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9:01 PM
Is it possible to find a closed form answer for this integral? $$ \int_{0}^{1} \dfrac{x^2 - 1}{\log x} \text{ d}x $$
 
@Khallil sure
@Khallil I am going to tease you and say $\log 3$
 
$$\int_{0}^{1} \int_{0}^{1} x^{y+1}+x^y \text{ d}x \text{ d}y$$
 
Stupid question... how do you turn on MathJax on chat again?
 
click on it
 
@Khallil Differentiate $\int_0^1 (x^a-1)/\log x dx$ w.r.t. to $a$, profit.
 
9:10 PM
Click on what?
 
the link
 
Oh, I see. Thanks!
 
np
 
Test $x + 2$
No luck here. -_-
Oh! I got it now.
:D
 
@PedroTamaroff I did that integral that way. I forget, how do we check C is zero?
 
9:15 PM
Have any of you here done the actuarial exams?
 
What exams ?
 
uni entry
 
@Alizter You mean the integration constant?
 
@PedroTamaroff yes
 
Exam C/4.
 
9:16 PM
You can take the integration constant you like.
 
Oh yea, differentiation under the integral sign. Thanks, @Pedro!
 
Set $\Phi(a)=\int_0^1 \dfrac{x^a-1}{\log x}dx$
 
No idea what C/4 is :c
 
Then $\Phi'(a)=\frac{1}{1+a}$.
 
@PedroTamaroff lack of sleep
I am being an idiot
 
9:17 PM
Construction and Evaluation of Actuarial Models.
 
can't believe what i just asked
 
Now $$\int_0^t \Phi'(a)da=\Phi(t)-\Phi(0)=\Phi(t)$$
 
Huy
9:32 PM
@Alizter: Try sleeping more.
 
@Huy sure
 
Aaaah no
you removed it right before i saw it :c
Aah better :)
Wow
$403/1280$
 
Ah, quelqu'un d'autre qui vient de la France ...
 
Where does that even come from ?
@TedShifrin Uh ?
 
hides from @Balarka
 
9:43 PM
Hello @TedShifrin
 
@BalarkaSen-pai
 
@TheGame You missed to tell me something important there.
 
@TedShifrin You hide well ^^
 
@Khallil Split the integral, use IBP.
 
@Chris'ssis What is it ?
 
9:44 PM
bien sûr, @TheGame
 
@BalarkaSen I have a problem for you.
 
mr @Pedro !
 
@TedShifrin Uh, hello.
 
@TedShifrin HERRO.
 
OK, @Pedro
Bah didn't work. Nevermind.
 
9:45 PM
@BalarkaSen Da hell ?
 
Let $f_n:\Omega \to \Bbb C$ be a sequence of functions. Suppose that $f_n(x_n)$ converges for every $x_n$ convergent in $\Omega$. Prove that $f_n$ converges pointwise to a function $f$ in $\Omega$, and that $f$ is in fact continuous.
 
Analysis. Bah. I was hoping for some algebra.
 
LOL .. Time to broaden yourself, @Balarka.
 
Who starred that?
 
@TheGame $$\Re \bigg(\text{Li}_3 \bigg(\dfrac{1-i}2\bigg)\bigg) = \Re \bigg(\text{Li}_3 \bigg( \dfrac{1 +i}2\bigg)\bigg)=\dfrac{\ln^32}{48}-\dfrac5{192}~\pi^2~\ln2+\dfrac{35}{64}~\zeta‌​(3)$$
 
9:46 PM
You fool.
 
Not quite Arzela-Ascoli, eh, @Pedro?
 
@PedroTamaroff What is le $f$?
 
@TedShifrin Nah. Close, though. Continuous convergence (the above) is equivalence to compact convergence to a continuous function.
 
@Chris'ssis I have no idea where that comes from but ... what's the link ?
 
$f$ is le pointwise limit.
 
9:47 PM
Ah, missed that.
 
7
A: Closed Form for the Imaginary Part of $\text{Li}_3\Big(\frac{1+i}2\Big)$

CleoIf you consider a hypergeometric function to be a closed form, you can have the following result: $$\Im\left[\operatorname{Li}_3\left(\frac{1+i}2\right)\right]=\frac{\pi^3}{128}+\frac\pi{32}\ln^22+\frac14\,{_4F_3}\left(\begin{array}c\tfrac12,\tfrac12,1,1\\\tfrac32,\tfrac32,\tfrac32\end{array}\mid...

 
Someone is going star-crazy.
He should stop.
 
@Chris'ssis Theorem Every solution to a problem posed by Chris is a rational algebraic combination of $\pi^k,\log^k 2,\zeta(k)$
17
 
@Chris'ssis ah Tunk-Fey knows what he is doing!
 
@PedroTamaroff LOL
 
9:49 PM
@PedroTamaroff That's a conjecture.
 
@Chris'ssis I don't get it ...
 
$\gamma$ is not yet known to be a rational combination of those, AFAIK
 
@BalarkaSen I proved it but Chris wrote an integral over it and the proof is lost.
 
You people and your stars.
 
Also, come on. You got work to do-.
 
9:49 PM
That problem?
Oh boy.
 
@TheGame don't worry about that part with understanding ... Try to get used with things.
 
@Chris'ssis Cleo gave the im part. You showed me the Re part. What is the link with the post you have now deleted ?
 
Nah I can't do it @Pedro it's just too hard for me.
 
@BalarkaSen You don't have to solve it right now.
You can sleep on it.
 
There are two star-crazy users in this chat
 
9:52 PM
I think I've only ever starred something once, and that was upon request.
 
By Jasper? LOL
 
>_> As long as it's not the holy video :D
 
no, to get the LaTeX in chat back in the star list.
 
@hippa change you name back
it suited you
 
@BalarkaSen Let's try to confirm it.
Jasper is awesome.
 
9:53 PM
@Alizter I can't
 
I'm totally serious about the above.
 
Jasper is halarious
 
@Alizter There is a delay of some days between two usernames change
@Alizter What is more, I'm making people lose that way :D
 
@TheGame kinda like getting a tattoo? regret and all?
 
OK, I starred to give a push.
But retracted it.
 
9:53 PM
so you've had a double identity for four months, @TheGame?
 
@Alizter No regret so far I've mane many people lose :D
@TedShifrin That name is brand new -__-
 
@TheGame
 
It says four months.
 
@TedShifrin Tunk-Fey is Cleo
 
Huh? @Alizter
 
9:54 PM
Let's call Hippa @The
 
I preferred Hippa.
 
@TedShifrin You know Cleo?
 
Maybe his computer exploded.
 
@TheGame see above
 
9:54 PM
I don't think so, @Alizter.
 
@Chris'ssis Ah meh stoopid
 
Plausible enough @Ted
 
The one that provides no explanations to their answers
etc.
 
@TheGame :D
 
@TedShifrin But now you can lose all you want :D
 
9:55 PM
Lose, @leJeu?
 
@Ted would you shave your tache for charity?
 
The Game is a mental game where the objective is to avoid thinking about The Game itself. Thinking about The Game constitutes a loss, which must be announced each time it occurs. It is impossible to win most versions of The Game. Depending on the variation of The Game, the whole world, or all those aware of the game, are playing it all the time. A number of tactics have been developed to increase the number of people aware of The Game and thereby increase the number of losses. The origins of The Game are unknown; a game featuring ironic processing was played by Leo Tolstoy in 1840. The Game has...
 
I dunno, @Alizter ... It's been 40 years.
 
LOL @TheGame
 
@TedShifrin I would pay...
 
9:56 PM
I'll be even uglier without it :D
 
@TedShifrin You can drink maple syrup out of a cup no mess.
 
LOL, yeah, I do that every day.
 
@TedShifrin I heard that over time, taches consume a persons philtrum leaving but a plain lip.
@TedShifrin prove this
 
I have no idea what you're babbling about, @Alizter.
 
9:59 PM
@TedShifrin Now you know what your undergrads feel like.
 
some of them, sometimes, yes ... but I already knew that
 
skips away whistling
 
see if I ever help you again, @Alizter
 
@TedShifrin Can you help me?
ahh im not being serious
sorry ted
 
@TedShifrin Is Luroth true for, say, $k(x, y, z)$?
 
10:02 PM
dunno @Balarka ... I don't even remember Lüroth, although I once knew
 
There is no intermediate field between $k(x)$ and $k$ -- that one.
 
woo new southpark today
 
@PedroTamaroff ask your professors to compute this limit
15
Q: Computing $\lim\limits_{n\to\infty} \Big(\sum\limits_{i = 1}^n \sum\limits_{j = 1}^n \frac1{i^2+j^2}-\frac{\pi}{2} \log(n)\Big)$.

Chris's sisIn the chatroom we discussed about the asymptotic of $\displaystyle \sum_{i = 1}^n \sum_{j = 1}^n \frac1{i^2+j^2}$, and if we think of the inverse tangent integral, it's easy to see that $\displaystyle \sum_{i = 1}^n \sum_{j = 1}^n \frac1{i^2+j^2}\approx \operatorname{Ti}_2(n)\approx \frac{\pi}{2...

 
@Chris'ssis Most of my professors aren't into that.
 
@PedroTamaroff most?
 
10:04 PM
@Alizter OK, you got me. None of my professors are into that.
 
yes, well, computing limits and series and integrals are not quite popular mathematics
 
I have to figure out an example in the Probability book. It's real-world practical, and it makes no sense to me. How many items a store should purchase versus how much they have in stock to sell ... Agh.
 
@BalarkaSen Do you even read yourself? :-)
 
@PedroTamaroff @BalarkaSen leave them alone
 
@Balarka @Ted
\o
 
10:05 PM
@Pedro: To be correct, it should be "none of my professor is into that." :D
 
@Chris'ssis erm, read what?
 
((@studentmath))
 
@Studentmath!
 
@BalarkaSen The things you write ... are not quite popular mathematics? Who established that? ;)
 
my probability exam is tomorrow, so I can send it tomorrow if you're really interested :D
 
10:06 PM
@TedShifrin Really?
Tilts head.
 
yup @Pedro
 
@Chris'ssis er, I don't get you sorry.
 
none = singular
 
Prof. @Ted that'll be great :)
 
Since I can't teach you math, @Pedro, I might as well teach you English syntax :D
 
10:06 PM
@Chris'ssis dunno, i just never heard of it being a great well-known branch of mathematics.
 
@Studentmath, send me an email ... I'm sure I'll never find it again.
 
@TedShifrin Where are you going for retirement?
 
@Ted is it from teh book I studied with?
 
@TedShifrin I was reading your multivariable analysis book yesterday. I really want to learn about manifolds. =)
 
yes, @Studentmath
 
10:07 PM
@Ted Which page? (maybe the translation to hebrew clarified few things)
 
nvm i'll drop the discussion to save myself from being rammed up ducks aways
 
You should start with Guillemin and Pollack, @Pedro ...
 
@BalarkaSen Maybe because you weren't ever interested in it.
 
Unless you really want abstract manifolds (not embedded in $\Bbb R^n$), in which case you can look at Jasper's bible, Lee's Differentiable Manifolds, or any number of other texts.
 
@TedShifrin i can't even compute multivariable limits
 
10:08 PM
@TedShifrin Is that the canonical reference?
 
wait i though abstract manifolds don't exist?
i.e., all abstract manifolds are smooth
 
That's what my students are turning in tomorrow, @Balarka. In the obvious cases, there's nothing much to worry about. But there are pathological cases where limits don't exist.
which @Pedro
Guillemin and Pollack is beautiful, and teaches you about intersection numbers and transversality, with all sorts of fantastic deep theorems.
 
@TedShifrin Nice. =)
 
no, @Balarka ... Plenty of non-smooth manifolds.
 
@TedShifrin I never groked the methods. I can't imagine surfaces.
 
10:10 PM
I might as well finish Spivak's manual, too. I am only missing the last chapter!
 
Well, given how algebraic you've become, @Pedro, you might as well learn about singular chains, etc.
If you're interested, @Pedro, a few of the videos from last spring have some nontrivial integrals of differential forms over tori in $4$-space, etc., application of Stokes's ...
 
@Pedro is dangling between algebra and analysis, @TedShifrin
 
@TedShifrin Sure, yes.
@BalarkaSen Love both.
 
@ccorn Hello again
@PedroTamaroff i realized analysis is too hard for me =(
 
Well, since I'll be in a hovel somewhere when @Pedro becomes a grad student, I have no more vested interest :P
@Balarka: You haven't even tried.
 
10:12 PM
@BalarkaSen You haven't studied any analysis!
 
no, i did
it's hard
 
Michael Artin told me years ago that he went into algebraic geometry because it was the hardest for him.
 
I like algebraic geometry!
Very algebraic.
 
@BalarkaSen Hi again
 
the algebraic geometry I learned/did for research was less algebraic ...
but you really don't know much at all, @Balarka, so chill.
 
10:13 PM
Well, I am reading from D-F so it's a bit algebraic I guess
 
@BalarkaSen To me, there is only one problem as regards the mathematics I do, not the one you mentioned, but the fact that these things become easier and easier, and this scares me to a certain extent. The limit I posted yesterday was so welcome, the one created by robjohn.
 
nothing close to algebraic geometry ... the Nullstellensatz is foundational, as is localization.
 
I like it anyhow. The interaction with comm. alg are cool.
@TedShifrin Well, fun anyhow, whatever the name may be
 
it's algebra, @Balarka.
 
i don't care about names
 
10:14 PM
Don't start that crap.
 
@TedShifrin huh, well, that explains it
 
So.. Rudin's analysis so far proves really interesting. Hope I have enough time to read through it all next couple of months.
 
what are some good books on blackjack theory?
 
Reading is not the point, @Studentmath. Do most of the exercises.
 
Or well, find time..
@Ted yeah, that's what I mean with reading through it all.
 
10:16 PM
IF you want to do graduate work in math, @Studentmath, being able to do most of Rudin is a good start :P
 
@Ted as you (I think it was you) said once, math is not spectator sport :P
 
Yes
 
Yup, I've said that, @Studentmath :P
 
The exercises are that tough?
 
Many of them are, yes.
I still detest Rudin's style ... not a single picture in any of his books.
 
10:18 PM
I have decided though @TedShifrin that I'll thoroughly study first the topics D-F contains, then think about analysis.
Is that good?
 
Thanks, @Balarka!
Hey, @Ted!
 
It's weird to be at graduate level in one part of math and know nothing about the other parts, @Balarka.
 
@TedShifrin That's what Arnol'd said.
 
hi @Khallil
I told you I liked Arnol'd.
 
@TedShifrin Wait I though D-F is only an undergrad survey!
 
10:19 PM
Are there any pictures in Sheldon's book? I don't recall any..
 
i would just do real analysis by fitzpatrick and royden. Even an undergrad can read it as well.
 
No, it's graduate level. Not for Princeton (which assumes everyone knows first-year graduate math)
 
The only book with pictures I recall was in graph theory..
 
LOL ... @Studentmath: In my algebra book, I have zillions of pictures.
 
Why can you choose any constant of integration when differentiating under the integral sign, @Pedro?
 
10:19 PM
Pictures in Algebra?!
 
Huh? @Khallil
 
The most pictorial book I read was Arnol'd's lectures on geometric galois theory.
 
yes, @Studentmath!!!
 
The projections of the subjects into geometry?
 
pictures for cosets, quotient groups/rings, and plenty more.
 
10:20 PM
@TedShifrin What does your book cover?
 
@Khallil Do you know how to integrate $$\int_0^1 x^y \ dy$$? If yes, use the double integrals, change the order of integration and done.
 
my book is definitely undergrad, @Balarka ... not for anyone here.
 
Not even for moi?
 
It is a rings-first treatment of all the standard stuff, culminating in Galois theory. But I have a last chapter on affine and projective geometry. That makes it unique.
 
@TedShifrin What about the exercises?
 
10:22 PM
Some of them are pretty good, but it's way too elementary for you.
 
Can't you use the fact that the exponential and natural logarithmic functions are inverses, @Chris'ssis?
 
Mhm, OK, @TedShifrin =(
It's just that D-F's theory is pretty bad.
 
Huh?
 
In the US, do undergraduates have to write some sort of seminar paper in their last year, covering some advanced topic? Not really research, but dealing with research papers and so on, combinig them and adding personal comments and so on?
 
no, @Studentmath
at a few liberal arts (small) colleges, perhaps
 
10:23 PM
I don't like D-F's approach on the write-up of the theories, @TedShifrin. Artin is way better when it comes to that.
 
I wonder where we took it from then. Maybe Europe
 
@Chris'ssis $$ \int_{0}^{1} x^{y} \text{ d}y = \int_{0}^{1} e^{y\log(x)} \text{ d}y = \dfrac{x^y}{\log x} \Bigg|_{0}^{1} = \dfrac{x-1}{\log x} $$
 
But sadly Artin covers less topics than D-F
 
that's because Artin is a deep mathematician, and wants to show the global interactions, @Balarka.
 
@Khallil $$\int x^y \ dy= \frac{x^{y}}{\log(x)}$$
 
10:23 PM
Artin wrote specifically for (talented, i.e., MIT) undergraduates
 
Yea, I just worked that out, @Chris'ssis. ^_^
Look above!
 
Oh, OK.
Well, I'll have to go with D-F then.
I have to go. Byes @Ted
 
You could read Lang instead, @Balarka.
 
@Khallil Now, you can arrange your staff there and you're done ...
 
@TedShifrin makes sniffing noises that's... pretty old!
 
10:25 PM
often old is better ... not sure in this case
 
I managed to finish it off, but I couldn't understand the reasoning behind choosing an arbitrary constant of integration (like 0), @Chris'ssis.
 
reading some of the early 20th century classics is often illuminating
OK, I need to go cook dinner.
 
\O_o/ Who knows. We'll, I guess I'll try it out
I have to go too.
See you @TedShifrin
 
bubye
 
This is what I'm talking about, @Ted.
 
10:27 PM
@Khallil Well, when playing with the differentiation under the integral sign you need to wisely choose a certain value for the additional parameter such that you can cleverly extract the constant.
 
Oh, ok. Is there any particular reason why that certain extraction applies to the general integral we're working with (like $I(a)$), @Chris'ssis?
 
@Khallil you have $$I(a)=\int_0^1 \frac{x^a-1}{\log(x)} \ dx=\log(a+1)+C$$
 
I'm already aware that $I(0) = 0 \implies \mathcal{C} = 0$ so I don't need help with that.
Just with the reason why the constant for a single case like $I(0)$ can be extended to $I(a)$.
Ahh, I'm too late. Enjoy the dinner, @Ted!
 
@Khallil because the constant remains the same for all $a$ as you define it
 
I just noticed that I've been doing the same thing whilst solving differential equations at boundary conditions.
Hmm.
 
10:41 PM
You have more examples there.
 
Thank you, @Chris'ssis. ^_^
 
10:57 PM
@Khallil no C it is definite
 
$$ I'(a) = \dfrac{1}{a+1} \implies I(a) = \int \dfrac{1}{a+1} \text{ d}a = \log | a+1 | + \mathcal{C} $$
 
11:26 PM
@robjohn
Suppose I have marked in the real line a number $0<r<1$. Using a straight edge and compass, how can I mark the number $r^{-1}$?
 
11:39 PM
@Pedro: You need to use similar triangles. With compass and straightedge you can draw parallel lines, copy angles, etc. also, remember that you have a distance of $1$ to work with.
 
@TedShifrin I have no idea what to do.
 
Make a triangle with sides $1$ and $r$. Then copy distance $1$ on the line with length $r$ already marked.
 
@TedShifrin The "r" side should lie on the x axis?
 
Ok, sure.
 
OK, now I have made that.
What now? =P
 
11:44 PM
Put $1$ on the y-axis. (You can draw a perpendicular line through a constructed point.)
 
Night all!
^_^
 
Night, @Khallil
 
@TedShifrin And? =D
 
Do what I said above ...
 
11:51 PM
@PedroTamaroff draw a $1$ unit line perpendicular to the real line at the point $x$. Draw a circle centered on the real line containing $0$ and the upper end of the perpendicular line. The other point at which the circle intersects the real line will be at $\frac1x$
 
I already did that.
 
Hush, @robjohn :)
 
@TedShifrin I just saw Pedro's question... was this a quiz for him?
 
@robjohn OK. How does that work, though?
@robjohn No, no.
I was curious.
 
Well, as @robjohn told you, you should have $1/r$, then :)
For smart guys like @Pedro I don't give answers away :D
 
11:54 PM
@PedroTamaroff Draw a triangle inscribed in the circle which has the diameter as one side.
@PedroTamaroff then you should be able to see some similar triangles and figure out how it works.
 
@robjohn Oh, the circle should pass through those two points. OK.
 
<--- no longer needed :)
 
How do I make the circle pass through those two points exactly though?
Oh.
 
Today was bunny rescue day for me...
 
Perpendicular bisector, right?
@TedShifrin Silly.
 
11:56 PM
@PedroTamaroff yep (where it intersects the real axis)
 
DANG. I don't have a compass.
 
@PedroTamaroff not even a moral one?
 
LOL ... Use pencil and string :)
 
@robjohn What's that?
 
Good one, @robjohn, bunny rescuer :)
 
11:59 PM
OK. I have string.
 

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