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00:08
@SimplyBeautifulArt define 'analytic'?
im curious now
@TheGreatDuck A function is analytic on an open set if it is equal to its Taylor series on that set.
@Fargle well, i was thinking that a fractal that anyone could produce would be fairly intriguing.
:p
@TheGreatDuck $\forall c\in D\exists r>0(f(x)=\sum_{n=0}^\infty\frac{f^{(n)}(c)}{n!}(x-c)^n\forall0<|x-c|<r\implies f\in C^\omega\forall0<|x-c|<r)$
where $D$ is the domain of $f$.
@TheGreatDuck I guess you could use the Koch snowflake as a motivating example for there being functions which are everywhere continuous and nowhere differentiable.
@Fargle "equal to its taylor series on that set"
00:10
Hm, did I do that right?
not sure
@SimplyBeautifulArt It actually has to be true for any point $c$ in $D$.
taylor series is not my strong suit
what counts as analytic?
00:12
Things like $e^x$ and $\sin(x)$, all of which satisfy the above.
what about x^2?
@TheGreatDuck Sure. Its power series is itself.
continuous functions?
Any polynomial is equal to its own Taylor series.
00:14
@TheGreatDuck Stronger than continuous functions
@TheGreatDuck Not all continuous functions--the Weierstrass function is a good example. It's everywhere continuous but nowhere differentiable, so you can't make a Taylor series at any point.
i meant are continuous functions analytic
ah
My point being, a continuous function can be nowhere analytic.
but all smooth functions are
Infinitely differentiables need not be analytic either
So no
00:14
oh
Right, I think $e^{-x^2}$ or something close is an example?
Well, not quite, $e^{-1/x}$.
so they are a subset of smooth functions?
There's also $e^{-1/x^2}$
I'd rather use
$$f(x)=\begin{cases}e^{-1/x^2},&x\ne0\\0,&x=0\end{cases}$$
which is smooth but not analytic
That's what I meant, yeah.
00:15
@TheGreatDuck yup
@SimplyBeautifulArt what are they useful for?
So, if an analytic function has a Taylor series of 0 at some point
Approximations, complex analysis, lots of stuff man
00:16
@TheGreatDuck If you have a Taylor series representation for a function, it's really really easy to approximate values for the function itself.
Then it is identically 0, everywhere
For example.
However, those smooth non-analytic functions allow you to get a compactly supported function which is non-zero
Oh did you just mean Taylor series?
i meant what is the purpose of analytic functions in a nutshell.
Approximating functions
00:17
like, they're primary usage in solving problems.
ah
@TheGreatDuck e.g. If you needed a rough answer to sin(0.1), you could consider $T(0.1) = 0.1 - \frac{0.1^3}{3!} + \frac{0.1^5}{5!} - \cdots$
so are analytic functions the set of all possible taylor series?
@Fargle ok. I see.
@TheGreatDuck They are the set of all functions representable as their Taylor series
An analytic function is a function that is locally given by a convergent power series
@SimplyBeautifulArt but are there functions which give out taylor series that are not analytic functions?
00:19
@TheGreatDuck Of course. You can take the Taylor series of any smooth function in general
Analytic functions are the ones that actually equal their Taylor series
Simple example
@SimplyBeautifulArt im not asking if 'f' is analytic. I'm asking if T(f) is analytic. Are the resulting taylor series ever not analytic?
How can a Taylor series not be analytic?
@TheGreatDuck A Taylor series is analytic
@TheGreatDuck Taylor series considered as functions in their own right are always analytic on their interval of convergence.
Surely it equals itself...
00:21
An analytic function is one which is equal locally to its Taylor series
So a Taylor series equals itself
oh ok
i didn't know whether taking the taylor series of a taylor series gives back itself
derivative rarely does that
The Taylor expansion of a Taylor series is itself
ah ok
:p
so does that mean $analytic \equiv taylorSeries$
@TheGreatDuck Well, what would T(c), T'(c), and so on, be, working from the definition of the Taylor series of a function at c?
@Fargle i don't know and I was referring to the derivative in general.
00:23
@TheGreatDuck Well, the derivative of a Taylor series is still a Taylor series, so the derivative of any analytic function is analytic
What I'm getting at is that the Taylor series at c is constructed in exactly the way that makes it the nicest to take derivatives of at c.
so analytic functions are infinitely differentiable?
@TheGreatDuck Yep. Every analytic function must be smooth. If not, then there is some final derivative that makes sense, and the Taylor series can't be constructed past that degree.
@TheGreatDuck This gets weirder for complex functions: a function $f: \Bbb C \rightarrow \Bbb C$ is analytic if and only if it is differentiable (only once!) on an open set.
Differentiability really means different things in C than R
Agreed, @Balarka.
00:29
Yup
One derivative leads to infinitely differentiable and analytic
It looks the same but to me it's a PDE condition on $f$
@SimplyBeautifulArt Only on an open set, though. At a point isn't enough.
Good grief — is Balarka still un-unsleeping?
hi @Fargle, @Simply
Hello @TedShifrin
00:36
@TedShifrin Howdy! How goes it?
Pretty well, thanks ...
How're you all?
Alright. Been working through some algebra.
Hey there @Ted!
Hi Demonark
Good life choice @Fargle! :P
00:37
Hmm, don't forget multivariable and diff geo :P
@TedShifrin Scratching my head about multi-argument functions in Ruby
@TedShifrin I haven't. I've gotten decently far in your book and lectures.
cool ...
Resp. chapter 3 and chapter 5.
Aha ...
Glad you're being primary.
00:39
What do you mean?
You said algebra, so I said primary ... fancy version of prime.
Ah. Solid pun, I'm sad I missed it.
well, no, if you get far enough in algebra, there's something called primary decomposition in commutative rings generalizing prime factorization in $\Bbb Z$.
But, yeah, you missed it :P
Time to read Atia (or whatever the book Karim was using) then, ready Fargle?
00:41
But I'm about to disappear — going to a party at a friend's house.
Atiyah ... nowhere near ready, Demonark.
@TedShifrin Sounds like fun! Have a good time.
@TedShifrin And yeah, you're probably right about that.
@Daminark More like time to read Artin.
Lol, perhaps
I haven't used Artin much actually, mostly Herstein, Rotman, and a bit of Aluffi
I have too many algebra books.
I don't know which one to use.
00:45
Right?
Artin is sort of unique in integrating linear algebra and tying into all sorts of different things in mathematics (e.g., representation theory, Hopf map, Riemann surfaces).
Fraleigh, Artin, D&F, Hungerford, and Aluffi.
Fargle, I was supposed to send you algebra exercises, but most come from my book. I can, however, send exams as a start for you, if you want. Remind me later.
@TedShifrin I would be much obliged.
I've got Aluffi, Mac Lane, Artin, DF
Rotman for groups
00:47
I just don't know which would suit me best, but I guess the only way to find out is to dive into one of them and, here's the catch, stick with it
Herstein I used to have but it lacked some stuff that was important with Laci like Jordan-Holder
Lol sticking with things has never quite been my specialty
:P
The trouble with finding things easy for a long time is that you don't have a system for when it gets hard.
Bye, guys. Bis später.
Au revoir!
See you @Ted!
00:54
adios!
Hello @heather, long time no see
hello @Fargle
lots of school projects to finish up. next week friday is my last day, so that'll be nice.
Last days are always my favorite days.
01:14
Minus exams
I've always been an avid and skilled test taker.
If only that were applicable.
Lel
I dunno, the way I've started working in college isn't compatible with testing. I tend to do well enough on them anyway
Still isn't my thing
01:29
have you guys heard of the MAP test?
it's a standardized test
and it's kind of cool, because it's on a computer, and it adjusts the questions depending on how well you're doing, so if you get one right, it'll give you a harder one.
there's a reading one, a math one, and a science one, I think.
it's the only good standardized test i've ever taken.
01:42
I've never heard of it.
It sounds good though.
@Waiting yea, whats Astyx said. I'm quite often here, except for today. But hi, always nice to see you.
@BalarkaSen That actor killed it.
I like what he did. That's how I imagined it being said when I read the play.
02:04
It's been a long time since I read it. I need to again.
That monologue is brilliant any way you slice it.
Me too. I always found it rather hard to read in one go though, even if it's supposed to be a minimalist satirical tragicomedy. The setup/environment/repetitive nature of the story somehow gives a terrible sense of claustrophobia.
@Fargle Oh yeah I loved it
Have you read Imagination Dead Imagine by Beckett? It's a 2 page stream of consciousness monologue
somehow quite like Lucky's rant
I should read it.
Hello everyone.
02:20
hi
Hall0
02:52
weird thought: continuous minesweeper
Anyone here know stuff about towers of quadratic field extensions?
hurr hurr hurr
give me a bit
how would you know if you flagged a bomb?
@Excalibur42 I don't, sorry.
@dair no in the sense that bombs take up area and you are given 3D plot showing the area of bomb material around that point
so basically the bombs are contiguous shapes like blobs
in what sense does the game end?

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