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16:00
Are addition, multiplication, subtraction and inversion allowed in "elementary" operations? Radicals? Exponential and logarithms?
hi
I'd like to know if my question fits math.SE
@BalarkaSen Yes, throw in some trig and friends.
@Alizter OK, trig. But that's just (complex) exponential and logarithms, aren't they?
Sure, good point.
@Alizter It's still open.
16:09
@BalarkaSen Heya
@BalarkaSen An open problem or unsolvable?
Help with me with some notation ?
@Alizter It's open. It can be deduced that from Schanuel's conjecture though, but that is open too, unfortunately.
Hi @N3buchadnezzar.
@N3buchadnezzar Sure.
Hi
Is there a Geometric explanation for implicit differentiation?
I want to split the sum $\sum_{k=1}^n$ into the cases $k=4m$, $k=4m+1$, $k=4m+2$ and $k=4m+3$
16:11
I have objects with spherical coordinates in a horizontal coordinate system and a display which I'd like to show the object's positions on.

Is asking about how I could do that coordinate transformation suitable for math SE or should I ask at some other site like gamedev, scicomp or even a different one?
@N3buchadnezzar Yes?
What is the best notation for it ?
@Christoph We can help you here if you like
by "here" you mean in chat or on math SE?
@Alizter Hey, any answer for my question?
16:13
@N3buchadnezzar Take the case $k = 3 + 4m$. Then write $\sum_{k = 3 \pmod 4, k \leq n}$
@robjohn Is there a Geometric explanation for implicit differentiation?
@N3buchadnezzar I know.
=P
@Christoph In chat
@BalarkaSen also $\pmod{4}$
$k \equiv 3 \bmod 4$
16:16
Yeah, $\text{bmod} $ in nicer.
But $\equiv$ is ugly.
@BalarkaSen You could be lazy and just use "="
@Alizter It's not about being lazy. "=" is more nice and actually not improper.
It's field equivalence.
@Alizter ok, here is what I've got:
I have an object with coordinates on a sphere, in a horizontal coordinate system (altitude and azimuth). I want to display the object's position on a display (x,y canvas) which is centered around a known horizontal coordinate - it displays a certain part of the sphere. The display can be rotated around its normal. How do I find x,y on the display of the object's altitude and azimuth?
@Alizter Also, you can save ink by doing that.
4mm of ink.
16:21
@BalarkaSen $$ \sum_{k=1}^n = \sum_{i=0}^3 \sum\limits_{1 \leq 4m+i\leq n} $$
I do not think that would be double-counting
@N3buchadnezzar Yes, 'cause equivalence classes partition a set into disjoint subsets.
I guess that notation is fine
@BalarkaSen When we integrate over region $R$ (Double integration) , what does $R$ exactly mean?
@MrWho Uh, the region you are integrating over?
@BalarkaSen Yeah, I have bad feeling about understanding notations, I'm asking to be sure.
@BalarkaSen What does exactly $[a,b] \times [c,d]$ mean?
@BalarkaSen Is it Cartesian product here?
16:28
$$
\begin{align}
&\sum_{n=2}^\infty(-1)^n\left(\log(2)-\frac1{n+1}-\frac1{n+2}-\cdots-\frac1{2n}\right)\\
&=\sum_{n=2}^\infty(-1)^n\left(\log(2)-1+\frac12-\frac13+\dots+\frac1{2n}\right)\\
&=\sum_{n=2}^\infty(-1)^n\left(\frac1{2n+1}-\frac1{2n+2}+\frac1{2n+3}-\dots\right)\\
&=\sum_{n=2}^\infty(-1)^n\left(\frac1{(2n+1)(2n+2)}+\frac1{(2n+3)(2n+4)}+\dots\right)\\
&=\sum_{n=1}^\infty\frac1{(4n+1)(4n+2)}\\
&=\frac14\sum_{n=1}^\infty\left(\frac1n-\frac1{n+\frac12}\right)
-\frac14\sum_{n=1}^\infty\left(\frac1n-\frac1{n+\frac14}\right)\\
@MrWho Yes.
Cartesian product of intervals, I'd think.
@BalarkaSen So for instance the answer of this: $[1,2] \times [2,3]$ is ${[1,2],[1,3],[2,2],[2,3]}$ right?
@MrWho No, of course not.
@BalarkaSen So what does it mean? I read that definition of Cartesian product is that.
It's mean the pairs $(x, y)$ in $\Bbb R^2$ with $x \in [1, 2]$ and $y \in [2, 3]$
$[1, 2]$ is an interval, right?
16:32
@robjohn Nice!
@Alizter Applying the display's rotation after projecting the object's coordinate to display coordinates is easy, but I don't know how to do that projection and scaling to the display's resolution
@BalarkaSen Yeah
@Chris'ssis I knew that $\frac1{n+1}+\frac1{n+2}+\dots+\frac1{2n}=1-\frac12+\frac13-\dots-\frac1{2n}$, and that is where I started
@MrWho Then it's just what I said.
@robjohn How old are you? You've got a hand in manipulating series!
16:34
@robjohn I used that in many of my proofs. I also posted it on this site in some answer. :-)
@robjohn Ah, I didn't even recall that.
Nice!
@Christoph Maybe game dev could help you?
@Chris'ssis I use it in an answer where I show how to compute $\gamma$.
@robjohn I think you showed me that in the past.
@MrWho You can always check profiles :-)
16:36
=)
@Chris'ssis How does it follow?
@N3buchadnezzar Use induction. (you're immediately done)
@Alizter probably, but I have a gut feeling that they would first ask about the platform I'm using, which is none.
@Chris'ssis Induction is a bad way to approach it.
@BalarkaSen Sorry??? It's a marvellous approach there!
@Chris'ssis I hate induction.
Try proving it without induction.
Hey @RandomVariable
16:43
Hello @BalarkaSen
@RandomVariable How's your "domination of everything in the world of integral/series manipulation with complex analysis" going?
@BalarkaSen I have to see a proof of mine where I used that ...
wait ...
@BalarkaSen If I sum over $4m$ + $4m + 2$ is this the same as to sum over all even numbers?
@N3buchadnezzar No.
$4 \neq 2 \bmod 4$, even though it's even.
@Chris'ssis Here it is... took me long enough to find it.
16:46
@BalarkaSen At the moment, I'm the one being dominated.
@RandomVariable Really? With elliptic whatnots of Shobhit, I suppose =D
OK, I gotta go.
Hello everyone! Any help here?
@BalarkaSen here ...
thanks!
@BalarkaSen I meant $4m$ and the case $4m + 2$ (as you sure noticed) but point taken
16:50
@BalarkaSen see the induction proof in the first part ...
@robjohn Thanks.
He left now ...
@robjohn I started a thread sort of related to what we've been talking about. math.stackexchange.com/questions/800453/the-function-log1eiz
@robjohn Seriously?55?You're kidding me :)
user116900
47 min ago, some asshole downvoted 2 of my answers.
'Any function $f: U(N) \to \mathbb{C}^{\times}$ can be uniquely expressed as a $\mathbb{C}$-linear combination of Dirichlet characters'.
user116900
It's probably the same idiot who downvoted 3 of my answers the last time.
16:55
@MrWho When I'm 55 I'll consider myself lucky and pretty young.
What do the symbols for the domain and range of this function mean?
@JasperLoy You got lowvoted
user116900
@N3buchadnezzar This user is very nasty, clearly revenge votes.
Feeling blue ?
user116900
Nope, my points don't mean anything, which is why I can delete a 20k account.
16:57
Btw Jasper do you know what my avatar is ?
user116900
No, I don't know.
Click the black square beside my name
user116900
I see the picture.
r9m
r9m
@Chris'ssis for the second limit .. how did you evaluate it ? (I used a mean observation :P )
@r9m I have the solution in some paper I can't find now. I mean it's not me the author of the paper but someone else.
16:59
@RandomVariable Oh hi! waves at you with a complex period
@r9m What observation?
@ParthKohli: you've returned
@N3buchadnezzar Hello
user116900
@robjohn I got 2 downvotes just now at the same time, I will just ignore it, lol.
@JasperLoy Hard to track them down, especially if you don't have any idea who it might be.
r9m
r9m
17:01
@Chris'ssis will you believe me if I said its $\displaystyle \lim_{n \to \infty} \int_0^1\cdots\int_0^1 \dfrac{n}{x_1+\cdots+x_n}\,dx_1 \cdots \,dx_n$ ? :)
user116900
@robjohn I guess I have made many enemies, many people hate me.
@r9m Yeah, sure.
user116900
@robjohn I suspect someone hates you as well.
@JasperLoy why do you say that?
user116900
@robjohn Since you also get mysterious downvotes.
r9m
r9m
17:03
@Chris'ssis :'( ... so u saw thru that too :D .. Awesome !! :D
@r9m I didn's say that. I'm sure you have a proof for that.
r9m
r9m
@Chris'ssis I did it that way :)
@r9m how about my question? $$\sum_{n=1}^{\infty} \sum_{k=1}^{\infty} \frac{\Gamma(k)\Gamma(n^{3/2}+1)}{\Gamma(k+n^{3/2}+1)}\left(\frac{1}{n^{3/2}+1} + \frac{1}{ n^{3/2} +2 } + \cdots + \frac{1}{ n^{3/2} + k } \right) = \zeta(3)$$
@r9m Great then!
@Chris'ssis I imagine the Beta integral plays a part...
I took my exam in complex analysis two days ago. I was asked to compute
$$
\int_0^{2\pi} \frac{\mathrm{d}\theta}{1 + \cos \theta \sin \theta}
$$
^.^ Amongst other things
17:09
@robjohn It depends on the approach.
@robjohn And perhaps $\Gamma(s)\zeta(s)$
@N3buchadnezzar it's twice the integral over half the domain, then change variables.
@robjohn Thats what I did =)
@N3buchadnezzar for what $s$?
r9m
r9m
@Chris'ssis stumped I am .. I am not good with special functions .. I am planning to read about them in this summer ... can you suggest some good reads ? :)
17:11
I meant the integral repsentation of $\Gamma(s)\zeta(s) = \int_0^\infty \frac{x^{s-1}}{e^x-1}\,\mathrm{d}x$
@r9m There are some great books by professor Hari M. Srivastava (the best stuff I've ever read)
r9m
r9m
@Chris'ssis thanks :)
user116900
I think I will just ignore the downvotes, since that user wants to make me unhappy, and try to be happy.
@r9m did you know that $$\sum\limits_{k=2}^{n} {n \choose k} (-1)^k k^{n-1}=n$$?
@r9m (as regards your limit)
r9m
r9m
@Chris'ssis :[D
It's a smiley with my moustache on it ! :P
17:24
;)
user116900
@Chris'ssis Hehe, this is the smiley the person I dislike uses very often, lol.
:-)
brb (I need to visit someone - back later on)
user116900
Although I have an idea who it might be, I cannot email the SE staff to find out as 2 votes is too little @robjohn
@r9m I don't know how good at math I am but I'm pretty good at recognizing a person that knows a lot of stuff: you are one of them. (well, I also like the jokes with the recommended books)
:-)
@JasperLoy definitely, and unless it seems directed at you, and it is not just the person's nature to downvote, it is not an actionable offense.
17:32
Is this reasonable? $\sum^{199}_{k=0}\binom{n}{k}\sqrt{5}^k\equiv\sum^{12}_{k=0}\binom{n}{k}\sqrt{5}‌​^k\mod{(13)}$
I think it may be wrong but I basically got rid of all 13ish things?
@Alizter what is that? I don't think $5$ is a quadratic residue. How are you handling $\sqrt5\pmod{13}$?
r9m
r9m
@Chris'ssis Medical Humor .. wish my bones knew :)
@r9m Did you saw Jack's solution?
r9m
r9m
17:43
@Sawarnik There is a Jack in the box :) !!
@r9m I see :D But now I want to move the bounty!
Grrr...
r9m
r9m
will I put one on his solution ? I was thinking of doing that the moment I read his answer .. he finished along the lines of my initial approach :)
as you want .. not very necessary though :)
@r9m Had you heard of that Japanese Carnot before?
r9m
r9m
@Sawarnik han ji .. :)
@r9m grrr... duniya mein jitna chiz hai sab padh liye ho kya!
user116900
18:17
@Sawarnik Carrot? LOL
user116900
@ಠ_ಠ How is your studying coming along?
@JasperLoy Actually its some theorem, Lol.
@JasperLoy I m very happy.
Someone had to downvote those pesky one-liners you know.
user116900
@ಠ_ಠ Hello Bart.
18:32
Hi @eyes.
user116900
@Sawarnik A one line answer that answers the question is an answer, not a comment.
@JasperLoy Especially when people have left all sorts of comments and answers that describe the situation. You just write one line of that and get rep for free.
None of your answers are worth any points.
user116900
@Sawarnik An answer is an answer, a comment is a comment, end of story. I have been on SE for 3 years.
user116900
@Sawarnik I think I will ignore you.
@JasperLoy That's the lamest excuse I have heard.
18:49
A man, a plan, a canal, PIRAYAS
user116900
@N3buchadnezzar What is that?
Do you not know the palindrome?
Piranhas?
A man, a plan, a canal, panama..
user116900
@PedroTamaroff Hi! What are you studyng now?
18:51
@jasper Now you're just being a turd.
Though Sawarnik is sometimes bothersome.
user116900
@PedroTamaroff Not sure what a turd is, lol.
@PedroTamaroff Oh yeah.
Combinatorics, comm. algebra and rings and modules stuff.
I am thinking about reading Stanley's book when I catch a break.
Probably next semester when I take complex analysis and probability and statistics.
user116900
@PedroTamaroff Never read that. I know it is 2 volumes.
Yes. I'll take it easy though
user116900
18:55
What do you need help with?
user116900
Is my answer correct?
user116900
It seems that he is right and the book is wrong, which is what I said.
You have two cased, each factor is positive or each factor is negative. That is it.
user116900
Erm, I don't understand you. Anyway I think I am correct.
user116900
19:04
The other answerer seems not to understand the asker's method.
howdies mr @Pedro, @Jasper
user116900
@TedShifrin Hi Professor
Hello, wondering if anybody in there is proficient in statistics ... I have a question about the whitening transform.
@Pedro: You gonna teach me probability ahead of when I have to teach it? :)
statistics/signal processing
i'll just ask my question :). i have generated 2 independent uniform random variables, s1 and s2. I then mix them as follows: x1 = a11*s1 + a12*s2; x2 = a21*s1 + a22*s2; I then perform whitening on them to get z1 and z2. I am looking at the distribution of s1, x1, and z1. s1 looks uniform, x1 looks closer to guassian (as expected b/c of Central limit theoreM). z1 looks completely wierd...
i know this is a vague question, but wondering if the problem is the way I am doing whitening? or if i am not calculating the marginal probability of z1 to look at its histogram properly or something?
I do whitening by calculating covariance matrix of x, then doing eigenvalue decomposition in matlab: [E,D] = eig(Rxx); V = E*D*E'; D = diag(diag(D).^-.5); V is my whitening matrix transform.
user116900
19:16
@TedShifrin I am going to bed, see you in my dreams, lol.
night, @Jasper
This is something I know absolutely nothing about, @Kiran.
Bigggg GRRR at that OP!
@Ted
thanks anyway!
Good luck, @Kiran.
@KiranK. It seems that your V is the original Rxx.
19:32
Does anyone have a link to a proof of the divergence theorem that doesn't rely on proving it for 'infinitesimal cubes', then generalising (which I feel is not rigorous)?
@ccorn hmm..., this is the equation I found for whitening in the textbook I am looking at ..., I know that doesn't help you much b/c you may not have the book in front of you
@KiranK. (unless your D is changed prior to the computation of V)
@ccorn, so I computed D as follows: essentially took the squareroot of every element in the D matrix that is output by matlab as a result of the eig call
@KiranK. Your samples are in columns, not in rows?
yes, sorry. s1 and s2 are column vectors, s1 = 1000 x 1, and s2 = 1000 x 1
I can post imgur images of what the histograms are lookign like
if that helps?
19:37
@KiranK. Just test if V*Rxx*V approximates the identity matrix
@ccorn ok testing
and check the size of Rxx
so size(Rxx) = 1000 x 1000.
zzz = V * Rxx * V;
sum(diag(zzz)) = 5.3617e+02 + 1.4991e+00i
that doesnt look good?, i would expect if it was an identity matrix the real part within reason would be lcose to 10000
*sorry 1000
Hello @ccorn
@BalarkaSen Hi Balarka
@KiranK. You want Rxx to be 2x2 I suppose?
19:43
@PedroTamaroff Same here.
Then use row data vectors, not column data vectors.
I am studying commutative rings and algebraic geometry from D&F
@ccorn, oh man, doh
yeah it doesnt make sense for Rxx to be 1000x1000 i guess right? If there are 2 "features", then the covariance matrix should be looking at the dependence between the features, which means it should be 2 x 2?
@KiranK. That's how I understand it. The 1000 are a quite arbitrary number of samples.
@ccorn yes, that makes sense, I will redo it and report back results. Thanks for the help!
19:46
@KiranK. OK :-)
Exactly, @Alizter
I couldn't resist :)
I was wondering why it seemed familiar.
@Charlie
19:48
Just to compare them,
yesterday, by Balarka Sen
user image
Wow, isn't that some coincidence.
@Alizter Masterpiece!
@BalarkaSen How are you
@ccorn just redid it w/ rowvectors, i now get what I am expecting!
What does this symbol mean =: ?
notice the :
19:59
@Sabಠ_ಠ $:=$ means "is defined as"
@KiranK. Wonderful.
Thanks @Alizter :)
@ccorn thank you again!
@Sabಠ_ಠ expr =: name is used to give a name to (the value of) some expression
The name is always where the : is
AHa!
so xdot = 2 + 3x + 4x^3 =: f(x)
This means that f(x) = xdot?
20:03
@Sabಠ_ಠ This means f(x) = 2 + 3x + 4x^3. (In maxima, you would indeed use := for that)
okay
f(x) equals the value
20:14
@Sabಠ_ಠ In LaTeX, $\underbrace{2+3x+4x^3}_{f(x)}$ looks nicer.
@Alizter Fine.
@BalarkaSen What have you been up to recently?
@Alizter Lots of things. Mainly related to the quintic (although vastly scattering up high)
Have you found anything of interest?
@Alizter Sure. Loads. Theory of equation give rise to many interesting stuffs.
It's always sprouting stuffs if you look at it from different perspectives.
Serge Lang once questioned mathematic's knowledge about polynomials. It's very much true : we don't even know the nature of the zeros of polynomials so far, let alone polynomials.
20:22
so are you looking at methods for solving or looking at different properties or both?
@Alizter Well, actually, I am looking at a single method for solving - not general polynomials - but quintics (from different perspectives)
Ah anything interesting recently then?
Yes. Solving a quintic is essentially equivalent to realizing the isomorphism $A_5 \cong \text{PSL}_2(\Bbb F_5)$
In a more simpler language, this is equivalent to the fact that icosahedron is dual to a dodecahedron.
What is $A_5$?
@Alizter Alternating group of order $60$.
20:28
$\text{PSL}_2$?
and $F_5$?
@Alizter Uh, that's a bit complicated. You can think of that as the symmetry group of dodecahedron, though.
@Alizter $\Bbb F_5$ is the finite field of order $5$.
So how would you solve a quintic knowing this?
Or are you still researching
No, solving a quintic is well-known.
I know that. Don't worry.
It is that the symmetry group of iscosahedron acts on 5 objects.
20:30
@Alizter Some number is missing there.
Where the $\text{PSL}_2(\Bbb F_5)$ acts over 6 objects.
So you have a resolvent sextic for a general quintic.
I am at the moment trying to understand what actually the resolvent sextic is. It is supposed to be solvable by elliptic functions.
Hey @PedroTamaroff
@BalarkaSen HAI.
@PedroTamaroff Wonderful things are coming out of quintic stuffs, you know that. It gives out theory of galois covers, modular functions, and probably it may even have something to do with Monstrous Moonshine. I realize I have to learn so much stuff to even understand these things.
I wonder a simple question: is it possible that the serial downvoter to be from this room?
@Chris'ssis I admit it it's me. Ill get you meddling kids!
not really
20:36
@Chris'ssis You never know. Downvoting is anonymous.
I'd like that anyone wants to downvote me to do it in the real life. :-)
(I accept any challenge in the real life in terms of math - the downvoter should know this!)
@Chris'ssis Yes, I'd doubt if anyone can beat you in integrals.
But why do you think that downvoter is from this room?
Serial downvotes are indicative of personal dislike, which is only possible to garner with personal contact, I posit.
@BalarkaSen I only wanted to cover this possibility.
@BalarkaSen I hate no person neither in the real life, nor on the internet. I'm here only for love to math (I mean I cannot think in these terms).
Ah, that makes sense @Alyosha
@Chris'ssis But, perhaps, someone hates you, thus the downvote.
20:41
@BalarkaSen Yeah, perhaps.
But, look at the good side : You can afford downvotes =D
@BalarkaSen :-)
I upvoted your anwers to revert the downvotes @Chris'ssis
i have a question
@BalarkaSen Thank you.
20:45
do we have the ideas of formal systems, formal theories, models in constructive mathematics ? Or is it inherent only to classical mathematics ? For example, Do all meta-theorems of mathematical logic, ( godel theorems, lowenhein-skolem, compactness,etc ) work both for classical mathematics as well for constructive mathematics ?
how is it that h(x) = g(x) - f(x); then h'(x) = g'(x) - f'(x) >= 0? Where did the >= 0 come from?
why is that ssumed?
*assumed
is it possible to notice the main differences of constructive mathematics and classical mathematics ( in all aspects ) in recite them concisely ( but roughly, not precisely ) in a list ? Or would it be a bit too foolish, given that constructive mathematics has many different sub-branches ?
For example, in classical math , suppose we have some bunch of connected mathematical ideas, with time this forms a branch of math and we notice the hierarchy of those connected mathematical ideas and try to capture the essential ones in the axioms, which could allow us to derive many other not-so-trivial related ideas .. in classical math the method of derivation is usely by the arguments that the rules of inference of first-order logic use ...
now would cosntructive mathematics method of formalization be the same except by the allowed methods of derivation ( the kinds of proofs ) ?
@Chris'ssis Giving upvotes for upvotes is a bad practice.
@BalarkaSen What do you mean? No idea.
Especially when the answer upvoted is bad.
@Chris'ssis OK, I just had the impression it was you who upvoted my bad answers.
20:47
@BalarkaSen No ...
That's fine.
why is it that h'(x) = g'(x) - f'(x) >= 0? Why can't it be negative?
my textbook simply says "by assumption"
@BalarkaSen Have you seen these people?
@Alizter Sure.
They may be in competition with @Chris'ssis ;)
20:50
@BalarkaSen You know, I have to tell you something: sometimes I learned precious things from not-too good answers. Moreover, I cannot simply say "this answer is good" and "this one is bad". Even from the others' mistakes I created very nice things.
I have some posts up there.
what if h(x) = x^2 - x^3? Then h'(x) = 2x - 3x^2 which would not be greater than 0?
Mistakes are sometimes terribly precious.
Yes, @Alizter. Well said.
@Chris'ssis Sometimes, yes.
@BalarkaSen All answers are precious (to me)!
20:52
That was a cheek, sorry.
I wondered how Cleo did what he/she did.
@BalarkaSen ;)
@Chris'ssis Any integrals?
@Alizter A double series $$\sum_{n=1}^{\infty} \sum_{k=1}^{\infty} \frac{\Gamma(k)\Gamma(n^{3/2}+1)}{\Gamma(k+n^{3/2}+1)}\left(\frac{1}{n^{3/2}+1} + \frac{1}{ n^{3/2} +2 } + \cdots + \frac{1}{ n^{3/2} + k } \right) = \zeta(3)$$
I wanted someone to talk about constructive mathematics ;( i know nothing about it
20:56
@Chris'ssis I tampered with that a bit yesterday ill have another go
@Chris'ssis Aahh! That's a generalization to what I saw!
@BalarkaSen Indeed! :D
http://math.stackexchange.com/questions/800788/please-help-asap

That's funny.
PLEASE HELP
@G.T.R I was about to ask what you needed help with then I saw the above link.
21:09
@G.T.R THE FIRST STEP IS TO ADMIT YOU HAVE A PROBLEM.
Anybody looking forward to that Watchdogs game?
@G.T.R Don't know what those are, Guitar.
Any Eurologue Baskteball fans?
@Pedro get out of your cave, it's the next Ubisoft game
@Student Euroleague?
That's right @G.T.R
21:17
@PedroTamaroff Do you know how were the simplicity of PSL groups demonstrated?
@Student unfortunately no, everytime basket is on the mainstream news, it's about NBA or some international competition
Shame..
@Student is there a team you support?
An Israeli team just won the finals :)
@Studentmath My math advisor just got back from Israel.
21:20
How has it been for him?
@Studentmath We haven't talked face-to-face, as he is in TIFR right now, but he says that it's been real cool there. 26 degrees! Who'd have known!
We've had worse
And we are fried to death here in WB (42 degrees).
@Studentmath Ah? How much?
In the south? I'd say about 40s
Cool.
I mean hot, sorry.
21:28
:P
This one is cute (newly created for some students) $$\sum\limits_{k=2}^{2014} (-1)^k{2014 \choose k} k^{2013}$$
(well, it's also for fun)
@Chris'ssis Did you do it combinaotirally?
@BalarkaSen It can be done in more ways I think.
In general, if you replace $2014$ by $n$, it's possible to get combinatorial interpretations.
@Balarka Galois proved their simplicity.
21:40
@PedroTamaroff That's fine, but I asked if you can give me the general idea of the proof.
I have no idea.
Try looking in Rotman.
A way of writing $5$ ... let's see it
5=1/(-Sqrt[5] PolyGamma[0,1+5 Sqrt[5]]-25 Gamma[1+5 Sqrt[5]] (Hypergeometric2F1Regularized^(0,0,1,0))[1,1,2+5 Sqrt[5],1])
22:46
@BalarkaSen I have an exercise for you: let $G$ be an abelian $p$-group. Show that if $G/pG\sim \Bbb Z_p$, then $G$ is cyclic.
22:59
@PedroTamaroff You have rotman?!

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