Euler’s number pops up in situations that involve optimality

https://www.quantamagazine.org/why-eulers-number-is-just-the-best-20211124/

by elsewhen • 5 years ago

135 95 5 years ago

If you want to go deeper, Eli Maor's "e: The Story of a Number" [0] is a great read that doesn't shy away from showing a few equations.

[0] https://press.princeton.edu/books/paperback/9780691168487/e-...

vesinisa• 5 years ago

Title should be edited to lowercase e for Euler's number.

mromanuk• 5 years ago

Yes:

Why Euler's number (e), the Transcendental Math Constant, Is Just the Best

adunk3• 5 years ago

For everyone that, like me, like to read only the headline and then proceed directly into the comments:

The title of the link currently is "Why E, the Transcendental Math Constant, Is Just the Best".

But the article really is about Euler's constant - the lower case e - and not about any of the capital E:s out there (like the capital E sometimes used in scientific notation, or the expected value in probability theory).

corndoge• 5 years ago

Are either of the latter transcendental constants

lordnacho2• 5 years ago

See what happens when you're so smart you get multiple things named after you?

This is not the e you know and love from school: https://en.wikipedia.org/wiki/Euler%27s_constant

This one is: https://en.wikipedia.org/wiki/E_(mathematical_constant)

Worth coming up with some better way to talk about this.

poizan422• 5 years ago

The first one is usually (at least from what I've seen) called the Euler–Mascheroni constant which is denoted by γ, so I don't think there is much confusion.

ianai5• 5 years ago

Euler was much more than smart. The man went home during the Black Plague and studied math so hard he went blind in one eye - presumably so his brain could use those neurons for math instead of sight. He was also discredited in his time and for centuries after for an intuitive understanding of calculus through infinitesimal and infinite numbers - which was only relatively recently put into rigor akin to epsilon-delta calculus. Also considered the last person to be able to know all of the known world of mathematics at his point in time.

I kind of wish we had a holiday of some kind to appreciate either Euler himself or even a month to discuss the historical contributions to knowledge by philosophers and scientists alike.

st_goliath• 5 years ago

See what happens when you're so smart you get multiple things named after you?

Yes, this problem is touched on in the Wikipedia "List of Things named after Leonhard Euler" (https://en.wikipedia.org/wiki/List_of_things_named_after_Leo...)

I particularly like the remark in the introduction:

In an effort to avoid naming everything after Euler, some discoveries and theorems are attributed to the first person to have proved them after Euler.

jamespwilliams• 5 years ago

This was probably the result of HN's autocapitalisation of post titles. The title of the article itself uses lowercase e. In any case, the title has been changed now.

throwaway81523• 5 years ago

Yeah the title almost seemed like clickbait since "Euler's constant" usually means γ=0.5772... provoking a reaction of "where does that show up in optimization?". That the constant turned out to be e=2.718... which shows up all over the place was a big disappointment

nick__m• 5 years ago

And my favorite equation is ℇ^(ⅈπ)+1=0 !

It contains Euler, the imaginary unit, the unit, the zero and some hidden trigonometry.

P.S. does anyone know why the unicode symbol for the Euler constant render as a weird E when it is usually represented as a slightly italicized e ?

mkl• 5 years ago

Also π and the three most important operations: addition, multiplication, exponentiation.

3232• 5 years ago

addition, multiplication, exponentiation.

Which are the hyperoperations of rank 1, 2 and 3:

In mathematics, the hyperoperation sequence is an infinite sequence of arithmetic operations (called hyperoperations in this context) that starts with a unary operation (the successor function with n = 0). The sequence continues with the binary operations of addition (n = 1), multiplication (n = 2), and exponentiation (n = 3).

https://en.wikipedia.org/wiki/Hyperoperation

adunk3• 5 years ago

One of the things I really like about the tau manifesto (the proposal to use tau == 2 * pi instead of pi in many situations) was their explanation of how tau made this equation all the more interesting (IMHO) by making it "almost like a tautology":

https://tauday.com/tau-manifesto#sec-euler_s_identity

janto• 5 years ago

Indeed. It shows that the pi formulation is actually somewhat ugly because it lacks symmetry.

Scarblac• 5 years ago

The weird E is Euler's _constant_, and the slightly italicized e is Euler's _number_.

https://en.wikipedia.org/wiki/Euler%27s_constant https://en.wikipedia.org/wiki/E_(mathematical_constant)

poizan422• 5 years ago

But that is the Euler–Mascheroni constant which is normally denoted by gamma.

There is a footnote on https://en.wikipedia.org/wiki/Letterlike_Symbols that says:

It's unknown which constant this is supposed to be. Xerox standard XCCS 353/046 just says 'Euler's'.

See also this discussion on math stackexchange: https://math.stackexchange.com/a/3123704

f00zz2• 5 years ago

This follows from e^(ix) = cos(x) + i sin(x)! I'm currently reading the Qiskit quantum computing textbook, and the appendix on linear algebra has a demonstration: https://qiskit.org/textbook/ch-appendix/linear_algebra.html

sidpatil• 5 years ago

And that follows from De Moivre's formula, (cos(x)+ i sin(x))^n = cos(nx) + i sin(nx).

https://en.wikipedia.org/wiki/De_Moivre%27s_formula

wrycoder• 5 years ago

Which only slightly obfuscates the fact that e^(iπ) = -1. Bamboozles the rubes!

3232• 5 years ago

e^(iπ) = -1 is basically the unit circle in the complex plane:

https://en.wikipedia.org/wiki/Circle_group

_Microft• 5 years ago

I wonder how many mathematicians and physicists were harmed by the submitted title ;)

(I would like to increase the count by e^0 btw)

ReleaseCandidat2• 5 years ago

Mathematician. Thought about a new (at least to me) transcendental number ...

ReleaseCandidat2• 5 years ago

I prefer the Champernowne constant.

vmilner2• 5 years ago

Tim Gowers uses the differentiation of e^x as an example of something bright UK maths A-level students often don't understand fully:

https://gowers.wordpress.com/2012/11/20/what-maths-a-level-d...

londons_explore2• 5 years ago

It's because most exams and curriculums in the UK are so strictly defined that all questions are almost guaranteed to follow one of a small set of structures.

And schools have figured out that rather than teaching the subject from first principles, it's easier to get students to get high grades by teaching them each of the structures. Eg. "Whenever there is a question about differentiating x^7, just put 7x^6 as the answer." They then get the students to try a few examples (x^3 becomes 3x^2, x^77 becomes 77x^76, etc), and thats the way every science-y subject is taught.

I often think it leads to students who do well in exams, but can't solve many real world problems.

It could be solved by having a part of every exam paper be never-seen-before applied problems. For example, for differentiation, one might ask "A road's height in meters as a function of the horizontal distance along the road in kilometers is defined as sin(x)cos(x)tan(x). At what points are the steepest uphills? Would you describe the slope of the road as 'very hilly', and why?"

eigenket2• 5 years ago

I've seen pretty bright seeming UK university applicants able to do whatever you ask them but then completely shit the bed when you ask them to differentiate e^y with respect to y rather than e^x with respect to x.

dan-robertson2• 5 years ago

I think the problem is they want calculus in the curriculum and it is too late to be able to put it in context. There are some great uses for calculus that are accessible to many high school students. In particular, with physics you usually learn about capacitors and nuclear decay. Both of these cases are basically solving the differential equation y' = ky but:

- the physics course can’t depend on the concurrent maths course because you are allowed to take physics without taking maths, so you just learn weird equations full of exponential a instead of the ODE

- I think the maths course doesn’t even teach differential equations. They are in FP1 (from a separate ‘further maths’ course) but definitely not in AS (penultimate year of school) maths. Possibly a few turn up in A2 (final year) but then they can’t have any good examples from physics because not everyone doing maths will be able to depend on knowledge about what a capacitor is or how nuclear decay works. But I guess population models might work.

- there can be some better stuff in the further maths course (e.g. I think they might even have the ‘exponentiate a matrix’ solution to systems of first order linear ODEs)

scythe• 5 years ago

I was expecting this to happen because the proof that the limit at zero of (e^h - 1)/h = 1 is tricky — nope, the student doesn't recognize the derivative formula in the first place.

Aardwolf2• 5 years ago

The particular topics he wanted me to cover were integrating log x, or ln x as he called it

What's wrong with calling it ln x? The way this is written in the article implies there's something weird about calling it that. The name 'log' can mean log2, log10 or natural logarithm depending on the field.

Removing ambiguities from math notation should be considered a good thing.

The author expressed a worry about math education. Consider that a clear non ambiguous notation would help.

dan-robertson2• 5 years ago

Most mathematicians use log to mean either natural log, or sometimes log in the relevant base (e.g. 2 if you are talking about information theory).

In school (and engineering or physics I guess) you often are made to use ln for natural log and you are taught a way to pronounce that name (somewhere between lun and l’n)

It feels like the point is “this person had not been exposed to university style mathematics”.

yellowcake0• 5 years ago

The ln notation has gone out of fashion with mathematicians. Generally the base is clear from the context, or it's irrelevant.

As someone who has done a lot of mathematics in their life, I've never found this perceived ambiguity to be an issue.

tomrod• 5 years ago

This article reminded me of my maths journey. I was mechanically dutiful as a student, and would make lateral connections but had a lot of patchwork understanding. It wasn't until I understood the derivations in Real Analysis that things started to click.

alexilliamson• 5 years ago

Yes exactly! Deriving calculus from set axioms truly opened my mind to math, and more generally critical thinking.

Aerroon• 5 years ago

I think the reason for this is that derivation from 'first principles' isn't really done. You'll do it once or twice in the intro to derivatives and that's it. The other 40 hours you spend on derivatives won't even touch it.

The issue with being able to derive the formulas for derivation yourself is that it's not very useful. You simply don't have time to make those derivations during a test. It's like trying to use grammar rules in a conversation - conversations happen at a pace where you cannot apply grammar rules. You'll just have to know the patterns.

You learn things in school to do a test. The usefulness of the vast majority of the knowledge they attain is purely to help them do the test. Later in life you might wish you knew more about this or that, but that's not at all apparent to the student.

mabbo• 5 years ago

I had a wonderful grade 12 calc teacher in high school who taught everything from first principles. I would leave his class feeling like I had gone to the gym from my brain. Despite his incredible teaching, I only pulled off a low 70s grade in the class.

So I retook the course the next year. Taught by a new teacher fresh from teachers college, theoretically with a specialty in math since they were teaching an upper level math course.

I don't think the new teacher even knew how to do derivatives from first principles. Just rote memorization of the different types of differentiation.

I got an A in that class the second time, having learned nothing.

vmilner2• 5 years ago

[I should add that this was posted in 2012, and differentiation from first principles was apparently emphasised far more in the syllabus in 2017 onwards.]

DeathArrow• 5 years ago

I find this beautiful:

e^iπ = −1

montroser• 5 years ago

Yeah! Which of course also means that e and π can be defined in terms of one another.

dotancohen• 5 years ago

That is probably the most insightful thing I've read all year. I wonder if there are any subtle implications.

jstx14• 5 years ago

The more general formula (e^ix = cosx + i*sinx) looks better to me because it defines exponentiation of a complex number as a rotation around a unit circle. It has a nice proof, some cool visualisations and a lot of implications to a bunch of other things in mathematics - I can get behind calling that beautiful.

The special case of x=pi... it's like being excited that sin(pi)=0 or cos(pi)=-1. It doesn't really say anything meaningful or consequential, people like it only because of the symbols it includes. It feels kind of like a math meme that people like to repeat and I can't get behind it.

Maybe it's just not for me and I should just let other people like what they like.

qq4• 5 years ago

I feel this way as well. In fact every time I have tried to remember the "most beautiful equation" I had to think of it in the context of the unit circle and work it out by assigning pi to x. Otherwise I don't get any wow out of it.

CamperBob2• 5 years ago

It doesn't really say anything meaningful or consequential

The impressive aspect of that version of the equation is simply the idea that you can obtain a plain old integer (-1) using nothing but simple arithmetic operations on two random-looking transcendentals.

jstx14• 5 years ago

I really don't like this way of thinking about it.

e isn't important, the exponential function is. e shows up so often because we've chosen to write exp(x) as e^x. It's a result of a notational choice - the fact that exp(1) = 2.718.. and we call that e is pretty insignificant and boring.

Denvercoder9• 5 years ago

The fact that e = 2.718... is a fundamental property of the exponential function, though. It's not an arbitrary choice.

ianai5• 5 years ago

Indeed. That a member of the real number line has this important relationship to the differential operator, the complex plane and number systems, and thus all of trig, calculus, and quantum mechanics is pretty impressive to put it lightly. (Trig through the many relationships of e^x with cosine and sine functions.)

The GP comment reads as either a grab at elite character at best or flat out anti-intellectual at worst. No need to bring it in here.

naasking• 5 years ago

the fact that exp(1) = 2.718.. and we call that e is pretty insignificant and boring.

The constant itself is still pretty interesting. Using e as a base for all numbers yields optimal information density IIRC. Binary (base 2) is close to e so it's information density is not bad, but this also tells us that trinary (base 3) would be even better on this metric since it's closer.

There are lots of interesting properties like this that end up linked to e.

Qem2• 5 years ago

hinkley3• 5 years ago

I wonder sometimes if when Dennard scaling finally grinds to a halt, some desperate and clever individuals will switch us to trinary circuitry, for that last 37% theoretical limit.

neantherpi• 5 years ago

Sincerely, you completely changed the way I look at e. Interesting that ln(x) does follow such a notational style; to change the base one can either divide by ln(b) or use a separate notation (log vs ln). I also had put a lot of weight into e being transcendental but it seems like as long as x is rational the value will also be transcendental, so not that special (if someone could confirm).

mensetmanusman• 5 years ago

I remember the ‘aha’ moment I had in my first year of calculus during a test none the less: “Ohhhh when something is growing in proportion to its current size you set up your derivative equality and get an e^x!” The example used was bunnies with unlimited food; then foxes were introduced.

Was surprised to have that learning moment in the middle of the exam and not prior…

annexrichmond• 5 years ago

sounds like a well thought out exam question. I always appreciated exams where you actually learn while doing it, instead of being in a mode of regurgitation

ianai5• 5 years ago

Oddly it was my calculus 1 final that clicked a lot of things for me. Turned out the authors of the test included a professor who could explain calculus much better than my lecturer for that semester. I remember feeling the most intense and lasting feeling of revelation for several days after that test.

thomasahle• 5 years ago

Was surprised to have that learning moment in the middle of the exam and not prior…

I sat my first exam for a university course I was teaching last year. I thought I needed to introduce some new ideas, so the students wouldn't be bored doing it. From the evaluations, not all students agreed...

nerdponx• 5 years ago

"Bored" is the absolute last thing on anyone's minds during an exam!

I always hated when my instructors put "important" results that we have never seen before on an exam. It was like adding insult to injury if I didn't know how to solve it.

It was different on homework assignments, because usually that you had time to work through the problem in detail and have the "aha" moment, without stress and time pressure.

coupdejarnac• 5 years ago

This is why I have nightmares about undergrad engineering. Professors and TAs lose perspective when they teach the same material repeatedly and think they need to make things interesting. No, your job is to communicate abstract ideas clearly, which is apparently an extremely rare skill.

dtgriscom• 5 years ago

Was surprised to have that learning moment in the middle of the exam and not prior…

Better than at the end of the exam...

analog31• 5 years ago

The foxes bring with them e^(i*x)

quantum_state• 5 years ago

That's why it is physicists' best friend :-).

agumonkey• 5 years ago

Isn't there another fix point like value for hyperoperations ?

jhncls• 5 years ago

In a unique Numberphile video featuring Grant Sanderson (3blue1brown), this weird number pops up in a game of darts.

[0] https://youtu.be/6_yU9eJ0NxA

woopwoop• 5 years ago

This is the most beautiful formula in mathematics, because it includes all the most important constants e, i, pi, 0, and 1:

(ei)^0 = 1^pi

mdp2021• 5 years ago

Unfortunately, it is trivial... A joke. The constants there could amount to almost anything.

westcort• 5 years ago

The reciprocal of e is about 37% and it pops up in a lot of places. Say, for example, you play a lottery 1000 times and there is a 1 in 1000 chance of winning each time you play. The chances you do not win even once is 37%, or 1/e.

hinkley3• 5 years ago

The Secretary problem (#2 in the article) is still one of my favorites.

Stop playing once you’ve seen at least n/e of the available options and the current one is acceptable.

Euler’s number pops up in situations that involve optimality

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