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00:23
I can't remember why if $n\ge\aleph_0$, the direct product of $n$-many copies of a field has dimension $>n$.
I guess I didn't know that, @blue.
it's harder to write down a proof than I'd imagined
Oh, Hamel basis ...
00:47
@Mike I proved it, btw.
Why does it always happen with me. Whenever I come people freezes up. This is so not fair.
Can anybody rearrange $x^{x^x}=y$?
@Alizter Rearrange?
for x
Oh you mean expressing $x$ in terms of $y$?
00:57
You'll end up with a lot of Lambert logs I guess.
I get as far to $\displaystyle\large\frac{\log y}{x^{x-1}}e^\frac{\log y}{x^{x-1}}=x\log y$ ready for Lambert but that x on the RHS kills me.
Perhaps it's not expressible in terms of Lambert logs.
I wonder if it is?
c c
c c
@PedroTamaroff with $$f(t,s)=\int_0^{\infty}\frac{x^s}{(1+e^{tx})^2}dx =\int_0^{\infty} -\frac{d}{dt}(\frac{x^{s-1}}{1+e^{tx}}) dx =\int_0^{\infty} -\frac{d}{dt}(\frac{u^{s-1}}{t^s(1+e^{u})}) du $$ $$= -\frac{d}{dt} (\frac 1 {t^s}\Gamma(s)\eta(s))=\frac s {t^{s+1}}\Gamma(s)\eta(s)$$, then we should differentiate in s to find $$\frac{\partial f}{\partial s}(1,0)=\int_0^{\infty}\frac{\log x}{(1+e^x)^2}dx$$
@Alizter I don't think it is. Look at the growth rate of those functions.
It's about the same as saying that $\exp(x)$ can be inverted using fractions.
If $y$ is a given constant, then things change though.
01:02
Sure but $x^{x^{\textstyle.^{\textstyle.^{\textstyle.}}}}=y$ can be written in terms of $x$ and that has a crazy growth rate
@Alizter I am talking about the slowness of the growth.
In any case, i don't know and i am not sure.
you have to precisely define what you mean by 'writing' in terms of something.
i have to go.
c c
c c
Balarka, thanks for the previous explanations
I mix 'sooner' and 'earlier' for some reason
r9m
r9m
01:45
@Pedro HBD =)
02:04
I'm playing a game where you have to construct things with a straight-edge and compass. There are some levels where, once you beat it, you get a tool that lets you do that thing for convenience (e.g. an "angle bisector" tool). The level I'm stuck on asks for the incircle of a triangle. I have a solution that I believe should work, but it's not being accepted. Is there a bug in the game or is my understanding wrong? i.imgur.com/12OAIuW.gif
Aha! I solved it. I assumed that the circle would touch the outer line at the same point the angle bisector crossed it, which is not the case.
02:23
@DanielFischer
r9m
r9m
02:51
Alrighty then !!! .. added a bounty on head ... wanted DOA
03:38
Do the reals contain a minimal integral domain?
@Ted naw, not hiding, out eating at mexican restaurants :3
@Ted two lines in $\mathbb{P}^{2*}$ correspond to pencils in $\mathbb{P}^2$, and their point of intersection corresponds to the line common to both pencils, yeah? ...But what's it mean when the two lines in $\mathbb{P}^{2*}$ are parallel? Then their point of intersection is at infinity and...bwuh?
03:57
What does $\mathbb{P}^{2*}$ represent?
the dual to the projective plane
04:40
Damn. Another night without sleep. Oh well, Galois Theory was too interesting anyway.
Better get ready for school.
@AndrewG The dual?
05:44
@MikeMiller its dual space. The space of lines in $\mathbb{P}^2$. Every point corresponds to a line, a line corresponds to a pencil of lines, etc.
 
4 hours later…
09:23
@r9m lol...no one will answer you :P :P
@DanielFischer Hey.
Hey @Sawarnik.
@Sawarnik No, as user1337 pointed out, $\xi$ depends on $x$. However, since $x^2 \geqslant 0$, there is a $c\in (-1,1)$ such that $$\int_{-1}^1 x^2g''(\xi(x))\,dx = g''(c)\int_{-1}^1 x^2\,dx,$$ since derivatives have the intermediate value property.
09:57
let A be an infinite set, F a field, W the vector space of functions A->F, U the subspace spanned by characteristic functions of subsets of A, and V the subspace of functions with finite support. does dim W = dim U? is dim U > dim V?
10:42
drats, the kernel of $\bigoplus_{2^A}k\to\prod_Ak$ has dimension $2^A$
Heya @blue
heya
Fun things happen if one considers Fix_Gal(L/K)(A). For example, you are really looking at Gal(L/K) acting on A by automorphisms so as the very first thing you get is a representation Gal(L/K) --> Aut(A) and if you let A to be some direct product of copies of Z_p then you get a representation Gal(L/K) --> GL_m(F_n)
Plouffe's copy of Artin
11:10
@blue I think if $|F|$ is at a certain sweet spot (near $|A|$) then you get the cardinality of $W$ to exceed the cardinality of $U$, let alone dimensions.
 
2 hours later…
13:05
@AndrewG Andrew, first of all, parallel makes no sense in the projective plane. What you are thinking is parallel in $\Bbb R^2\subset\Bbb P^2$, which, of course, means that the lines intersect in a point on the line at infinity. In the case of such lines in the dual plane, say $\xi_1=0$ and $\xi_1=\xi_0$, these would correspond to the pencils of lines through $[0,1,0]$ and $[1,-1,0]$, respectively. And the intersection point $[0,0,1]\in\Bbb P^{2*}$ corresponds to the line $x_2=0$ joining those.
Hello professor @TedShifrin
I am trying to find a way to prove that $\log z \not \in \overline{\Bbb C(z)}$ in a geometric way. Probably one way is to note that the Riemann surface $w = \log(z)$ consists of a bunch of (countably infinitely many) sheets over $\Bbb C$ and is being cut through the branch from $z = 0$ towards infinity and pasted upwards so that a point near $z = 0$ which tries to traverse a clockwise loop winds continuously upwards in clockwise sense.
This implies the monodromy must be an infinite cyclic, i.e., $\Bbb Z$. Perhaps one can draw the conclusion by noting that $\Bbb Z$ has no composition series? It's still solvable in the classical sense though.
13:54
What does the 2*Pi*I/Log(-p-1) periodicity mean in this wolfram alpha calculation?
http://www.wolframalpha.com/input/?i=-p*%28-%28p+%2B+1%29%29%5E%28n+-+2%29
broken link
wolframalpha.com/input/?i=-p*%28-%28p+%2B+1%29%29%5E%28n+-+2%29
broken link again
@Balarka: Doesn't it suffice to say that any rational function has a finite degree?
this is the expression I entered in wolfram alpha: -p*(-(p + 1))^(n - 2)
@Mats: I can't figure out what you're talking about.
What are $p$ and $n$?
@TedShifrin -p*(-(p + 1))^(n - 2) has periodicity $\frac{2 \pi i}{\log(-p-1)}$
This comes from the complex exponential. What are $p$ and $n$?
13:59
p and n are just variables
Not integers or positive ...
this comes from a transform I have invented
n is integer, I forgot
So you need to make Mathematica know that or else it's going to use the complex exponential. If you have an integer for an exponent, then there's no multivaluedness here.
So the periodicity does not apply in my case?
But continuity is a chimera, as someone said.
Clear[t, n, k, i, p]
p = 2
coeff = {p^0, -p^1, p^1, p^2, p^3, p^4, p^5, p^6, p^7, p^8, p^9, p^10,
p^11, p^12, p^13, p^14, p^15, p^16};
nn = Length[coeff]
cc = Range[nn]*0 + 1;
Monitor[Do[Clear[t];
t[n_, 1] := t[n, 1] = cc[[n]];
t[n_, k_] :=
t[n, k] =
If[n >= k,
Sum[t[n - i, k - 1], {i, 1, k - 1}] -
Sum[t[n - i, k], {i, 1, k - 1}], 0];
A4 = Table[Table[t[n, k], {k, 1, nn}], {n, 1, nn}];
A5 = A4[[1 ;; nn - 1]];
A5 = Prepend[A5, ConstantArray[0, nn]];
cc = Total[
Table[coeff[[n]]*MatrixPower[A5, n - 1][[All, 1]], {n, 1,
"p" is the input
"cc" is the output
Bob
Bob
@TedShifrin can you suggest a book for probability
14:23
@Bob: There are a bunch available on-line that seem pretty good. The standard undergraduate texts seem to be Pitman and Ross. I'm learning/teaching the stuff for the first time this fall, using Ross.
@Mats: You use the word periodicity, but that's really wrong. $\log z$ is a multivalued function. It's not a matter of period. But when you have an integer exponent $n$, $z^n$ is unambiguously defined.
Bob
Bob
@TedShifrin can you provide me some link to download the pdf copy
No, but you can google Probability + any of Ash, Grinstead/Snell, Bertsekas and Tsitsiklis.
15:01
@TedShifrin If I can transform $5 x+\frac{1+7 x}{1+6 x}$ into $\frac{1+x}{1-5 x}$, is it progress?
More generally the transform, transforms:
$$-\frac{1+p (-2+x) x+p^2 x^2}{-1+p x}$$ into $$\frac{1+x}{1+x+p x}$$
15:39
@TedShifrin I am talking about $\overline{\Bbb C(z)}$ not $\Bbb C(z)$.
15:49
Well, perhaps having infinite number of galois conjugates (equivalently, sheets) is just enough. I haven't seriously thought about it.
If it is true (which it obviously is, I just don't know how to prove it), then we get transcendence of infinitely many (and Zariski dense!) elts $\log(\zeta)$, $\zeta \in \Bbb C$ for free, by Hilbert's theorem.
 
2 hours later…
17:26
Hi MathSE people! May you help my soul, please?
18:07
@DanielF: Question for you that's arising in a colleague's work, and I'm feeling stoopid. What's an example of a harmonic function on the unit disk, continuous up to the boundary, whose harmonic conjugate is not continuous up to the boundary? What conditions will rule this out?
Oy, @Ted, I'm not sure that is possible. Gotta look closer at the Poisson integral whether I can see a way.
I somehow thought it would be a well-known regularity result if it were true in general. I found a comment on SE earlier that suggested there are examples. I'll see if I can find that.
@DanielF: Here's the comment.
18:31
Ok, I know I'm one step before I should get banned as a spammer, but I really need an answer quickly! mathoverflow.net/questions/173524/…
@nullgeppetto MO is for research questions, AFAIK.
@BalarkaSen, yes you're right, but I was desparate...
So that question would probably be locked before getting answers.
I give a link to my first MathSE question, here...
What do you suggest to me to do?
@nullgeppetto Have patience.
18:34
@BalarkaSen :)
Please tell the same to my supervisor!
@TedShifrin Ah, it is possible. As long as you don't want an explicit example, take a biholomorphic mapping of the unit disk to $\{ x+iy : x < 0, \lvert y\rvert < e^x\}$. The imaginary part extends continuously to the boundary, the real part doesn't.
@BalarkaSen, it's kinda irrelevant, but I feel like my (probably stupid) questions get lost after some minutes, as newer ones appear...
@nullgeppetto Yes, new questions appear in front of all the questions when you open MSE up.
@BalarkaSen, :), yeah, I know.. So, that's why I act like that, which is probably wrong, I know...
Interesting @DanielF. I was just down in the library looking at PDE books and didn't find any results ...
I'm not understanding your example yet, @DanielF.
Modulo knowing what the Riemann mapping looks like, @DanielF, I guess it's plausible, but I don't have a nailed-down proof.
@TedShifrin You need a holomorphic map on the unit disk such that the imaginary part extends continuously to the boundary, but the real part doesn't (or vice versa). A biholomorphic mapping between the disk and some other domain extends continuously to the nice enough boundary points. So I took a domain with piecewise smooth boundary such that it is unbounded in one direction, but the imaginary part has a limit as the real part tends to $-\infty$.
Right. I get that :) I see that the real part can't extend continuously. But is it clear that the mapping is sufficiently well-behaved that the imaginary part must?
Map it to a curvilinear triangle with one angle zero in the plane by a Möbius transformation. I'm almost sure the Riemann mapping extends to a homeomorphism of the closures then. Gotta look up Painlevé-Warschawski to be sure, though.
OK, I get it. We're looking at an annulus, of course, with piecewise smooth boundary. I wonder if there is any bounded counterexample like yours. (Actually, what we're discussing is a Dirichlet problem on an annulus with $u=0$ on one boundary and $u=1$ on the other. Then the question is whether the harmonic conjugate of $u$ (modulo period) is continuous up to the boundary.)
18:57
@PedroTamaroff
Ah, well, @TedShifrin, not Painlevé-Warschawski, but Carathéodory.
Yes, that name has come up several times today.
@TedShifrin The solution for the Dirichlet problem on an annulus with these boundary values is $c\log \lvert z-a\rvert - d$, where $a$ is the centre of the annulus, the conjugate is basically $\arg$, which has no problems with the boundary circles, but has a problem on some radius (or other curve connecting the boundary circles).
19:17
Right, that's why I said mod periods. Of course, our annulus isn't a round one :) Thanks for thinking !
@TedShifrin I'd think that if you cut it open along a "radius" and map it conformally to $[0,1]\times [0,2\pi]$, then the solution of your Dirichlet problem is the real part of that biholomorphism, and the map extends continuously to the boundary.
> Although it is known that the set of irrational numbers is greater than the set of rational numbers, is there any usefulness/applications of this fact outside of mathematics?
People have the strangest questions.
@DanielFischer Don't invite irrational people to your party. They will eat you out of house and home. Invite nice rational people; they are much more, uh, countable.
Well, @DanielF, I suppose constructivists are bothered by such sorts of philosophical questions :) hi @robjohn
@robjohn: They're still damned expensive.
@TedShifrin hey there...
Constructivists, deconstructivists, I'm not a fan of French postmodernism.
19:29
Let's face it, @DanielF. You're just not a fan of French.
Speaking of which, what's become of our French lads?
@TedShifrin but far less so than the others.
Maybe you have cheaper friends than I, @robjohn :D
@TedShifrin Oh, I am. I like good food. And occasionally a good wine.
These days you just settle for a good whine, just like @Mike :D
19:47
Hi, why Frenchman are famous for analysis in Math?
Huh @Ted?
@user18481 Presumably because they have done very good work in analysis.
@DanielF I think the best postmodernists were American or English.
@DanielFischer You beat me to it.
@MikeMiller "best postmodernists" has a definite smell of oxymoron.
@DanielF Perhaps you and I have different taste.
19:54
Greetings
@Chris'ssis Do you mean you are greeting me or that it is greetings to everyone or that you greet regardless of whether I take it or not or that you are greeting simply to be greeted back?
=P
@BalarkaSen I didn't say "Greetings" specifically to a certain person. So ... :-)
Yoroshiku minna!
@Chris'ssis I was joking. A similar joke is in the beginning of The Hobbit. You might not have read it though.
@BalarkaSen I know I know :-)
19:58
I found this interesting problem on Facebook. Don't ask why I was there. I don't even know. $$ \displaystyle \lim_{n \to \infty} \dfrac{\log(n!)}{\log(n^n)} $$
@BalarkaSen by the way, when will the last part of the Hobbit appear?
@Chris'ssis I have only read the books.
@Shisui Do you know Stirling's formula?
@Shisui Stirling.
Gah, @DanielF beat me to it. Again.
@DanielFischer It sounds familiar ...
19:59
@BalarkaSen Ahhh ... (I was thinking you watched the movies)
@Shisui Cesaro-Stolz
@Chris'ssis The hard way.
@BalarkaSen lol, is that hard?
$\log(n!) = n\log(n) + O(\log(n))$ and be done.
@BalarkaSen Maybe it is hard for you. Using this, any kid in high school can finish it.
@Chris'ssis Yes, it is hard for me.
I was not speaking in general.
@Chris'ssis Well, respective to Stirling...
Ah, well. Both are elementary -- one is a bit too tedious to me. I won't go in mathematical philosophy again.
20:05
@BalarkaSen I'd probably use that too, but for a beginner I'd recommend Cesaro-Stolz.
@Chris'ssis I know. I just don't do soft analysis. Asymptotic approximations are my thing.
(in this case, Cesaro-Stolz theorem combined with the mean value theorem)
@BalarkaSen Sure, that's OK.
Heya @TedShifrin
hi @Balarka
@Balarka: Your Stirling is in error
@TedShifrin Heh. error
$\log(n!) = n\log(n) - n + O(\log(n))$
20:09
Correctamundo.
What I always like to think is that prime number theorem is really striling with primorials.
Let me propose a new beautiful question ...
@BalarkaSen Hello.
You called.
$$\sum_{k=1}^{\infty} \sum_{n=1}^{\infty} (-1)^{k+n} \frac{\log(k+n)}{(k+n)^2} $$
@PedroTamaroff Yes. I solved your problem.
20:21
The one about solvability being preserved under extension?
Yes.
Suppose G is extension of solvable group N by solvable group K.
Ok.
It suffices you show that if $G$ has a normal subgroup $K$ such that $K$ and $G/K$ are solvable, so is $G$. I take it you did this.
Then consider the canonical map G --> K. elts of G^(n) are products of commutators of pairs of elements of G^(n-1)
@PedroTamaroff Yes.
Now note the homomorphisms take commutators to commutators.
20:24
Yes.
So the image of G^(n) in K is a subgroup of K^(n)
Since K^(k) = 1 for some k, G^(k) = 1
And you have solvability by definition.
This seems like an important result, yet though somewhat easy. I can now prove, for example, that semidirect product of solvable groups is solvable -- which is a fun fact!
@BalarkaSen This looks fishy.
@PedroTamaroff Hmm. Which step?
mr @Pedro: So, glad to see you've survived your horrid aging process :)
@BalarkaSen Well, no, it's wrong.
20:29
@PedroTamaroff Explain where I have messed up.
That would show that if $G$ is any group, and $H$ a solvable group, and $\eta:G\to H$ and epimorhism, $G$ is solvable. But we always have an epimorphism $G\to 1$; the trivial group.
You know that $\pi(G^{(i)})=1$ for some $i$.
That doesn't mean $G^{(i)}=1$.
@TedShifrin Hehe. I got my combinatorics tests back. I passed, as I thought, but barely. Prof. said I should pass my make up exam "properly" i.e. >50%.
You need to use $K$ and $G/K$ are both solvable.
Maybe you should stick to analysis, @Pedro :D
I'm terrible at discrete math ... that's why teaching probability is skeering me.
@TedShifrin I really want to be able to read Stanley's "Combinatorics and Commutative algebra." =D
@TedShifrin >:(
Oh, Stanley did all sorts of beautiful interplay between combinatorics and algebraic geometry (combinatorial hard Lefschetz theorem)
You'll be fine, @Pedro.
@PedroTamaroff Hmm.
20:32
@TedShifrin I don't know what the Lefschetz theorem is, but I'm really interested in combinatorics.
Even though I'm a bit slow at it. =)
It's about the cohomology (intersection theory) structure of algebraic varieties, @Pedro.
@BalarkaSen Do you see it?
@TedShifrin OK. Dunno about it. At any rate, yet again I missed a silly problem.
HI everyone
Did I ever tell you about my test grades when I took abstract algebra my second year in college, @Pedro? They went 100, 77, 58.
That was first semester.
@PedroTamaroff I am seeing it.
20:34
@TedShifrin Oh. Did something happen to you there...?
Yeah, I sucked at algebra, @Pedro. But I survived and learned it eventually.
Drugs? @TedShifrin
oh
@BalarkaSen For the proof, suppose you have solvable series for $K$ and $G/K$. Then show you can patch them up to get a solvable series of $G$.
It is not hard.
Nope. I didn't do too well with group actions and Sylow Theorems at first. And I messed up a linear algebra proof on that third test, too ... :(
@PedroTamaroff I am trying to stay out of solvable series
20:34
And indeed solvable series (instead of derived subgroups) work better here.
@BalarkaSen Don't. The more tools you have, the better!
@PedroTamaroff Exactly the same thing my professor says.
What uni were you at for undergrad? @TedShifrin
MIT, @JohnDoe. Many centuries ago.
@TedShifrin lived for almost 300 years, @JohnDoe
@TedShifrin Well, hehe. In this test, first I showed that if $P$ is a poset with $n$ elements, then it has either a chain of $\sqrt n$ elements, or an antichain of $\sqrt n$ elements. I proved that nicely. Then second item was showing that if we have $50$ distinct sets one could pick $8$ such that in no set is the union of another two in such collection. I didn't realize $\sqrt 50>7$. =/
20:37
61 is only his 'official' age, to cover up the fact that he is one of the Wise that live in Orthnac.
The second sounds like pigeonhole ...
Well, yes.
It is pigeonhole.
How many of those years has he been studying maths?
Using pigeonhole, one can show that in any graph on $n$ vertices $\chi(G)\alpha(G)\geqslant n$, @TedShifrin.
20:38
It's the deep math that always trips us up, @Pedro. Like $50>49$.
Then take the comparability graph of the poset $P$, and profit.
@TedShifrin Exactly.
Do you know if Indiana state university has a good maths department? @TedShifrin
@TedShifrin Partial orders are freaking hard.
Where did you do your postgrad studies? @TedShifrin
Indiana State? As opposed to Indiana Univ Bloomington?
I know no one at Indiana State. That proves nothing, but it is not well known.
Berkeley, @JohnDoe.
I only think about them if they arise in some interesting context, @Balarka. I'm not a very set-theory oriented person.
20:41
@TedShifrin I was talking about $50 > 49$
LOL, oh ... Nah, that's a linear order, not a partial one.
I always have trouble with pronunciation. People laugh at me when I say "Cayley's theorem"
KAI LEES.
Kelly, yeah. I was told that by someone.
@PedroTamaroff Stop pronouncing Japanese.
Where is everyone else studying @PedroTamaroff and @BalarkaSen ?
20:43
Kai is ambiguous, @Pedro.
@TedShifrin "K"?
@JohnDoe I am studying nowhere.
no, K like the letter ...
@JohnDoe I'm in Argentina, as my profile says.
Room is basement is an acceptable answer...streets also @BalarkaSen
20:44
When I said "quintic" people positively laughed at me.
@PedroTamaroff What uni?
Better to be laughed at positively than negatively!
I pronounced as KOAINTIC.
Room in basement that is
@TedShifrin Heh.
20:45
kwin = koain?
@JohnDoe UBA.
@TedShifrin No.
c c
c c
I'd have said "queentik", but maybe "keentik" is good
@PedroTamaroff You following the world cup?
@cc that's the correct spelling.
queentik.
20:46
@JohnDoe Slightly.
@PedroTamaroff Messi is too messy.
c c
c c
Angel is too angelic
Angle is not an angel, for finding sines can be a tangle.
rolls all six eyes
@TedShifrin Great spiders of Mirkwood!
20:49
My grandmother asked me who I was talking about when she read my grade 4 book it said 'a cute angel'...true story...I just shouted 'fucking context'
@BalarkaSen It's a cool problem
@PedroTamaroff Well, I can't disagree.

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