 degrees. I believe the commenters misread the question. “Determine”, to me, implies explaining why the sum is given by that formula. That’s a more interesting question and I think still reasonable for a freshman in high school. I would do it by way of triangles.

    BEIRB -OO-O; CINEM OOO--; CCHITE O--OO-; RUSPRE O---OO. Two, Three, Five, and Seven will always be -- ----- -----.

    David L Hoyt and Jeff Knurek’s Jumble for the 27th of April, 2016. I bet the link’s already expired by the time you read this.

    David L Hoyt and Jeff Knurek’s Jumble for the 27th of April gives us another arithmetic puzzle. As often happens, you can solve the surprise-answer by looking hard at the cartoon and picking up the clues from there. And it gives us an anthropomorphic-numerals gag for this collection.

    Bill Holbrook’s On The Fastrack for the 28th of April has the misanthropic Fi explain some of the glories of numbers. As she says, they can be reliable, consistent partners. If you have learned something about ‘6’, then it not only is true, it must be true, at least if we are using ‘6’ to mean the same thing. This is the sort of thing that transcends ordinary knowledge and that’s so wonderful about mathematics.

    Fi's STEM talk: 'Numbers are reliable. They're consistent. They don't lie. They don't betray you. They don't pretend to be something they're NOT. x and y, on the other hand, are shifty little goobers.'

    Bill Holbrook’s On The Fastrack for the 28th of April, 2016. I don’t know why the ‘y’ would be in kind-of-cursive while the ‘x’ isn’t, but you do see this sort of thing a fair bit in normal mathematics.

    Fi describes ‘x’ and ‘y’ as “shifty little goobers”, which is a bit unfair. ‘x’ and ‘y’ are names we give to numbers when we don’t yet know what values they have, or when we don’t care what they have. We’ve settled on those names mostly in imitation of Réné Descartes. Trying to do without names is a mess. You can do it, but it’s rather like novels in which none of the characters has a name. The most skilled writers can carry that off. The rest of us make a horrid mess. So we give placeholder names. Before ‘x’ and ‘y’ mathematicians would use names like ‘the thing’ (well, ‘re’) or ‘the heap’. Anything that the quantity we talk about might measure. It’s done better that way.

     
  • Joseph Nebus 3:00 pm on Tuesday, 26 April, 2016 Permalink | Reply
    Tags: , arithmetic, , , , , weekdays   

    Reading the Comics, April 24, 2016: Mental Mathematics and Calendars Edition 


    Warning! I do some showing off in this installment of the Reading the Comics series. Please forgive me. I was feeling a little giddy.

    Scott Hilburn’s The Argyle Sweater I had just mentioned to a friend never seems to show up in these columns anymore. And Hilburn would so reliably do strips about anthropomorphized numerals. He returns on the 20th, after a hiatus of some length I haven’t actually checked here, with a name-drop of Einstein instead. I grinned, although a good part of what amused me was the look of the guy in the lower right of the panel. Funny pictures carry a comic strip far. Formulating the theory of relativity is a tricky request. The special theory … well, to do it properly takes some sophisticated work. But it doesn’t take much beyond the Pythagorean Theorem to realize that “how long” a thing is, or a time span is, is different for different observers. That’s the most important insight, I would say, and that is easily available. General relativity, which looks at accelerations and gravity, that’s another thing. I’d be interested in a popular treatment that explained enough mathematics people could make usable estimates but that could still make sense to a lay audience. Probably it’s not possible to do this. Too bad.

    Mark Tatulli’s Heart of the City just uses arithmetic because it’s a nice compact problem to give a student. It did strike me that 117 times 45 is something one could amaze people with by doing in one’s head, though. Here’s why. 117 times 100 would be easy. Multiplying by hundreds always is. 117 times 50 would be not almost as easy: that’s multiplying by 100 and dividing by two. 117 times 45 … well, that’s 117 times 50 minus 117 times 5. And if you know 117 times 50, then you know 117 times 5: it’s one-tenth that. And one-tenth of a thing is easy to find.

    Therefore: 117 times 100 is 11,700. Divide that by two and that’s kind of an ugly-looking number, isn’t it? But all’s not lost. Let me use another bit of falsework: 11,700 is 12,000 minus 300. Half that is 6,000 minus 150. Therefore, half of 11,700 is 5,850. So 117 times 50 is 5,850. One-tenth of that is 585. Therefore, 117 times 45 is 5,850 minus 585. And that will be … 5,275. Ta-da!

    Well, no, it isn’t. It’s 5,265. I messed up the carrying. I still think that’s doing well for multiplying ugly numbers like that without writing it down. It just won’t impress people who want the actual you know correct answer.

    Mark Anderson’s Andertoons wouldn’t let me down by vanishing for a while. The 21st is not explicitly a strip about extrapolating graphs. I’ll take it as such, though. Once again the art amuses me. I like the crash-up of charted bars. Yes, I saw the Schrödinger’s Cat thing two days later.

    Jef Mallett’s Frazz for the 23rd I drag into a mathematics blog because of the long historical links between calendars and mathematics. But Caulfield does talk about something that’s baffled everyone. There’s seven days to the week. There’s seven classically known heavenly bodies in the solar system, besides the Earth. Naming a day for each seems obvious now that we’ve committed to it. But why aren’t the bodies honored in order?

    Geocentrism seems like, at first, a plausible reason. The ancients wouldn’t order the sky Sun-Mercury-Venus-Moon-Mars-Jupiter-Saturn. But that doesn’t help. Geocentric models of the solar system (always, so far as I’m aware) put the Moon closest, then Mercury, then Venus, the Sun, Mars, Jupiter, and Saturn.

    The answer that, at least, gets repeated in histories of the calendar (for example, here, David Ewing Duncan’s The Calendar: The 5000-Year Struggle To Align The Clock And The Heavens — And What Happened To The Missing Ten Days, which was the first book I had on hand) amounts to a modular arithmetic thing. The Babylonians, if Duncan is right, named a planet-god for each hour of the day. (We treat the Moon and Sun as planets for this discussion.) The planet-gods took their hourly turn in order. If the first hour of the day is Saturn’s to rule, the next is Jupiter’s, then Mars’s, the Sun’s, Venus’s, Mercury’s, and the Moon’s. Then back to Saturn and the system keeps going like that.

    So if the first hour of the day is Saturn’s, then who has the first hour of the next day? … the Sun does. If the Sun has the first hour of the day, then who has the first hour of the day after that? … the Moon. And from here you know the pattern. At least you do if you understand that English derives most of its day names from the Norse gods, matched as best they can with those of the Roman State Religion. So, Tiw matches with Mars; Woden with Mercury; Thor with Jupiter; Freya with Venus. The apparently scrambled order of days, relative to the positions of the planets, amounts to what you get if you keep adding 24 to a number by modulo 7 arithmetic.

    That is, at least, the generally agreed-upon explanation. I am not aware of what actual researchers of Babylonian culture believe. Duncan, I must admit, takes a hit in his credibility by saying on the page after this that “recently chronobiologists have discovered that the seven-day cycle … may also have biological precedents”. I’m sorry but I just don’t believe him, or whoever he got that from.

    Kevin Fagan’s Drabble for the 24th amuses me by illustrating the common phenomenon. We have all taken out the calculator (or computer) to do some calculation that really doesn’t need it. I understand and am sympathetic. It’s so obviously useful to let the calculator work out 117 times 45 and get it right instantly. It’s easy to forget sometimes it’s faster to not bother with the calculator. We are all of us a little ridiculous.

     
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