Wronski’s Formula For Pi: Two Weird Tricks For Limits That Mathematicians Keep Using


Previously:


So now a bit more on Józef Maria Hoëne-Wronski’s attempted definition of π. I had got it rewritten to this form:

\displaystyle  \lim_{x \to \infty} f(x) = \lim_{x \to \infty} -2 x 2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)

And I’d tried the first thing mathematicians do when trying to evaluate the limit of a function at a point. That is, take the value of that point and put it in whatever the formula is. If that formula evaluates to something meaningful, then that value is the limit. That attempt gave this:

-2 \cdot \infty \cdot 1 \cdot 0

Because the limit of ‘x’, for ‘x’ at ∞, is infinitely large. The limit of ‘2^{\frac{1}{2}\cdot\frac{1}{x}} ‘ for ‘x’ at ∞ is 1. The limit of ‘\sin(\frac{\pi}{4}\cdot\frac{1}{x}) for ‘x’ at ∞ is 0. We can take limits that are 0, or limits that are some finite number, or limits that are infinitely large. But multiplying a zero times an infinity is dangerous. Could be anything.

Mathematicians have a tool. We know it as L’Hôpital’s Rule. It’s named for the French mathematician Guillaume de l’Hôpital, who discovered it in the works of his tutor, Johann Bernoulli. (They had a contract giving l’Hôpital publication rights. If Wikipedia’s right the preface of the book credited Bernoulli, although it doesn’t appear to be specifically for this. The full story is more complicated and ambiguous. The previous sentence may be said about most things.)

So here’s the first trick. Suppose you’re finding the limit of something that you can write as the quotient of one function divided by another. So, something that looks like this:

\displaystyle  \lim_{x \to a} \frac{h(x)}{g(x)}

(Normally, this gets presented as ‘f(x)’ divided by ‘g(x)’. But I’m already using ‘f(x)’ for another function and I don’t want to muddle what that means.)

Suppose it turns out that at ‘a’, both ‘h(x)’ and ‘g(x)’ are zero, or both ‘h(x)’ and ‘g(x)’ are ∞. Zero divided by zero, or ∞ divided by ∞, looks like danger. It’s not necessarily so, though. If this limit exists, then we can find it by taking the first derivatives of ‘h’ and ‘g’, and evaluating:

\displaystyle  \lim_{x \to a} \frac{h'(x)}{g'(x)}

That ‘ mark is a common shorthand for “the first derivative of this function, with respect to the only variable we have around here”.

This doesn’t look like it should help matters. Often it does, though. There’s an excellent chance that either ‘h'(x)’ or ‘g'(x)’ — or both — aren’t simultaneously zero, or ∞, at ‘a’. And once that’s so, we’ve got a meaningful limit. This doesn’t always work. Sometimes we have to use this l’Hôpital’s Rule trick a second time, or a third or so on. But it works so very often for the kinds of problems we like to do. Reaches the point that if it doesn’t work, we have to suspect we’re calculating the wrong thing.

But wait, you protest, reasonably. This is fine for problems where the limit looks like 0 divided by 0, or ∞ divided by ∞. What Wronski’s formula got me was 0 times 1 times ∞. And I won’t lie: I’m a little unsettled by having that 1 there. I feel like multiplying by 1 shouldn’t be a problem, but I have doubts.

That zero times ∞ thing, thought? That’s easy. Here’s the second trick. Let me put it this way: isn’t ‘x’ really the same thing as \frac{1}{ 1 / x } ?

I expect your answer is to slam your hand down on the table and glare at my writing with contempt. So be it. I told you it was a trick.

And it’s a perfectly good one. And it’s perfectly legitimate, too. \frac{1}{x} is a meaningful number if ‘x’ is any finite number other than zero. So is \frac{1}{ 1 / x } . Mathematicians accept a definition of limit that doesn’t really depend on the value of your expression at a point. So that \frac{1}{x} wouldn’t be meaningful for ‘x’ at zero doesn’t mean we can’t evaluate its limit for ‘x’ at zero. And just because we might not be sure that \frac{1}{x} would mean for infinitely large ‘x’ doesn’t mean we can’t evaluate its limit for ‘x’ at ∞.

I see you, person who figures you’ve caught me. The first thing I tried was putting in the value of ‘x’ at the ∞, all ready to declare that this was the limit of ‘f(x)’. I know my caveats, though. Plugging in the value you want the limit at into the function whose limit you’re evaluating is a shortcut. If you get something meaningful, then that’s the same answer you would get finding the limit properly. Which is done by looking at the neighborhood around but not at that point. So that’s why this reciprocal-of-the-reciprocal trick works.

So back to my function, which looks like this:

\displaystyle  f(x) = -2 x 2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)

Do I want to replace ‘x’ with \frac{1}{1 / x} , or do I want to replace \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right) with \frac{1}{1 / \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)} ? I was going to say something about how many times in my life I’ve been glad to take the reciprocal of the sine of an expression of x. But just writing the symbols out like that makes the case better than being witty would.

So here is a new, L’Hôpital’s Rule-friendly, version of my version of Wronski’s formula:

\displaystyle f(x) = -2 \frac{2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)}{\frac{1}{x}}

I put that -2 out in front because it’s not really important. The limit of a constant number times some function is the same as that constant number times the limit of that function. We can put that off to the side, work on other stuff, and hope that we remember to bring it back in later. I manage to remember it about four-fifths of the time.

So these are the numerator and denominator functions I was calling ‘h(x)’ and ‘g(x)’ before:

h(x) = 2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)

g(x) = \frac{1}{x}

The limit of both of these at ∞ is 0, just as we might hope. So we take the first derivatives. That for ‘g(x)’ is easy. Anyone who’s reached week three in Intro Calculus can do it. This may only be because she’s gotten bored and leafed through the formulas on the inside front cover of the textbook. But she can do it. It’s:

g'(x) = -\frac{1}{x^2}

The derivative for ‘h(x)’ is a little more involved. ‘h(x)’ we can write as the product of two expressions, that 2^{\frac{1}{2}\cdot \frac{1}{x}} and that \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right) . And each of those expressions contains within themselves another expression, that \frac{1}{x} . So this is going to require the Product Rule, of two expressions that each require the Chain Rule.

This is as far as I got with that before slamming my hand down on the table and glaring at the problem with disgust:

h'(x) = 2^{\frac{1}{2}\frac{1}{x}} \cdot \log(2) \cdot \frac{1}{2} \cdot (-1) \cdot \frac{1}{x^2} + 2^{\frac{1}{2}\frac{1}{x}} \cdot \cos( arg ) bleah

Yeah I’m not finishing that. Too much work. I’m going to reluctantly try thinking instead.

(If you want to do that work — actually, it isn’t much more past there, and if you followed that first half you’re going to be fine. And you’ll see an echo of it in what I do next time.)

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Reading the Comics, January 13, 2018: Barney Google Is Messing With My Head For Some Reason Edition


I do not know what’s possessed John Rose, cartoonist for Barney Google and Snuffy Smith — possibly the oldest syndicated comic strip not in perpetual reruns — to decide he needs to mess with my head. So far as I’m aware we haven’t ever even had any interactions. While I’ll own up to snarking about the comic strip here and there, I mean, the guy draws Barney Google and Snuffy Smith. He won’t attract the snark community of, say, Marmaduke, but he knew the job was dangerous when he took it. There’s lots of people who’ve said worse things about the comic than I ever have. He can’t be messing with them all.

There’s no mathematical content to it, but here, continuing the curious thread of Elviney and Miss Prunelly looking the same, and Elviney turning out to have a twin sister, is the revelation that Elviney’s husband also has a twin.

Loweezey: 'I know YOU have always been yore maw's fav'rit, Snuffy. Who is yore paw's?' Snuffy: 'Paw!!' Loweezey: 'Elviney, who's that wif Lukey?' Elviney: 'His brother Lucious!! They ain't seen each other fer years! But look at 'em. Thar able to pick up right whar they left off! It's like they've never been apart!' Lukey: 'Did not! Did not! Did not!' Lucius: 'Did too! Did too! Did too!'
John Rose’s Barney Google and Snuffy Smith for the 14th of January, 2018. The commenters at Comics Kingdom don’t know where this Lucius character came from so I guess now suddenly everybody in Hootin Holler is a twin and we never knew it before I started asking questions?

This means something and I don’t know what.

To mathematics:

Zach Weinersmith’s Saturday Morning Breakfast Cereal gets my attention again for the 10th. There is this famous quotation from Leopold Kronecker, one of the many 19th century German mathematicians who challenged, and set, our ideas of what mathematics is. In debates about what should count as a proof Kronecker said something translated in English to, “God created the integers, all else is the work of man”. He favored proofs that only used finite numbers, and only finitely many operations, and was skeptical of existence proofs. Those are ones that show something with desired properties must exist, without necessarily showing how to find it. Most mathematicians accept existence proofs. If you can show how to find that thing, that’s a constructive proof. Usually mathematicians like those better.

Mark Tatulli’s Heart of the City for the 11th uses a bunch of arithmetic and word problems to represent all of Dean’s homework. All looks like reasonable homework for my best guess about his age.

Jon Rosenberg’s Scenes From A Multiverse for the 11th is a fun, simple joke with some complex stuff behind it. It’s riffing on the kind of atheist who wants moral values to come from something in the STEM fields. So here’s a mathematical basis for some moral principles. There are, yes, ethical theories that have, or at least imply having, mathematics behind them. Utilitarianism at least supposes that ethical behavior can be described as measurable and computable quantities. Nobody actually does that except maybe to make video games more exciting. But it’s left with the idea that one could, and hope that this would lead to guidance that doesn’t go horribly wrong.

Don Asmussen’s Bad Reporter for the 12th uses knowledge of arithmetic as a signifier of intelligence. Common enough joke style.

Thom Bluemel’s Birdbrains for the 13th starts Pi Day observances early, or maybe supposed the joke would be too out of season were it to come in March.

Greg Evans and Karen Evans’s Luann for the 13th uses mathematics to try building up the villainy of one of the strip’s designated villains. Ann Eiffel, there, uses a heap of arithmetic to make her lingerie sale sound better. This isn’t simply a riff on people not wanting to do arithmetic, although I understand people not wanding to work out what five percent of a purchase of over $200 is. There’s a good deal of weird psychology in getting people to buy things. Merely naming a number, for example, gets people to “anchor” their expectations to it. To speak of a free gift worth $75 makes any purchase below $75 seem more economical. To speak of a chance to win $1,000 prepares people to think they’ve got a thousand dollars coming in, and that they can safely spend under that. It’s amazing stuff to learn about, and it isn’t all built on people being too lazy to figure out what five percent off of $220 would be.

T Lewis and Michael Fry’s Over the Hedge for the 13th uses &infty; along the way to making nonsense out of ice-skating judging. It’s a good way to make a hash of a rating system. Most anything done with infinitely large numbers or infinitely large sets challenges one’s intuition at least. This is part of what Leopold Kronecker was talking about.

Reading the Comics, January 9, 2018: Be Squared Edition


It wasn’t just another busy week from Comic Strip Master Command. And a week busy enough for me to split the mathematics comics into two essays. It was one where I recognized one of the panels as one I’d featured before. Multiple times. Some of the comics I feature are in perpetual reruns and don’t have your classic, deep, Peanuts-style decades of archives to draw from. I don’t usually go checking my archives to see if I’ve mentioned a comic before, not unless something about it stands out. So for me to notice I’ve seen this strip repeatedly can mean only one thing: there was something a little bit annoying about it. Recognize it yet? You will.

Hy Eisman’s Popeye for the 7th of January, 2018 is an odd place for mathematics to come in. J Wellington Wimpy regales Popeye with all the intellectual topics he tried to impress his first love with, and “Euclidean postulates in the original Greek” made the cut. And, fair enough. Euclid’s books are that rare thing that’s of important mathematics (or scientific) merit and that a lay person can just pick up and read, even for pleasure. These days we’re more likely to see a division between mathematics writing that’s accessible but unimportant (you know, like, me) or that’s important but takes years of training to understand. Doing it in the original Greek is some arrogant showing-off, though. Can’t blame Carolyn for bailing on someone pulling that stunt.

Popeye: 'Did ya ever think of gittin' hitched?' Wimpy: 'Many times! I didn't plan to be a bachelor. In fact, my first love was Carolyn. While we dined on burgers at Roughhouse's she listened to my discourse on Schopenhauer, followed by my chat that included both Kafka and Camus. Then, as I walked her home, I recited Euclidean postulates in the original Greek!' Popeye: 'Y'wuz really on a roll!' Wimpy: 'When we got to her door she said, 'Wimpy, it's been a perfect evening. Please don't spoil it by EVER asking me out again!''.
Hy Eisman’s Popeye for the 7th of January, 2018. Why does Wimpy’s shirt have a belly button?

Mark O’Hare’s Citizen Dog rerun for the 7th continues last essay’s storyline about Fergus taking Maggie’s place at school. He’s having trouble understanding the story within a story problem. I sympathize.

John Hambrock’s The Brilliant Mind of Edison Lee for the 8th is set in mathematics class. And Edison tries to use a pile of mathematically-tinged words to explain why it’s okay to read a Star Wars book instead of paying attention. Or at least to provide a response the teacher won’t answer. Maybe we can make something out of this by allowing the monetary value of something to be related to its relevance. But if we allow that then Edison’s messed up. I don’t know what quantity is measured by multiplying “every Star Wars book ever written” by “all the movies and merchandise”. But dividing that by the value of the franchise gets … some modest number in peculiar units divided by a large number of dollars. The number value is going to be small. And the dimensions are obviously crazy. Edison needs to pay better attention to the mathematics.

Teacher: 'Mister Lee, what are you reading?' Edison Lee: 'The Legends of Luke Skywalker.' Teacher: 'Ah, and how would that be relevant to this math class?' Edison: 'If you take every Star Wars book ever written, multiply them by all the movies and merchandise, and divide that by the net worth of the franchise, you have a small fortune of relevance.' (Teacher looks away.) Edison thinks: 'My mouth needs a seven-second broadcast delay.'
John Hambrock’s The Brilliant Mind of Edison Lee for the 8th of January, 2018. No, I haven’t got any idea how the third panel leads to the fourth. I mean, I know what should lead from there to there — a moment of Edison realizing he’s said something so impolitic he can’t carry on — but that moment isn’t there. The teacher seems to just shrug the whole nonsense off. Something went wrong in the composing of the joke.

Johnny Hart’s B.C. for the 14th of July, 1960 shows off the famous equation of the 20th century. All part of the comic’s anachronism-comedy chic. The strip reran the 9th of January. “E = mc2” is, correctly, associated with Albert Einstein and some of his important publications of 1905. But the expression does have some curious precursors, people who had worked out the relationship (or something close to it) before Einstein and who didn’t quite know what they had. A short piece from Scientific American a couple years back describes pre-Einstein expressions of the equation from Oliver Heaviside, Henri Poincaré, and Fritz Hasenöhrl. I’m not surprised Poincaré had something close to this; it seems like he spent twenty years almost discovering Relativity. That’s all right; he did enough in dynamical systems that mathematicians aren’t going to forget him.

Tim Lachowski’s Get A Life for the 9th is at least the fourth time I’ve seen this panel since I started doing Reading the Comics posts regularly. (Previous times: the 5th of November, 2012 and the 10th of March, 2015 and the 14th of July, 2016.) I’m like this close to concluding the strip’s in perpetual rerun and I can drop it from my daily reading.

Jason Chatfield’s Ginger Meggs for the 9th draws my eye just because the blackboard lists “Prime Numbers”. Fair enough place setting, although what’s listed are 1, 3, 5, and 7. These days mathematicians don’t tend to list 1 as a prime number; it’s inconvenient. (A lot of proofs depend on their being exactly one way to factorize a number. But you can always multiply a number by ‘1’ a couple more times without changing its value. So ‘6’ is 3 times 2, but it’s also 3 times 2 times 1, or 3 times 2 times 1 times 1, or 3 times 2 times 1145,388,434,247. You can write around that, but it’s easier to define ‘1’ as not a prime.) But it could be defended. I can’t think any reason to leave ‘2’ off a list of prime numbers, though. I think Chatfield conflated odd and prime numbers. If he’d had a bit more blackboard space we could’ve seen whether the next item was 9 or 11 and that would prove the matter.

Paul Trap’s Thatababy for the 9th uses arithmetic — square roots — as the kind of thing to test whether a computer’s working. Everyone has their little tests like this. My love’s father likes to test whether the computer knows of the band Walk The Moon or of Christine Korsgaard (a prominent philosopher in my love’s specialty). I’ve got a couple words I like to check dictionaries for. Of course the test is only any good if you know what the answer should be, and what’s the actual square root of 3,278? Goodness knows. It’s got to be between 50 (50 squared is 25 hundred) and 60 (60 squared is 36 hundred). Since 3,278 is so much closer 3,600 than 2,500 its square root should be closer to 60 than to 50. So 57-point-something is plausible. Unfortunately square roots don’t lend themselves to the same sorts of tricks from reading the last digit that cube roots do. And 3,278 isn’t a perfect square anyway. Alexa is right on this one. Also about the specific gravity of cobalt, at least if Wikipedia is right and not conspiring with the artificial intelligences on this one. Catch you in 2021.

Charles Schulz’s Peanuts for the 8th of October, 1953, is about practical uses of mathematics. It got rerun on the 9th of January.

What 2017 Looked Like To My Mathematics Blog


I do like doing a year-end recap of my readership. And WordPress seems not to be doing its annual little fireworks spectacular animated gif. This is a shame since this year, for the first time, I had two mathematics posts the same day and that would’ve been nice to see animated. (I had messed up the scheduled posting of one of the Summer 2017 A To Z, and had something else already planned to run that day, and it was either bump something too late or go ahead with two things on the same day.)

So what did readership look like for the whole year?

I published 164 posts in 2017, well down from 2016’s 213. 2016 had two A to Z sequences whereas 2017 had just the one. This was a median year for me. In 2015 I’d published 188 posts, and in 2014 a mere 129. In 2013 there were 106. (In 2012 there were 180, but that count is boosted by an experiment in also posting some space-history stuff that just didn’t fit the main content here.)

WordPress.com Traffic record for my blog in 2017. 12,214 views, 76,02 visitors, 1,094 likes, and 301 comments.
I started blogging here in late 2011. Sometime in late 2012 is when WordPress started tracking unique visitors so far as the let us know. 2018 is looking a bit flat but, you know, it’s got some promise of something or other, I like to think.

12,214 pages viewed over the 2017, which is down from 2016’s 12,851. Not very much, though, especially for how much less stuff I published. It’s a bit higher than 2015’s 11,241. I’m not sure what to make of basically flat numbers of page views over three years. Mostly I suspect, deep down, that not being able to easily read the Jumble puzzles, and occasionally include them in Reading the Comics posts, has hurt my readership and my engagement. If you know a good source for them, please, let me know.

The number of unique visitor has risen steadily, though. 2017 had the greatest number of distinct people stopping by, with 7,602 logged. In 2016 they were 7,168 in number, and in 2015 only 5,159. 2014 saw 3,382; 2013, 2,905 unique visitors. That’s a pretty dramatic growth in unique visitors per published post, a statistic that WordPress doesn’t keep and that’s of significance only because I can keep dividing things until I find some sort of trend line. Still, 2013 through 2015 it’s an almost constant 27 unique visitors per post, and then in 2016 that rose to 33 and then to 46.

The number of likes plummeted to 1,094. 2016 had seen 2,163, and 2015 — the first year I did an A to Z — some 3,273 things were liked. Comments similarly plummeted; there were 301 in 2017. 2016 saw 474, and 2015 some 822. I am not sure what I did right that first A to Z that I haven’t quite recaptured, or built upon.

For all that the 2015 through 2017 were the most-read years of my little blog here, the most popular pieces were from before that. The top five most-read posts were … well, three are ones I would have guessed. The other two surprised me:

This at least implies what to do: more polygons and game show riddles. The most popular piece from 2017 was What Would You Like In The Summer 2017 Mathematics A To Z?, my appealing for enough topics to write about for two months straight. (Blogging is never easier than when someone else gives you topics to write about.)

I got visitors from 113 nations of the world, says WordPress, and here they are:

Country Readers
United States 6973
United Kingdom 784
India 547
Canada 450
Philippines 442
Singapore 243
Australia 194
Austria 187
Germany 172
Turkey 135
Hong Kong SAR China 126
France 108
Spain 108
Brazil 107
Slovenia 104
Italy 93
Puerto Rico 78
Sweden 72
South Africa 63
Netherlands 47
Denmark 43
New Zealand 40
Switzerland 40
Thailand 37
Ireland 36
Argentina 33
Mexico 31
Israel 30
Romania 30
Russia 30
Belgium 29
Indonesia 29
Malaysia 28
Norway 26
South Korea 26
Poland 25
Japan 24
Bangladesh 21
Taiwan 20
Greece 18
Oman 17
US Virgin Islands 17
European Union 15
Finland 15
Portugal 15
Croatia 14
Pakistan 14
Ukraine 14
China 12
Colombia 12
Saudi Arabia 12
Slovakia 12
United Arab Emirates 12
Chile 11
Czech Republic 10
Nigeria 10
Uruguay 10
Bulgaria 9
Hungary 9
Vietnam 9
Kuwait 8
Egypt 7
Estonia 7
Belarus 6
Lebanon 6
Iceland 5
Jamaica 5
Nepal 5
Paraguay 5
Peru 5
Serbia 5
Venezuela 5
Cambodia 4
Costa Rica 4
Iraq 4
Saint Kitts & Nevis 4
Albania 3
Algeria 3
Armenia 3
Bosnia & Herzegovina 3
Cyprus 3
Kenya 3
Lithuania 3
Macedonia 3
Azerbaijan 2
Bahrain 2
Barbados 2
Ecuador 2
Georgia 2
Ghana 2
Jordan 2
Kazakhstan 2
Latvia 2
Luxembourg 2
Morocco 2
Northern Mariana Islands 2
Qatar 2
Sri Lanka 2
Trinidad & Tobago 2
Angola 1
Bahamas 1
Bermuda 1
Bhutan 1
Cape Verde 1
Ethiopia 1
Guam 1
Madagascar 1
Maldives 1
Malta 1
Palestinian Territories 1
Tunisia 1
Uganda 1
Zimbabwe 1

I understand being more read in countries where English is the primary language. Still seems like I had fewer readers from China than should’ve expected. I remember ages ago someone else (Elke Stangl?) mentioning a curious absence of readers from China and I’m curious whether others have observed this and, if so, what might be going on.

On the insights page WordPress tells me I had a total of 441 comments and 1,043 likes, which does not match what the traffic page was telling me. I wonder if the discrepancy in comments is about whether to count links from one posting to another, which are regarded as comments on the linked page. No idea how to explain the discrepancy in likes, though.

Insights says I got an average of three comments per post in 2017, and an average of six likes per post. At 153,483 words, in total, published that’s 936 words per post, on average. I’m curious what the statistics for earlier years were. I feel like I’m getting more longwinded, at least. (Also with 201,692 words on my humor blog this gives me a bit more than a third of a million words published last year. Not a bad heap of words.)

I am considering getting a proper, individual domain for my blog here. I confess I’ve never quite understood how being off on my own name would encourage more visitors than having a subdomain nestled under the wordpress.com label, but it seems to work for folks like Iva Sallay’s findthefactors.com. (Sallay also has two great hooks, between the puzzles and the lists of factors of whole numbers.) Maybe I just need to poke around it some more until the whole matter becomes irrelevant, and then I can act, wrongly.

Reading the Comics, January 6, 2018: Terms Edition


The last couple days of last week saw a rush of comics, although most of them were simpler things to describe. Bits of play on words, if you like.

Samson’s Dark Side of the Horse for the 4th of January, 2018, is one that plays on various meanings of “average”. The mean, alluded to in the first panel, is the average most people think of first. Where you have a bunch of values representing instances of something, add up the values, and divide by the number of instances. (Properly that’s the arithmetic mean. There’s some others, such as the geometric mean, but if someone’s going to use one of those they give you clear warning.) The median, in the second, is the midpoint, the number that half of all instances are less than. So you see the joke. If the distribution of intelligence is normal — which is a technical term, although it does mean “not freakish” — then the median and the mean should be equal. If you had infinitely many instances, and they were normally distributed, the two would be equal. With finitely many instances, the mean and the median won’t be exactly in line, for the same reason if you fairly toss a coin two million times it won’t turn up heads exactly one million times.

Dark Side of the Horse for the 5th delivers the Roman numerals joke of the year. And I did have to think about whether ‘D’ is a legitimate Roman numeral. This would be easier to remember before 1900.

Mike Lester’s Mike du Jour for the 4th is geometry wordplay. I’m not sure the joke stands up to scrutiny, but it lands well enough initially.

Johnny Hart’s Back to BC for the 5th goes to the desire to quantify and count things. And to double-check what other people tell you about this counting. It’s easy, today, to think of the desire to quantify things as natural to humans. I’m not confident that it is. The history of statistics shows this gradual increase in the number and variety of things getting tracked. This strip originally ran the 11th of July, 1960.

Bill Watterson’s Calvin and Hobbes for the 5th talks about averages again. And what a population average means for individuals. It doesn’t mean much. The glory of statistics is that groups are predictable in a way that individuals are not.

John Graziano’s Ripley’s Believe It Or Not for the 5th features a little arithmetic coincidence, that multiplying 21,978 by four reverses its digits. It made me think of Ray Kassinger’s question the other day about parasitic numbers. But this isn’t a parasitic number. A parasitic number is one with a value, multiplied by a particular number, that’s the same as you get by moving its last digit to the front. Flipping the order of digits seems like it should be something and I don’t know what.

Mark Anderson’s Andertoons for the 6th is a confident reassurance that 2018 is a normal, healthy year after all. Or can be. Prime numbers.

Mark O’Hare’s Citizen Dog rerun for the 6th is part of a sequence in which Fergus takes a (human) child’s place in school. Mathematics gets used as a subject that’s just a big pile of unfamiliar terms if you just jump right in. Most subjects are like this if you take them seriously, of course. But mathematics has got an economy of technical terms to stuff into people’s heads, and that have to be understood to make any progress. In grad school my functional analysis professor took great mercy on us, and started each class with re-writing the definitions of all the technical terms introduced the previous class. Also of terms that might be a bit older, but that are important to get right, which is why I got through it confident I knew what a Sobolev Space was. (It’s a collection of functions that have enough derivatives to do your differential equations problem.) Numerator and denominator, we’re experts on by now.

Reading the Comics, January 3, 2018: Explaining Things Edition


There were a good number of mathematically-themed comic strips in the syndicated comics last week. Those from the first part of the week gave me topics I could really sink my rhetorical teeth into, too. So I’m going to lop those off into the first essay for last week and circle around to the other comics later on.

Jef Mallett’s Frazz started a week of calendar talk on the 31st of December. I’ve usually counted that as mathematical enough to mention here. The 1st of January as we know it derives, as best I can figure, from the 1st of January as Julius Caesar established for 45 BCE. This was the first Roman calendar to run basically automatically. Its length was quite close to the solar year’s length. It had leap days added according to a rule that should have been easy enough to understand (one day every fourth year). Before then the Roman calendar year was far enough off the solar year that they had to be kept in synch by interventions. Mostly, by that time, adding a short extra month to put things more nearly right. This had gotten all confusingly messed up and Caesar took the chance to set things right, running 46 BCE to 445 days long.

But why 445 and not, say, 443 or 457? And I find on research that my recollection might not be right. That is, I recall that the plan was to set the 1st of January, Reformed, to the first new moon after the winter solstice. A choice that makes sense only for that one year, but, where to set the 1st is literally arbitrary. While that apparently passes astronomical muster (the new moon as seen from Rome then would be just after midnight the 2nd of January, but hitting the night of 1/2 January is good enough), there’s apparently dispute about whether that was the objective. It might have been to set the winter solstice to the 25th of December. Or it might have been that the extra days matched neatly the length of two intercalated months that by rights should have gone into earlier years. It’s a good reminder of the difficulty of reading motivation.

Brian Fies’s The Last Mechanical Monster for the 1st of January, 2018, continues his story about the mad scientist from the Fleischer studios’ first Superman cartoon, back in 1941. In this panel he’s describing how he realized, over the course of his long prison sentence, that his intelligence was fading with age. He uses the ability to do arithmetic in his head as proof of that. These types never try naming, like, rulers of the Byzantine Empire. Anyway, to calculate the cube root of 50,653 in his head? As he used to be able to do? … guh. It’s not the sort of mental arithmetic that I find fun.

But I could think of a couple ways to do it. The one I’d use is based on a technique called Newton-Raphson iteration that can often be used to find where a function’s value is zero. Raphson here is Joseph Raphson, a late 17th century English mathematician known for the Newton-Raphson method. Newton is that falling-apples fellow. It’s an iterative scheme because you start with a guess about what the answer would be, and do calculations to make the answer better. I don’t say this is the best method, but it’s the one that demands me remember the least stuff to re-generate the algorithm. And it’ll work for any positive number ‘A’ and any root, to the ‘n’-th power.

So you want the n-th root of ‘A’. Start with your current guess about what this root is. (If you have no idea, try ‘1’ or ‘A’.) Call that guess ‘x’. Then work out this number:

\frac{1}{n}\left( (n - 1) \cdot x + \frac{A}{x^{n - 1}} \right)

Ta-da! You have, probably, now a better guess of the n-th root of ‘A’. If you want a better guess yet, take the result you just got and call that ‘x’, and go back calculating that again. Stop when you feel like your answer is good enough. This is going to be tedious but, hey, if you’re serving a prison term of the length of US copyright you’ve got time. (It’s possible with this sort of iterator to get a worse approximation, although I don’t think that happens with n-th root process. Most of the time, a couple more iterations will get you back on track.)

But that’s work. Can we think instead? Now, most n-th roots of whole numbers aren’t going to be whole numbers. Most integers aren’t perfect powers of some other integer. If you think 50,653 is a perfect cube of something, though, you can say some things about it. For one, it’s going to have to be a two-digit number. 103 is 1,000; 1003 is 1,000,000. The second digit has to be a 7. 73 is 343. The cube of any number ending in 7 has to end in 3. There’s not another number from 1 to 9 with a cube that ends in 3. That’s one of those things you learn from playing with arithmetic. (A number ending in 1 cubes to something ending in 1. A number ending in 2 cubes to something ending in 8. And so on.)

So the cube root has to be one of 17, 27, 37, 47, 57, 67, 77, 87, or 97. Again, if 50,653 is a perfect cube. And we can do better than saying it’s merely one of those nine possibilities. 40 times 40 times 40 is 64,000. This means, first, that 47 and up are definitely too large. But it also means that 40 is just a little more than the cube root of 50,653. So, if 50,653 is a perfect cube, then it’s most likely going to be the cube of 37.

Bill Watterson’s Calvin and Hobbes rerun for the 2nd is a great sequence of Hobbes explaining arithmetic to Calvin. There is nothing which could be added to Hobbes’s explanation of 3 + 8 which would make it better. I will modify Hobbes’s explanation of what the numerator. It’s ridiculous to think it’s Latin for “number eighter”. The reality is possibly more ridiculous, as it means “a numberer”. Apparently it derives from “numeratus”, meaning, “to number”. The “denominator” comes from “de nomen”, as in “name”. So, you know, “the thing that’s named”. Which does show the terms mean something. A poet could turn “numerator over denominator” into “the number of parts of the thing we name”, or something near enough that.

Hobbes continues the next day, introducing Calvin to imaginary numbers. The term “imaginary numbers” tells us their history: they looked, when first noticed in formulas for finding roots of third- and fourth-degree polynomials, like obvious nonsense. But if you carry on, following the rules as best you can, that nonsense would often shake out and you’d get back to normal numbers again. And as generations of mathematicians grew up realizing these acted like numbers we started to ask: well, how is an imaginary number any less real than, oh, the square root of six?

Hobbes’s particular examples of imaginary numbers — “eleventenn” and “thirty-twelve” — are great-sounding compositions. They put me in mind, as many of Watterson’s best words do, of a 1960s Peanuts in which Charlie Brown is trying to help Sally practice arithmetic. (I can’t find it online, as that meme with edited text about Sally Brown and the sixty grapefruits confounds my web searches.) She offers suggestions like “eleventy-Q” and asks if she’s close, which Charlie Brown admits is hard to say.

Cherry Trail: 'Good morning, honey! Where's Dad?' Mark Trail: 'He's out on the porch reading the paper!' Cherry: 'Rusty sure is excited about our upcoming trip to Mexico!' Mark: 'Did you get everything worked out with the school?' Cherry: 'Rusty will need to do some math assignments, but he'll get credit for his other subjects since it's an educational trip!'
James Allen’s Mark Trail for the 3rd of January, 2018. James Allen has changed many things about the comic strip since Jack Elrod’s retirement, as I have observed over on the other blog. There are less ruthlessly linear stories. There’s no more odd word balloon placement implying that giant squirrels are talking about the poachers. Mark Trail sometimes has internal thoughts. I’m glad that he does still choose to over-emphasize declarations like “[Your Dad]’s out on the porch reading the paper!” There are some traditions.

And finally, James Allen’s Mark Trail for the 3rd just mentions mathematics as the subject that Rusty Trail is going to have to do some work on instead of allowing the experience of a family trip to Mexico to count. This is of extremely marginal relevance, but it lets me include a picture of a comic strip, and I always like getting to do that.

How December 2017 Treated My Mathematics Journal


Before I even look at the statistics I can say: December 2017 treated my mathematics journal better than it treated me. A third of the way in, our pet rabbit died, suddenly and unexpectedly. And this was days short of a year from our previous pet rabbit’s death. So that’s the cryptic plan-scrambling stuff I had been talking about, and why my writing productivity dropped. We don’t know when we’ll take in a new rabbit (or rabbits). Possibly this month, although not until late in January at soonest.

And … well, thank you for the condolences that I honestly do not mean to troll for. I can’t say we’re used to the idea that we lost our rabbit so soon. It’s becoming a familiar thought is all.

Our pet rabbit on the beach, nibbling a flower and peering into the camera with one big, round eye.
Don’t let the endearing cast of his eye fool you. Given the chance, he’d steal your heart.

But to the blog contents. How did they, quantifiably, go?

I fell back below a thousand page views. Just under 900, too: 899 page views over the month, from 599 unique visitors, as if both numbers were trying to tease Price Is Right Item-Up-For-Bids offerings. That’s down from the 1,052 page views in November, but only technically down from the 604 unique visitors then. October had 1,069 page views from a basically-equal 614 unique visitors. And it turns out that while I thought I stopped writing stuff, especially after our rabbit’s death, I had 11 posts in the month. That’s low but in the normal range for a month that has no A-to-Z sequence going. Curious.

There were 71 pages liked around here in December. That’s technically up from November’s 70, but not really. It’s less technically up from October’s 64. Still makes me wonder what might have happened if I’d scraped together a 12th post for the month. And the other big measure of reader involvement? 24 comments posted in December, down from November’s 28 but above October’s 12. I may need to start offering bounties for interesting comments. Or, less ridiculously, start some open threads for people who want to recommend good blogs or books or Twitter threads they’ve found.

2018 starts with a total 56,318 page views from 26,491 tracked unique visitors. The numbers don’t look bad, although I keep running across those WordPress blogs that’s, like, someone who started posting an inspirational message once a week two months ago and has just broken a million page views and gets 242 likes on every post and wonder if it’s just me. It’s not.

How about the roster of nations? For that I figure there were 53 countries sending me readers in December, technically down from November’s 56 and technically up from October’s 51. There were 15 single-reader countries, down from November’s 22 but slightly above October’s 13. And who were they? These places:

Country Readers
United States 553
Canada 47
United Kingdom 41
India 35
Ireland 19
Philippines 16
Austria 13
Germany 12
Turkey 12
Australia 11
Sweden 9
Singapore 8
France 7
Italy 7
Slovenia 7
New Zealand 6
Spain 6
Indonesia 5
Norway 5
South Korea 5
Brazil 4
Hong Kong SAR China 4
Malaysia 4
Poland 4
Belgium 3
Denmark 3
Finland 3
Japan 3
Netherlands 3
Portugal 3
Taiwan 3
Thailand 3
Argentina 2
Colombia 2
Ecuador 2
Serbia 2
Slovakia 2
United Arab Emirates 2
Albania 1
Bangladesh 1
Croatia 1
Egypt 1
Israel 1
Jamaica 1
Lebanon 1 (*)
Mexico 1 (*)
Peru 1 (*)
Romania 1 (*)
Russia 1
South Africa 1
Switzerland 1
Uruguay 1
Venezuela 1

Lebanon, Mexico, Peru, and Romania were also single-reader countries on November, and there’s no nation that’s on a three-month single-reader streak.

So what was the roster of popular posts for the month? My perennials, plus Reading the Comics, and some of that Wronski π stuff just squeaks in, tied for fifth place. What people wanted to read here was:

Have I got plans for January 2018? Yes, I have. Besides keeping on Reading the Comics, I hope to get through Wronski’s formula for π. I know there’s readers eager to find out what the punch line is. I know at least one has already worked it out and been surprised. And I’m hoping to work out a question about pinball tournaments that my love set me on. I’ve done a little thinking about the issue, and don’t believe the results, so I’m hoping to think some more and then make my computer do a bunch of simulations. Could be fun.

And I’ll be spending it hoping that you, the reader, are around. If you’re here now there’s a good chance you’re reading this. If you’d like to follow on your WordPress reader, there’s a ‘Follow on WordPress’ button in the upper right corner of the page. If you’d rather get it by e-mail, before I’ve made corrections to things that are only obviously wrong two minutes after publication, there’s the ‘Follow by e-mail’ button near that. And if you’d like to follow me on Twitter, try @Nebusj. I’m currently running only like four weeks behind on responding to follow-up tweets or direct messages, which is practically living a year in the future compared to my e-mail. Thanks for being here.

Revealed: Barney Google Lead Time, Desire To Mess With My Head


OK. Asked by me the 17th of September, 2017:

Are … are [ the Smiths’ next-door neighbor Elviney and Jughaid’s teacher Miss Prunelly ] the same character, just wearing different glasses? I’ve been reading this comic strip for like forty years and I’ve never noticed this before.

Really. Apart from their accessories the characters are the same.

And then, published by John Rose today, the 3rd of January, 2018:

Elviney, to Loweezy Smith: 'Thar's so much gossip goin' 'roun', I can hardly keep up wif it all!! But yo're in luck, Lo --- my twin sister's been able to catch whatever I miss!!' And there's a second Elviney there.
John Rose’s Barney Google and Snuffy Smith for the 3rd of January, 2017. I mean, there’s no reason Miss Prunelly can’t have a small as well as a large pair of eyeglasses, right? And if she took the pencil out of her hair she could put back in one of those … miniature Stonehenge trilithons … couldn’t she? Anyway I need help having a reaction to all this.

So. Per the US Navy’s Julian Date converter today is 2458121.5. The 17th of September was Julian Date 2458013.5. (Never try to work out the difference between two dates by yourself. Use a Julian Date converter.) So that’s 108 days, or just over 15 weeks. Good to know.

Reading the Comics, December 30, 2017: Looking To 2018 Edition


The last full week of 2017 was also a slow one for mathematically-themed comic strips. You can tell by how many bits of marginally relevant stuff I include. In this case, it also includes a couple that just mention the current or the upcoming year. So you’ve been warned.

Mac King and Bill King’s Magic in a Minute activity for the 24th is a logic puzzle. I’m not sure there’s deep mathematics to it, but it’s some fun to reason out.

John Graziano’s Ripley’s Believe It Or Not for the 24th mentions the bit of recreational group theory that normal people know, the Rubik’s Cube. The group theory comes in from rotations: you can take rows or columns on the cube and turn them, a quarter or a half or a three-quarters turn. Which rows you turn, and which ways you turn them, form a group. So it’s a toy that inspires deep questions. Who wouldn’t like to know in how few moves a cube could be solved? We know there are at least some puzzles that take 18 moves to solve. (You can calculate the number of different cube arrangements there are, and how many arrangements you could make by shuffling a cube around with 17 moves. There’s more possible arrangements than there are ones you can get to in 17 moves; therefore, there must be at least one arrangement that takes 18 moves to solve.) A 2010 computer-assisted proof by Tomas Rokicki, Herbert Kociemba, Morley Davidson, and John Dethridge showed that at most 20 face turns are needed for every possible cube to be solved. I don’t know if there’s been any success figuring out whether 19 or even 18 is necessarily enough.

Griffith: 'Here we are, Zippy, back in the land of our childhood.' Zippy: 'Are we still in the ninth grade?' Griffith: 'Kind of ... although I still can't remember a thing about algebra.' Zippy: 'So many spitballs and paper airplanes ago!!' Griffith: 'Why did I act up so much in school, Zippy? Was it a Freudian thing?' Zippy: 'It was a cry for kelp.' Griffith: 'Don't you mean a cry for help? I don't think kelp was even a word I knew back in the 50s.' Zippy: 'Seaweed is the fifth dimension!'
Bill Griffith’s Zippy the Pinhead for the 26th of December, 2017. This is not as strongly a memoir or autobiographical strip as Griffith will sometimes do, which is a shame. Those are always captivating. I have fun reading Zippy the Pinhead and understand why people wouldn’t. But the memoir strips I recommend even to people who don’t care for the usual fare.

Bill Griffith’s Zippy the Pinhead for the 26th just mentions algebra as a thing that Griffith can’t really remember, even in one of his frequent nostalgic fugues. I don’t know that Zippy’s line about the fifth dimension is meant to refer to geometry. It might refer to the band, but that would be a bit odd. Yes, I know, Zippy the Pinhead always speaks oddly, but in these nostalgic fugue strips he usually provides some narrative counterpoint.

Larry Wright’s Motley Classics for the 26th originally ran in 1986. I mention this because it makes the odd dialogue of getting “a new math program” a touch less odd. I confess I’m not sure what the kid even got. An educational game? Something for numerical computing? The coal-fired, gear-driven version of Mathematica that existed in the 1980s? It’s a mystery, it is.

Ryan Pagelow’s Buni for the 27th is really a calendar joke. It seems to qualify as an anthropomorphic numerals joke, though. It’s not a rare sentiment either.

Jef Mallett’s Frazz for the 29th is similarly a calendar joke. It does play on 2017 being a prime number, a fact that doesn’t really mean much besides reassuring us that it’s not a leap year. I’m not sure just what’s meant by saying it won’t repeat for another 2017 years, at least that wouldn’t be just as true for (say) 2015 or 2019. But as Frazz points out, we do cling to anything that floats in times like these.

Wronski’s Formula For Pi: A First Limit


Previously:

When I last looked at Józef Maria Hoëne-Wronski’s attempted definition of π I had gotten it to this. Take the function:

f(x) = -2 x 2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)

And find its limit when ‘x’ is ∞. Formally, you want to do this by proving there’s some number, let’s say ‘L’. And ‘L’ has the property that you can pick any margin-of-error number ε that’s bigger than zero. And whatever that ε is, there’s some number ‘N’ so that whenever ‘x’ is bigger than ‘N’, ‘f(x)’ is larger than ‘L – ε’ and also smaller than ‘L + ε’. This can be a lot of mucking about with expressions to prove.

Fortunately we have shortcuts. There’s work we can do that gets us ‘L’, and we can rely on other proofs that show that this must be the limit of ‘f(x)’ at some value ‘a’. I use ‘a’ because that doesn’t commit me to talking about ∞ or any other particular value. The first approach is to just evaluate ‘f(a)’. If you get something meaningful, great! We’re done. That’s the limit of ‘f(x)’ at ‘a’. This approach is called “substitution” — you’re substituting ‘a’ for ‘x’ in the expression of ‘f(x)’ — and it’s great. Except that if your problem’s interesting then substitution won’t work. Still, maybe Wronski’s formula turns out to be lucky. Fit in ∞ where ‘x’ appears and we get:

f(\infty) = -2 \infty 2^{\frac{1}{2}\cdot \frac{1}{\infty}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{\infty}\right)

So … all right. Not quite there yet. But we can get there. For example, \frac{1}{\infty} has to be — well. It’s what you would expect if you were a kid and not worried about rigor: 0. We can make it rigorous if you like. (It goes like this: Pick any ε larger than 0. Then whenever ‘x’ is larger than \frac{1}{\epsilon} then \frac{1}{x} is less than ε. So the limit of \frac{1}{x} at ∞ has to be 0.) So let’s run with this: replace all those \frac{1}{\infty} expressions with 0. Then we’ve got:

f(\infty) = -2 \infty 2^{0} \sin\left(0\right)

The sine of 0 is 0. 20 is 1. So substitution tells us limit is -2 times ∞ times 1 times 0. That there’s an ∞ in there isn’t a problem. A limit can be infinitely large. Think of the limit of ‘x2‘ at ∞. An infinitely large thing times an infinitely large thing is fine. The limit of ‘x ex‘ at ∞ is infinitely large. A zero times a zero is fine; that’s zero again. But having an ∞ times a 0? That’s trouble. ∞ times something should be huge; anything times zero should be 0; which term wins?

So we have to fall back on alternate plans. Fortunately there’s a tool we have for limits when we’d otherwise have to face an infinitely large thing times a zero.

I hope to write about this next time. I apologize for not getting through it today but time wouldn’t let me.

Reading the Comics, December 23, 2017: Slow Week Edition


Comic Strip Master Command apparently wants everybody to have a quiet time ahead of Christmas. How quiet? Quiet enough that I’m including a strip I skipped last week and probably shouldn’t have. Here goes.

Ruben Bolling’s Super-Fun-Pak Comix for the 15th was an installment of Uncle Cap’n’s Puzzle Pontoon, an activity puzzle that’s always about Uncle Cap’n running some low-competence scam. In this case the scam is bitcoins, which makes me wonder how old this particular panel rerun is. (I thought I saw a bitcoin joke in Barney Google, mind, although I can’t find the reference to prove it.)

I don’t feel confident that I understand the full mathematics behind the scheme, so I’ll pass on that. I can talk about the SHA-256 Hash Function and what it’s for, though. To be part of the bitcoin process your computer needs to do two things: it has to do some computing work, and it has to convince other computers that it’s done that. The trick is to prove it was done without giving the original work away. The answer is one that humans have known for centuries. Probably millennia. Possibly since the invention of secrets. To show you’re in on a secret, publicize something that makes no sense except to other people who know the secret. A hash is one way to do it.

It’s a function which matches a string of numbers that represent your original message to the real numbers. It should be easy to make the hash from the original string. But it should be hard to go from the hash back to the original string. So then you can publicize the hash of whatever your secret is. And someone else can know that they have the same secret by checking whether it hashes to the same number. (I’m reminded of how Galileo secured his priority of the discovery that Venus shows phases by writing a short sentence describing the phenomenon, and then publicizing an anagram of it. The anagram made no sense, but if you knew his original message you verify that yes, indeed, he did publicize that string of letters. I suppose that’s not properly a hash, but it serves much the same role.) It’s an easy enough way to add some authentication to a message, and to make it more tamper-proof. Hash functions for this kind of security are believed to be reasonably collision-proof. It might be possible to find two original messages with the same hash. But we believe it would take so long to do that it would be more effective to just break into your target’s house and steal their computer instead of counterfeiting the message.

'So, I finally used my Algebra 2 ... helping my kid with his Algebra 2.'
Hilary Price (w/KG)’s Rhymes with Orange for the 17th of December, 2017. I’m not sure who KG is. Daily strips lately have been co-signed by Rina Piccolo, formerly of Tina’s Groove.

Hilary Price’s Rhymes with Orange for the 17th is a joke about the uselessness of Algebra 2. It’s a joke of a kind with jokes about philosophy professors having jobs training students to be philosophy professors (a joke mathematicians get too, come to think of it). I’m a bit more sympathetic to joking about Algebra 2, rather than Algebra at all. There are some classes with a purpose that doesn’t seem quite clear. I’m more likely to name pre-algebra as a course whose purpose I can’t quite pin down. Algebra 2 I would, generically, expect to cover stuff like functions of several variables that you’re prepared for the first time you take Algebra, and you should be comfortable with before you start Calculus (or Pre-Calculus), but that aren’t essential to knowing algebra in the first place.

Sam Hurt’s Eyebeam for the 18th is the anthropomorphic numerals segment for this slow week and makes literal an ancient joke. Incidentally, has anyone else been seeing the follow-up joke on their social media feeds? I don’t remember seeing it before about two months ago. (The follow up is, why was it that seven ate nine? … Because one should eat three-square meals a day.)

Brant Parker and Johnny Hart’s Wizard of Id Classics for the 21st mentions mathematicians, engineers, and wizards as the epitome of intelligence and ability. Flattering thought. My love’s father just yesterday proclaimed his confidence that as a mathematics PhD I could surely figure out how to do something mechanical. Related note: in three decades of being in an adult-like state I have never once successfully changed my car’s tire without outside aid. The strip originally ran the 25th of December, 1967.

There’s no Andertoons this week. I told you it was slow.

The Arthur Christmas Season


I don’t know how you spend your December, but part of it really ought to be done watching the Aardman Animation film Arthur Christmas. It inspired me to ponder a mathematical-physics question that got into some heady territory and this is a good time to point people back to that.

The first piece is Could `Arthur Christmas’ Happen In Real Life? At one point in the movie Arthur and Grand-Santa are stranded on a Caribbean island while the reindeer and sleigh, without them, go flying off in a straight line. This raises the question of what is a straight line if you’re on the surface of something spherical like the Earth. Also, Grand-Santa is such a fantastic idea for the Santa canon it’s hard to believe that Rankin-Bass never did it.

Returning To Arthur Christmas was titled that because I’d left the subject for a couple weeks. You know how it gets. Here the discussion becomes more spoiler-y. And it has to address the question of what kind of straight line the reindeer might move in. There’s several possible answers and they’re all interesting.

Arthur Christmas And The Least Common Multiple supposes that reindeer move as way satellites do. By making some assumptions about the speed of the reindeer and the path they’re taking, I get to see how long Arthur and Grand-Santa would need to wait before the reindeer and sled are back if they’re lucky enough to be waiting on the equator.

Six Minutes Off makes the problem of Arthur and Grand-Santa waiting for the return of flying reindeer more realistic. This involves supposing that they’re not on the equator, which makes meeting up the reindeer a much nastier bit of timing. If they get unlucky it could make their rescue take over five thousand years, which would complicate the movie’s plot some.

And finally Arthur Christmas and the End of Time gets into one of those staggering thoughts. This would be recurrence, an idea that weaves into statistical mechanics and that seems to require that we accept how the conservation of energy and the fact of entropy are, together, a paradox. So we get into considerations of the long-term fate of the universe. Maybe.

Reading the Comics, December 16, 2017: Andertoons Drought Ended Edition


And now, finally, we get what we’ve been waiting so long for: my having enough energy and time to finish up last week’s comics. And I make excuses to go all fanboy over Elzie Segar’s great Thimble Theatre. Also more attention to Zach Weinersmith. You’ve been warned.

Mark Anderson’s Andertoons for the 13th is finally a breath of Mark Anderson’s Andertoons around here. Been far too long. Anyway it’s an algebra joke about x’s search for identity. And as often happens I’m sympathetic here. It’s not all that weird to think of ‘x’ as a label for some number. Knowing whether it means “a number whose value we haven’t found yet” or “a number whose value we don’t care about” is one trick, though. It’s not something you get used to from learning about, like, ‘6’. And knowing whether we can expect ‘x’ to have held whatever value it represented before, or whether we can expect it to be something different, is another trick.

Doug Bratton’s Pop Culture Shock Therapy for the 13th I feel almost sure has come up here before. Have I got the energy to find where? Oh, yes. It ran the 5th of September, 2015.

Buckles: Bark! ... Bark bark! ... Bark bark bark! ... (Dazzled.) 'It's difficult to bark sequentially when you don't know how to count.'
David Gilbert’s Buckles for the 14th of December, 2017. I quite like Buckles’s little off-put look in the final panel. It’s very dog considering the situation.

David Gilbert’s Buckles for the 14th is a joke on animals’ number sense. In fairness, after that start I wouldn’t know whether to go for four or five barks myself.

Hugo: 'Adding a long column of numbers is hard. Maybe it'll be easier if I write smaller. Then the column will be shorter.'
Bud Blake’s Tiger for the 15th of December, 2017. One of my love’s favorite recurring motifs in Peanuts is when Sally works out some ridiculous string of not-quite-reasoning and Charlie Brown just sits and watches and kind of stares at the reader through it. Tiger is definitely doing that same “… what?” look as Hugo figures out his strategy.

Bud Blake’s Tiger for the 15th is a bit of kid logic about how to make a long column of numbers easier to add. I endorse the plan of making the column shorter, although I’d do that by trying to pair up numbers that, say, add to 10 or 20 or something else easy to work with. Partial sums can make the overall work so much easier. And probably avoid mistakes.

Bunzo: 'You mean to say I was hit by just one man?' Referee: 'Yes, one man - you must get up, the count will soon be to ten. My gosh, General, you must get up - I'm running out of fractions. 8 19/20 - 9 - 9 1/25 - 9 2/25 - 9 3/25 --- ' Bunzo: 'Use hundredths.' (Getting up.) 'You rat! Everybody's laughing at me! Me, the great chief General!! You're not supposed to do me like this!' Popeye: 'Don't get sore, General. Come on, it's your turn to sock me.' Bunzo: 'Hold still so I can bust your chin.' Popeye: 'Okay, shoot.' Bunzo: 'That'll finish you!' (Smacking Popeye on the chin. It's not very effective.) Popeye: 'You should eat more spinach.' Bunzo: 'Great guns! Are you still standing?!!'
Elzie Segar’s Thimble Theatre for the 8th of July, 1931, and rerun the 15th of December, 2017. If I’m not missing, this week has included Popeye’s first claims about spinach providing him with superior strength. And I know you’re looking at the referee there and thinking J Wellington Wimpy. I’m not sure, since I haven’t checked the complete collection to read ahead in the story, but I think this is merely a proto-Wimpy. (Mind, the Wikipedia entry on this is a complete mess. Bud Sagendorf’s Popeye: The First Fifty Years says Wimpy was derived from a minor character in Segar’s earlier The Five-Fifteen strip, which would itself turn into Sappo. But that proto-Wimpy didn’t have much personality or even a name.)

Elzie Segar’s Thimble Theatre for the 8th of July, 1931, is my most marginal inclusion yet. It was either that strip or the previous day’s worth including. I’m throwing it in here because Segar’s Thimble Theatre keeps being surprisingly good. And, heck, slowing a count by going into fractions is viable way to do it. As the clobbered General Bunzo points out, you can drag this out longer by going into hundredths. Or smaller units. There is no largest real number less than ten; if it weren’t incredibly against the rules, boxers could make use of that.

Zach Weinersmith’s Saturday Morning Breakfast Cereal for the 15th is about those mathematics problems with clear and easy-to-understand statements whose answers defy intuition. Weinersmith is completely correct about all of this. I’m surprised he doesn’t mention the one about how you could divide an orange into five pieces, reassemble the pieces, and get back two spheres each the size of a sun.

Reading the Comics, December 11, 2017: Vamping For Andertoons Edition


So Mark Anderson’s Andertoons has been missing from the list of mathematically-themed the last couple weeks. Don’t think I haven’t been worried about that. But it’s finally given another on-topic-enough strip and I’m not going to include it here. I’ve had a terrible week and I’m going to use the comics we got in last week slowly.

Hector D Cantu and Carlos Castellanos’s Baldo for the 10th of December uses algebra as the type for homework you’d need help with. It reads plausibly enough to me, at least so far as I remember learning algebra.

Greg Evans’s Luann Againn for the 10th reprints the strip of the 10th of December, 1989. And as often happens, mathematics is put up as the stuff that’s too hard to really do. The expressions put up don’t quite parse; there’s nothing to solve. But that’s fair enough for a panicked brain. To not recognize what the problem even is makes it rather hard to solve.

Ruben Bolling’s Super-Fun-Pak Comix for the 10th is an installation of Quantum Mechanic, playing on the most fun example of non-commutative processes I know. That’s the uncertainty principle, which expresses itself as pairs of quantities that can’t be precisely measured simultaneously. There are less esoteric kinds of non-commutative processes. Like, rotating something 90 degrees along a horizontal and then along a vertical axis will turn stuff different from 90 degrees vertical and then horizontal. But that’s too easy to understand to capture the imagination, at least until you’re as smart as an adult and as thoughtful as a child.

Maria Scrivan’s Half Full for the 11th features Albert Einstein and one of the few equations that everybody knows. So that’s something.

Jeff Stahler’s Moderately Confused for the 11th features the classic blackboard full of equations, this time to explain why Christmas lights wouldn’t work. There is proper mathematics in lights not working. It’s that electrical-engineering work about the flow of electricity. The problem is, typically, a broken or loose bulb. Maybe a burnt-out fuse, although I have never fixed a Christmas lights problem by replacing the fuse. It’s just something to do so you can feel like you’ve taken action before screaming in rage and throwing the lights out onto the front porch. More interesting to me is the mathematics of strands getting tangled. The idea — a foldable thread, marked at regular intervals by points that can hook together — seems trivially simple. But it can give insight into how long molecules, particularly proteins, will fold together. It may help someone frustrated to ponder that their light strands are knotted for the same reasons life can exist. But I’m not sure it ever does.

What You Need To Pass This Class. Also: It’s Algebra, Uncle Fletcher


The end of the (US) semester snuck up on me but, in my defense, I’m not teaching this semester. If you know someone who needs me to teach, please leave me a note. But as a service for people who are just trying to figure out exactly how much studying they need to do for their finals, knock it off. You’re not playing a video game. It’s not like you can figure out how much effort it takes to get an 83.5 on the final and then put the rest of your energy into your major’s classes.

But it’s a question people ask, and keep asking, so here’s my answers. This essay describes exactly how to figure out what you need, given whatever grade you have and whatever extra credit you have and whatever the weighting of the final exam is and all that. That might be more mechanism than you need. If you’re content with an approximate answer, here’s some tables for common finals weightings, and a selection of pre-final grades.

For those not interested in grade-grubbing, here’s some old-time radio. Vic and Sade was a longrunning 15-minute morning radio program written with exquisite care by Paul Rhymer. It’s not going to be to everyone’s taste. But if it is yours, it’s going to be really yours: a tiny cast of people talking not quite past one another while respecting the classic Greek unities. Part of the Overnightscape Underground is the Vic and Sadecast, which curates episodes of the show, particularly trying to explain the context of things gone by since 1940. This episode, from October 1941, is aptly titled “It’s Algebra, Uncle Fletcher”. Neither Vic nor Sade are in the episode, but their son Rush and Uncle Fletcher are. And they try to work through high school algebra problems. I’m tickled to hear Uncle Fletcher explaining mathematics homework. I hope you are too.

Reading the Comics, December 9, 2017: Zach Weinersmith Wants My Attention Edition


If anything dominated the week in mathematically-themed comic strips it was Zach Weinersmith’s Saturday Morning Breakfast Cereal. I don’t know how GoComics selects the strips to (re?)print on their site. But there were at least four that seemed on-point enough for me to mention. So, okay. He’s got my attention. What’s he do with it?

On the 3rd of December is a strip I can say is about conditional probability. The mathematician might be right that the chance someone will be murdered by a serial killer are less than one in ten million. But that is the chance of someone drawn from the whole universe of human experiences. There are people who will never be near a serial killer, for example, or who never come to his attention or who evade his interest. But if we know someone is near a serial killer, or does attract his interest? The information changes the probability. And this is where you get all those counter-intuitive and somewhat annoying logic puzzles about, like, the chance someone’s other child is a girl if the one who just walked in was, and how that changes if you’re told whether the girl who just entered was the elder.

On the 5th is a strip about sequences. And built on the famous example of exponential growth from doubling a reward enough times. Well, you know these things never work out for the wise guy. The “Fibonacci Spiral” spoken of in the next-to-last panel is a spiral, like you figure. The dimensions of the spiral are based on those of golden-ratio rectangles. It looks a great deal like a logarithmic spiral to the untrained eye. Also to the trained eye, but you knew that. I think it’s supposed to be humiliating that someone would call such a spiral “random”. But I admit I don’t get that part.

The strip for the 6th has a more implicit mathematical content. It hypothesizes that mathematicians, given the chance, will be more interested in doing recreational puzzles than even in eating and drinking. It’s amusing, but I’ll admit I’ve found very few puzzles all that compelling. This isn’t to say there aren’t problems I keep coming back to because I’m curious about them, just that they don’t overwhelm my common sense. Don’t ask me when I last received actual pay for doing something mathematical.

And then on the 9th is one more strip, about logicians. And logic puzzles, such as you might get in a Martin Gardner collection. The problem is written out on the chalkboard with some shorthand logical symbols. And they’re symbols both philosophers and mathematicians use. The letter that looks like a V with a crossbar means “for all”. (The mnemonic I got was “it’s an A-for-all, upside-down”. This paired with the other common symbol, which looks like a backwards E and means there exists: “E-for-exists, backwards”. Later I noticed upside-down A and backwards E could both be just 180-degree-rotated A and E. But try saying “180-degree-rotated” in a quick way.) The curvy E between the letters ‘x’ and ‘S’ means “belongs to the set”. So that first line says “for all x that belong to the set S this follows”. Writing out “isLiar(x)” instead of, say, “L(x)”, is more a philosopher’s thing than a mathematician’s. But it wouldn’t throw anyway. And the T just means emphasizing that this is true.

And that is as much about Saturday Morning Breakfast Cereal as I have to say this week.

Sam Hurt’s Eyebeam for the 4th tells a cute story about twins trying to explain infinity to one another. I’m not sure I can agree with the older twin’s assertion that infinity means there’s no biggest number. But that’s just because I worry there’s something imprecise going on there. I’m looking forward to the kids learning about negative numbers, though, and getting to wonder what’s the biggest negative real number.

Percy Crosby’s Skippy for the 4th starts with Skippy explaining a story problem. One about buying potatoes, in this case. I’m tickled by how cranky Skippy is about boring old story problems. Motivation is always a challenge. The strip originally ran the 7th of October, 1930.

Dave Whamond’s Reality Check for the 6th uses a panel of (gibberish) mathematics as an example of an algorithm. Algorithms are mathematical, in origin at least. The word comes to us from the 9th century Persian mathematician Al-Khwarizmi’s text about how to calculate. The modern sense of the word comes from trying to describe the methods by which a problem can be solved. So, legitimate use of mathematics to show off the idea. The symbols still don’t mean anything.

Joe: 'Grandpa, what's 5x7?' Grandpa: 'Why do you wanna know?' Joe: 'I'm testing your memory.' Grandpa: 'Oh! The answer's 35.' Joe: 'Thanks! Now what is 8x8?' Grandpa: 'Joe, is that last night's homework?' Joe: 'We're almost done! Only 19 more!'
Rick Detorie’s One Big Happy for the 7th of December, 2017. And some attention, please, for Ruthie there. She’s completely irrelevant to the action, but it makes sense for her to be there if Grandpa is walking them to school, and she adds action — and acting — to the scenes.

Rick Detorie’s One Big Happy for the 7th has Joe trying to get his mathematics homework done at the last minute. … And it’s caused me to reflect on how twenty multiplication problems seems like a reasonable number to do. But there’s only fifty multiplications to even do, at least if you’re doing the times tables up to the 10s. No wonder students get so bored seeing the same problems over and over. It’s a little less dire if you’re learning times tables up to the 12s, but not that much better. Yow.

Olivia Walch’s Imogen Quest for the 8th looks pretty legitimate to me. It’s going to read as gibberish to people who haven’t done parametric functions, though. Start with the plane and the familiar old idea of ‘x’ and ‘y’ representing how far one is along a horizontal and a vertical direction. Here, we’re given a dummy variable ‘t’, and functions to describe a value for ‘x’ and ‘y’ matching each value of ‘t’. The plot then shows all the points that ever match a pair of ‘x’ and ‘y’ coordinates for some ‘t’. The top drawing is a shape known as the cardioid, because it kind of looks like a Valentine-heart. The lower figure is a much more complicated parametric equation. It looks more anatomically accurate,

Still no sign of Mark Anderson’s Andertoons and the drought is worrying me, yes.

But they’re still going on the cartoonist’s web site, so there’s that.

As I Try To Make Wronski’s Formula For Pi Into Something I Like


Previously:

I remain fascinated with Józef Maria Hoëne-Wronski’s attempted definition of π. It had started out like this:

\pi = \frac{4\infty}{\sqrt{-1}}\left\{ \left(1 + \sqrt{-1}\right)^{\frac{1}{\infty}} -  \left(1 - \sqrt{-1}\right)^{\frac{1}{\infty}} \right\}

And I’d translated that into something that modern mathematicians would accept without flinching. That is to evaluate the limit of a function that looks like this:

\displaystyle \lim_{x \to \infty} f(x)

where

f(x) = -4 \imath x \left\{ \left(1 + \imath\right)^{\frac{1}{x}} -  \left(1 - \imath\right)^{\frac{1}{x}} \right\}

So. I don’t want to deal with that f(x) as it’s written. I can make it better. One thing that bothers me is seeing the complex number 1 + \imath raised to a power. I’d like to work with something simpler than that. And I can’t see that number without also noticing that I’m subtracting from it 1 - \imath raised to the same power. 1 + \imath and 1 - \imath are a “conjugate pair”. It’s usually nice to see those. It often hints at ways to make your expression simpler. That’s one of those patterns you pick up from doing a lot of problems as a mathematics major, and that then look like magic to the lay audience.

Here’s the first way I figure to make my life simpler. It’s in rewriting that 1 + \imath and 1 - \imath stuff so it’s simpler. It’ll be simpler by using exponentials. Shut up, it will too. I get there through Gauss, Descartes, and Euler.

At least I think it was Gauss who pointed out how you can match complex-valued numbers with points on the two-dimensional plane. On a sheet of graph paper, if you like. The number 1 + \imath matches to the point with x-coordinate 1, y-coordinate 1. The number 1 - \imath matches to the point with x-coordinate 1, y-coordinate -1. Yes, yes, this doesn’t sound like much of an insight Gauss had, but his work goes on. I’m leaving it off here because that’s all that I need for right now.

So these two numbers that offended me I can think of as points. They have Cartesian coordinates (1, 1) and (1, -1). But there’s never only one coordinate system for something. There may be only one that’s good for the problem you’re doing. I mean that makes the problem easier to study. But there are always infinitely many choices. For points on a flat surface like a piece of paper, and where the points don’t represent any particular physics problem, there’s two good choices. One is the Cartesian coordinates. In it you refer to points by an origin, an x-axis, and a y-axis. How far is the point from the origin in a direction parallel to the x-axis? (And in which direction? This gives us a positive or a negative number) How far is the point from the origin in a direction parallel to the y-axis? (And in which direction? Same positive or negative thing.)

The other good choice is polar coordinates. For that we need an origin and a positive x-axis. We refer to points by how far they are from the origin, heedless of direction. And then to get direction, what angle the line segment connecting the point with the origin makes with the positive x-axis. The first of these numbers, the distance, we normally label ‘r’ unless there’s compelling reason otherwise. The other we label ‘θ’. ‘r’ is always going to be a positive number or, possibly, zero. ‘θ’ might be any number, positive or negative. By convention, we measure angles so that positive numbers are counterclockwise from the x-axis. I don’t know why. I guess it seemed less weird for, say, the point with Cartesian coordinates (0, 1) to have a positive angle rather than a negative angle. That angle would be \frac{\pi}{2} , because mathematicians like radians more than degrees. They make other work easier.

So. The point 1 + \imath corresponds to the polar coordinates r = \sqrt{2} and \theta = \frac{\pi}{4} . The point 1 - \imath corresponds to the polar coordinates r = \sqrt{2} and \theta = -\frac{\pi}{4} . Yes, the θ coordinates being negative one times each other is common in conjugate pairs. Also, if you have doubts about my use of the word “the” before “polar coordinates”, well-spotted. If you’re not sure about that thing where ‘r’ is not negative, again, well-spotted. I intend to come back to that.

With the polar coordinates ‘r’ and ‘θ’ to describe a point I can go back to complex numbers. I can match the point to the complex number with the value given by r e^{\imath\theta} , where ‘e’ is that old 2.71828something number. Superficially, this looks like a big dumb waste of time. I had some problem with imaginary numbers raised to powers, so now, I’m rewriting things with a number raised to imaginary powers. Here’s why it isn’t dumb.

It’s easy to raise a number written like this to a power. r e^{\imath\theta} raised to the n-th power is going to be equal to r^n e^{\imath\theta \cdot n} . (Because (a \cdot b)^n = a^n \cdot b^n and we’re going to go ahead and assume this stays true if ‘b’ is a complex-valued number. It does, but you’re right to ask how we know that.) And this turns into raising a real-valued number to a power, which we know how to do. And it involves dividing a number by that power, which is also easy.

And we can get back to something that looks like 1 + \imath too. That is, something that’s a real number plus \imath times some real number. This is through one of the many Euler’s Formulas. The one that’s relevant here is that e^{\imath \phi} = \cos(\phi) + \imath \sin(\phi) for any real number ‘φ’. So, that’s true also for ‘θ’ times ‘n’. Or, looking to where everybody knows we’re going, also true for ‘θ’ divided by ‘x’.

OK, on to the people so anxious about all this. I talked about the angle made between the line segment that connects a point and the origin and the positive x-axis. “The” angle. “The”. If that wasn’t enough explanation of the problem, mention how your thinking’s done a 360 degree turn and you see it different now. In an empty room, if you happen to be in one. Your pedantic know-it-all friend is explaining it now. There’s an infinite number of angles that correspond to any given direction. They’re all separated by 360 degrees or, to a mathematician, 2π.

And more. What’s the difference between going out five units of distance in the direction of angle 0 and going out minus-five units of distance in the direction of angle -π? That is, between walking forward five paces while facing east and walking backward five paces while facing west? Yeah. So if we let ‘r’ be negative we’ve got twice as many infinitely many sets of coordinates for each point.

This complicates raising numbers to powers. θ times n might match with some point that’s very different from θ-plus-2-π times n. There might be a whole ring of powers. This seems … hard to work with, at least. But it’s, at heart, the same problem you get thinking about the square root of 4 and concluding it’s both plus 2 and minus 2. If you want “the” square root, you’d like it to be a single number. At least if you want to calculate anything from it. You have to pick out a preferred θ from the family of possible candidates.

For me, that’s whatever set of coordinates has ‘r’ that’s positive (or zero), and that has ‘θ’ between -π and π. Or between 0 and 2π. It could be any strip of numbers that’s 2π wide. Pick what makes sense for the problem you’re doing. It’s going to be the strip from -π to π. Perhaps the strip from 0 to 2π.

What this all amounts to is that I can turn this:

f(x) = -4 \imath x \left\{ \left(1 + \imath\right)^{\frac{1}{x}} -  \left(1 - \imath\right)^{\frac{1}{x}} \right\}

into this:

f(x) = -4 \imath x \left\{ \left(\sqrt{2} e^{\imath \frac{\pi}{4}}\right)^{\frac{1}{x}} -  \left(\sqrt{2} e^{-\imath \frac{\pi}{4}} \right)^{\frac{1}{x}} \right\}

without changing its meaning any. Raising a number to the one-over-x power looks different from raising it to the n power. But the work isn’t different. The function I wrote out up there is the same as this function:

f(x) = -4 \imath x \left\{ \sqrt{2}^{\frac{1}{x}} e^{\imath \frac{\pi}{4}\cdot\frac{1}{x}} - \sqrt{2}^{\frac{1}{x}} e^{-\imath \frac{\pi}{4}\cdot\frac{1}{x}} \right\}

I can’t look at that number, \sqrt{2}^{\frac{1}{x}} , sitting there, multiplied by two things added together, and leave that. (OK, subtracted, but same thing.) I want to something something distributive law something and that gets us here:

f(x) = -4 \imath x \sqrt{2}^{\frac{1}{x}} \left\{ e^{\imath \frac{\pi}{4}\cdot\frac{1}{x}} -  e^{- \imath \frac{\pi}{4}\cdot\frac{1}{x}} \right\}

Also, yeah, that square root of two raised to a power looks weird. I can turn that square root of two into “two to the one-half power”. That gets to this rewrite:

f(x) = -4 \imath x 2^{\frac{1}{2}\cdot \frac{1}{x}} \left\{ e^{\imath \frac{\pi}{4}\cdot\frac{1}{x}} -  e^{- \imath \frac{\pi}{4}\cdot\frac{1}{x}} \right\}

And then. Those parentheses. e raised to an imaginary number minus e raised to minus-one-times that same imaginary number. This is another one of those magic tricks that mathematicians know because they see it all the time. Part of what we know from Euler’s Formula, the one I waved at back when I was talking about coordinates, is this:

\sin\left(\phi\right) = \frac{e^{\imath \phi} - e^{-\imath \phi}}{2\imath }

That’s good for any real-valued φ. For example, it’s good for the number \frac{\pi}{4}\cdot\frac{1}{x} . And that means we can rewrite that function into something that, finally, actually looks a little bit simpler. It looks like this:

f(x) = -2 x 2^{\frac{1}{2}\cdot \frac{1}{x}} \sin\left(\frac{\pi}{4}\cdot \frac{1}{x}\right)

And that’s the function whose limit I want to take at ∞. No, really.

How November 2017 Treated My Mathematics Blog


I was barely done sulking about the drop in readership on my humor blog when I started preparing the mathematics-blog readership report. And readership did drop from October (and September). Not by much, though. There were 1,052 pages viewed here in November 2017, barely less than October’s 1,069. It’s a fair bit under September’s 1,232, but that’s to be expected when I don’t have a strong gimmick going on like an A To Z project.

The number of unique visitors dropped, down to 604 from October’s 614, again a trivial difference. September had seen 672 visitors and that’s a more noticeable drop. Still not much, considering. The number of likes rose a bit, up to 70 from October’s 64. Still down from September’s 98. And all that still way down from, like, a year ago. I don’t know if it’s my shuffling off into irrelevance or if there’s something making likes less of a thing lately. I’d be curious other bloggers’ experience.

I’d started December with 55,419 page views from an estimated 25,617 known unique visitors, although some of them I only know apart because of their nametags.

So what countries have sent me readers? 56 of them, up from October’s 51 but down from September’s 65. How many sent me multiple readers? All but 22 of those. That’s up from October — 13 single-reader countries — and September — 20 single-reader countries — but these things happen. Here’s the full roster:

Country Readers
United States 676
United Kingdom 87
Canada 46
India 40
Philippines 26
Australia 15
Singapore 11
Brazil 9
Spain 9
Bangladesh 8
Hong Kong SAR China 7
Belgium 6
Germany 6
Israel 6
Slovenia 6
Uruguay 6
European Union 5
France 5
South Africa 5
South Korea 5
Switzerland 5
Denmark 4
Italy 4
Sweden 4
Egypt 3
Iceland 3
Indonesia 3
Netherlands 3
Austria 2
Ireland 2
Lithuania 2
Poland 2
Qatar 2
United Arab Emirates 2
Algeria 1
Argentina 1
Azerbaijan 1
Estonia 1
Ethiopia 1
Japan 1 (*)
Kazakhstan 1
Kuwait 1
Lebanon 1
Maldives 1
Mexico 1
Norway 1
Oman 1
Peru 1
Portugal 1
Romania 1
Saudi Arabia 1
Slovakia 1
St. Kitts and Nevis 1
Thailand 1
Tunisia 1
Zimbabwe 1

Japan’s the only country to have sent me a single reader last month too, and no countries have sent me single readers more than two months in a row currently.

So that’s general popularity. What articles were popular around here? One traditional piece. Reading the Comics pieces. And the lovably misguided attempt by Józef Maria Hoëne-Wronski to give us a culturally neutral definition of π broke out to … well, second and third place, anyway:

Also, clearly, I need to think of more simple mathematically-answerable questions that everybody wonders since that record-side question is always popular. And when that is less popular, the question about how many kinds of trapezoid there are turns up.

Anyway, should you have read this and decided you want to be among my hundreds of WordPress followers who somehow don’t show up on the readership statistics, please, do so. There should be a ‘Follow on WordPress’ button in the upper right corner of the page. There’s also a ‘Follow by e-mail’ if you want things sent to an already-overfull box of things you haven’t time to read. Thank you.

Reading the Comics, December 2, 2017: Showing Intelligence Edition


November closed out with another of those weeks not quite busy enough to justify splitting into two. I blame Friday and Saturday. Nothing mathematically-themed was happening them. Suppose some days are just like that.

Johnny Hart’s Back To BC for the 26th is an example of using mathematical truths as profound statements. I’m not sure that I’d agree with just stating the Pythagorean Theorem as profound, though. It seems like a profound statement has to have some additional surprising, revelatory elements to it. Like, knowing the Pythagorean theorem is true means we can prove there’s exactly one line parallel to a given line and passing through some point. Who’d see that coming? I don’t blame Hart for not trying to fit all that into one panel, though. Too slow a joke. The strip originally ran the 4th of September, 1960.

Tom Toles’s Randolph Itch, 2 am rerun for the 26th is a cute little arithmetic-in-real-life panel. I suppose arithmetic-in-real-life. Well, I’m amused and stick around for the footer joke. The strip originally ran the 24th of February, 2002.

Zach Weinersmith’s Saturday Morning Breakfast Cereal makes its first appearance for the week on the 26th. It’s an anthropomorphic-numerals joke and some wordplay. Interesting trivia about the whole numbers that never actually impresses people: a whole number is either a perfect square, like 1 or 4 or 9 or 16 are, or else its square root is irrational. There’s no whole number with a square root that’s, like, 7.745 or something. Maybe I just discuss it with people who’re too old. It seems like the sort of thing to reveal to a budding mathematician when she’s eight.

Saturday Morning Breakfast Cereal makes another appearance the 29th. The joke’s about using the Greek ε, which has a long heritage of use for “a small, positive number”. We use this all the time in analysis. A lot of proofs in analysis are done by using ε in a sort of trick. We want to show something is this value, but it’s too hard to do. Fine. Pick any ε, a positive number of unknown size. So then we’ll find something we can calculate, and show that the difference between the thing we want and the thing we can do is smaller than ε. And that the value of the thing we can calculate is that. Therefore, the difference between what we want and what we can do is smaller than any positive number. And so the difference between them must be zero, and voila! We’ve proved what we wanted to prove. I have always assumed that we use ε for this for the association with “error”, ideally “a tiny error”. If we need another tiny quantity we usually go to δ, probably because it’s close to ε and ‘d’ is still a letter close to ‘e’. (The next letter after ε is ζ, which carries other connotations with it and is harder to write than δ is.) Anyway, Weinersmith is just doing a ha-ha, your penis is small joke.

Samson’s Dark Side of the Horse for the 28th is a counting-sheep joke. It maybe doesn’t belong here but I really, really like the art of the final panel and I want people to see it.

Arnoldine: 'If you're so SMART, what's the SQUARE ROOT of a million?!' Arnold, after a full panel's thought: 'FIVE!' Arnoldine: 'OK! What's the square root of TWO MILLION?!'
Bud Grace’s Piranha Club for the 29th of November, 2017. So do always remember the old advice for attorneys and people doing investigative commissions: never ask a question you don’t already know the answer to.

Bud Grace’s Piranha Club for the 29th is, as with Back to BC, an attempt at showing intelligence through mathematics. There are some flaws in the system. Fun fact: since one million is a perfect square, Arnold could have answered within a single panel. (Also fun fact: I am completely unqualified to judge whether something is a “fun” fact.)

Jason Chatfield’s Ginger Meggs for the 29th is Ginger subverting the teacher’s questions, like so many teacher-and-student jokes will do.

Dan Thompson’s Brevity for the 30th is the anthropomorphic geometric figures joke for the week.

There seems to be no Mark Anderson’s Andertoons for this week. There’ve been some great ones (like on the 26th or the 28th and the 29th) but they’re not at all mathematical. I apologize for the inconvenience and am launching an investigation into this problem.

Deciphering Wronski, Non-Standardly


I ran out of time to do my next bit on Wronski’s attempted definition of π. Next week, all goes well. But I have something to share anyway. William Lane Craig, of the The author of Boxing Pythagoras blog was intrigued by the starting point. And as a fan of studying how people understand infinity and infinitesimals (and how they don’t), this two-century-old example of mixing the numerous and the tiny set his course.

So here’s his essay, trying to work out Wronski’s beautiful weird formula from a non-standard analysis perspective. Non-standard analysis is a field that’s grown in the last fifty years. It’s probably fairly close in spirit to what (I think) Wronski might have been getting at, too. Non-standard analysis works with ideas that seem to match many people’s intuitive feelings about infinitesimals and infinities.

For example, can we speak of a number that’s larger than zero, but smaller than the reciprocal of any positive integer? It’s hard to imagine such a thing. But what if we can show that if we suppose such a number exists, then we can do this logically sound work with it? If you want to say that isn’t enough to show a number exists, then I have to ask how you know imaginary numbers or negative numbers exist.

Standard analysis, you probably guessed, doesn’t do that. It developed over the 19th century when the logical problems of these kinds of numbers seemed unsolvable. Mostly that’s done by limits, showing that a thing must be true whenever some quantity is small enough, or large enough. It seems safe to trust that the infinitesimally small is small enough, and the infinitely large is large enough. And it’s not like mathematicians back then were bad at their job. Mathematicians learned a lot of things about how infinitesimals and infinities work over the late 19th and early 20th century. It makes modern work possible.

Anyway, Boxing Pythagoras goes over what a non-standard analysis treatment of the formula suggests. I think it’s accessible even if you haven’t had much non-standard analysis in your background. At least it worked for me and I haven’t had much of the stuff. I think it’s also accessible if you’re good at following logical argument and won’t be thrown by Greek letters as variables. Most of the hard work is really arithmetic with funny letters. I recommend going and seeing if he did get to π.