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6:00 PM
I have to think.
You can't expect me to be good at these things, I have no practice.
 
I can give you a hint: show that if $s\in (1,+\infty)$ there is a compact neighborhood of $s$ bounded away from $1$, and use that you have a sum of continuous functions and the sum is bounded above by a convergent series.
 
But I will try.
 
{0., ComplexInfinity, ComplexInfinity, ComplexInfinity, ComplexInfinity, 0.}
For zeta zeros 1 to 6
 
@MatsGranvik I doubt that you could use $\infty$ and $-1$ interchangeably.
 
@robjohn ok
 
6:03 PM
@MatsGranvik I do not understand what that means. Are they residues?
 
This is the code:

Clear[s, n]
Monitor[Table[
N[Limit[Zeta[s]*(Exp[Total[1/Divisors[2]^(s - 1)]/Zeta[s]] - 1),
s -> ZetaZero[n]]], {n, 1, 6}], n]
I set divisors to 2, just to see if there is any pattern.
 
6:17 PM
@Pedro I have an idea.
 
@BalarkaSen OK.
 
I will post it after I am done eating.
Just hang on for that while.
 
1 hour ago, by Pedro Tamaroff
user image
hi @Sawarnik
 
hi
 
are you mad at me?
 
6:27 PM
why? o.O
 
r9m
@Sawarnik not talking to me .. whats up ?
 
dunno, you stopped talking to me
 
@Pedro Hang on, just there, eating Mike at super fast speed.
 
@r9m Nah...I was talking to others in the other room.
 
r9m
@Sawarnik okway :)
 
6:30 PM
@skullpatrol More or less, I stopped coming to the main chat here, nothing else. :)
 
ic ic
:-)
 
@MatsGranvik so you are trying to evaluate the limit of $\displaystyle\zeta(s)\left(\exp\left(\frac{1+2^{1-s}}{\zeta(s)}\right)-1\right)‌​$ as $s$ tends to a root of $\zeta(s)$.
It seems to depend on the direction that $s$ approaches the root
 
yes, that is the second limit. The starting point is this:
Clear[s, n]
Monitor[Table[
Limit[Zeta[s]*(Total[MoebiusMu[Divisors[n]]/Divisors[n]^(s - 1)]),
s -> 1], {n, 1, 23}], n]
Which I modified just by inspecting the numbers into this:

Clear[s, n]
Monitor[Table[
Limit[Zeta[s]*(Exp[Total[1/Divisors[n]^(s - 1)]/Zeta[s]] - 1),
s -> 1], {n, 1, 23}], n]
 
@Pedro I am most certainly sure that this is flawed, but let's see :
A plausible thing to do here is to consider uniform convergence, as that clearly implies continuity.
 
@robjohn I see now, Mathematica chooses somehow the direction of the limit.
 
6:39 PM
So we consider $f_n(x) = \sum_{k \leq n} \frac{\log k}{k^s}$
 
@MatsGranvik The limit seems to depend on how $s$ approaches the root. I don't think the limit exists in all directions.
 
Following, @PedroTamaroff, or gone?
 
@BalarkaSen Here I am.
 
OK, OK.
$f(x) = \sum_{k \leq n} \log k/k^x$ clearly converges in the given interval.
 
Hi guys, quick question. Is the direct sum unique? That is, is it true that $H = A \bigoplus B = A \bigoplus C \implies A = C$?
It seems to me it is, but I just wanted to check.
I'm sure it's true in finite cases, but would infinite dimension mess things up?
 
6:43 PM
Now, @Pedro, I remember you did something with the M-test here for uniform convergence, correct?
Now I believe I don't need it. Am I wrong?
 
@BalarkaSen You do need it! =D
 
@PedroTamaroff
 
@Ryker Direct sum of what?
 
@PedroTamaroff In my derivation, I didn't use it, I think.
 
@BalarkaSen You need to show uniform convergence somehow.
 
6:45 PM
Well, anything.
 
I used summation by parts.
 
Two sets.
 
(yeah, that's how a number theorist think)
@Ryker So that's direct product, no?
 
For example, if $\varepsilon>0,s>1+\varepsilon>1$ and $s\in[1+\varepsilon,s+\varepsilon]$, $$\sum_{n\geqslant 1}\frac{\log n}{n^{s}}\leqslant \sum_{n\geqslant 1}\frac{\log n}{n^{1+\varepsilon}}<+\infty$$
 
Oof, too much analysis. I simply used summation by parts.
 
6:47 PM
No, it's the direct sum.
 
Nothing less nothing more.
 
@BalarkaSen Too much analysis? Stop complaining! It is a simple inequality. If $s>1+\varepsilon$, $n^s>n^{1+\varepsilon}$.
Then you can use the Weiertrass $M$-test.
 
I won't. Won't won't won't won't won't.
See my summation by parts derivation.
 
And you get the sum converges uniformly on $1+\varepsilon\leqslant s\leqslant s+\varepsilon$, hence continuous at $s$.
@BalarkaSen OK.
@BalarkaSen So?
 
Writing, wait up.
$$\sum_{m \leq k \leq n} \frac{\log k}{k^x} = \frac{1}{(n+1)^{x+1}}\sum_{m \leq k \leq n} \log k - \frac{1}{m^x}\sum_{m \leq k \leq n} \log k - \sum_{m \leq k \leq n} \left [ \frac1{k^x} - \frac1{(k+1)^x}\right ] \sum_{m \leq k \leq i} \log i $$
My internet connection is not incorporating.
 
6:59 PM
@BalarkaSen OK, and what will you do with that?
 
Now we take absolute values on both sides.
 
Note the log gets turned into $\log(n!/m!)$
I don't find that particularily useful.
 
Oh, damn. I wrote up wrong there.
I meant
$$\sum_{m \leq k \leq n} \frac{\log k}{k^x k^y} = \frac{1}{(n+1)^{x+1}}\sum_{m \leq k \leq n} \frac1{k^y} \log k - \frac{1}{m^x}\sum_{m \leq k \leq n} frac1{k^y} \log k - \sum_{m \leq k \leq n} \left [ \frac1{k^x} - \frac1{(k+1)^x}\right ] \sum_{m \leq k \leq i} \frac1{k^y} \log i $$
It's just that the LaTeX is playing trickseys on me.
And so is the internet connection.
 
Too complicated.
 
Now you do that absolute value thingy.
 
7:03 PM
$$\sum_{n\geqslant 1}\frac{\log n}{n^{s}}\leqslant \sum_{n\geqslant 1}\frac{\log n}{n^{1+\varepsilon}}<+\infty$$
Done. =)
 
@PedroTamaroff Stop complaining, sire!
=)
 
@BalarkaSen I don't see how your method will yield anything useful! It just too messy. Let's agree on this one.
 
$$\left | \sum_{m \leq k \leq n} \frac{\log k}{k^x} \right | \leq \frac{1}{(n+1)^{x+1}} \left | \sum_{m \leq k \leq n} \log k \right | + \frac{1}{m^x} \left | \sum_{m \leq k \leq n} \log k \right | + \left | \sum_{m \leq k \leq n} \left [ \frac1{k^x} - \frac1{(k+1)^x}\right ] \sum_{m \leq i \leq k} \log i \right |$$
@PedroTamaroff Will you just see without complaining? Point out if I am wrong.
 
@BalarkaSen OK, what happens now?
 
@PedroTamaroff Now we choose an $\epsilon$ that bounds the both of the $$\sum_{m \leq k \leq n} \frac1{k^y} \log k$$ terms.
 
7:08 PM
No, you don't choose $\varepsilon$.
You choose $m,n$.
 
Yes, we find $\epsilon$
That is satisfied by certain large $m, n$
Correct?
 
@BalarkaSen No, you're given $\varepsilon$!
You have to choose $m,n$ given $\varepsilon$.
 
@PedroTamaroff let me put it this way : We find some large $m ,n $ s.t. a small $\epsilon$ bounds the sum.
Right or wrong?
 
@BalarkaSen The point is not that $\varepsilon$ bounds the sum, rather, the sum can be made smaller than $\varepsilon$ choosing $n,n$ large for any $\varepsilon$. Look it from right to left (i.e. the importance is in the sum) not from left to right (i.e. the importance is on somethign that bounds it)
 
I surely know this much calculus, don't you think, to put it straight?
@PedroTamaroff In any case, $m, n$ is the ones that we need to choose.
 
7:12 PM
@BalarkaSen Exactly.
 
(I might be bad at these representating things time to time, bear with me)
Now, where were we?
Aha.
 
I have to go.
Sorry.
 
Fine.
 
The point is the sum is continuous on $(1,+\infty)$. Yay.
 
But you can see where this will lead, no?
@PedroTamaroff Of course, so is any Dirichlet series with certain condiitons imposed (in which case, Perron! Fun, fun!)
But my point is that we don't need M-test.
No weirdo stuff.
Hello, @N3buchadnezzar
 
7:25 PM
Lol. Just read this thread on Meta.
We are amused.
@DanielFischer Hello.
 
Hi @MattN. Which thread on meta?
 
@DanielFischer Oh, I already closed the tab. Someone seriously posted a thread complaining that some questions were too long. But funnier than that there was a (now deleted) answer suggesting adding a new close reason "too much effort".
Even typing it still gives me the smiles : D
 
Ah, that one. I remember ;)
 
But, funnier than the already funny thread, the poster of the deleted question (too bad I didn't get a chance to downvote) is not a new user and whatever name he puts on his account his unpleasant personality shines through brightly.
And now this guy posted a comment telling someone else that they were unpleasant.
Not in these words but that's the gist.
So now I am quite amused.
 
@DanielFischer Got an ENT for you. Interested?
 
7:31 PM
And I just couldn't help posting a comment. I felt that Bill was wronged there.
I mean, Bill is quirky. At best. But this other guy is properly unpleasant.
 
@BalarkaSen Can't tell without seeing it.
 
Count the number of solutions $(x, y)$ of $$\frac1x + \frac1y = \frac1N$$ for some fixed $N$.
@DanielFischer Combinatorial problem mostly.
 
A classic, @BalarkaSen. $$\frac{1}{N+d} + \frac{1}{N + \frac{N^2}{d}} = \frac{1}{N}.$$
 
@DanielFischer You don't have to answer if you don't like but I was wondering if you ever did a PhD.
 
I didn't, @MattN.
 
7:37 PM
Oh wow.
Scary. I was pretty sure the answer would be yes.
@DanielFischer Now I can't ask you about your PhD :)) Too bad.
Oh well. I'll find another victim. : )
 
@MattN. You could ask Ted, I'm pretty sure he has one.
 
Darn my internet.
@DanielFischer So the solution is.
$\tau(N^2)$
 
@DanielFischer Thanks, I will -- next time I see him here.
 
Well done.
I did a bit differently though.
 
@BalarkaSen Or $(\tau(N^2)+1)/2$, if you don't distinguish $(x,y)$ and $(y,x)$.
 
7:41 PM
Yes, modulo the symmetric equivalence $\sim$, that.
But I didn't want that.
I did it by counting $$\sum_{a|N} \sum_{b | N/a} 1$$
(At least, one of the many solutions)
Another classic is $(N - x)(N - y) = N^2$
But I don't like trick theory.
My counting trick is the most analytic non-tricky way I can think of.
 
7:58 PM
hello, i'm sorry to do this but can you help me :math.stackexchange.com/questions/718143/…
?
thank you
 
8:09 PM
I'm skimming the table of integrals series and products by Gradshteyn and Ryzhik for half an hour and nothing interesting. I wonder if it's something wrong with me ...
 
light reading :D
 
@skullpatrol :-)
 
@Chris'ssis There is definitely nothing wrong with you, it sounds like you need something more challenging.
 
Is there a noun associated with usages of capital pi notation, the way sigma notation has 'summation'? I'm tempted to call it a 'productation' but google only finds a few references to this term ever having been used...
 
@skullpatrol There is a thing I admire for some time, this one: math.stackexchange.com/questions/464769/…
@skullpatrol I hope to be able to prove that sometime by real analysis.
 
8:19 PM
@Chris'ssis Thanks :-)
@0x5f3759df how about "factoration"?
 
I thought about that, but every reference to that I can find is just a misspelling of 'factorization'. Productation actually has a few uses in literature but it's nowhere near common. I was hoping there was a non-obvious standard I wasn't aware of.
 
producation sounds interesting :-)
 
Why can't people write properly anymore?
Seriously, if what you're writing wouldn't make sense if you walked up to somebody on the street and said it to them, it's probably wrong.
Just saying.
Okay, rant done.
This is Math StackExchange after all, and not the grammar police.
Yeah...
 
8:34 PM
too fast
 
Hey.. I was playing a game while reading that. Unfortunately my opponent was still more error-prone than me.
 
@robjohn can you help me ?
 
@Vrouvrou what's up?
 
9:26 PM
What's the relationship between modules and non-abelian groups? (since abelian groups are just Z-modules, etc.)
 
@AndrewG A way to express $M$ as an (abelian) $R$-module, is to give a ring homomorphism from $R$ to the endomorphism ring of $M$. Since the set of endomorphisms of a non-abelian group does not necessarily have commutative "addition", it would be incorrect to say it is a module over a ring.
(I think one of the distributive properties fails as well, but this is a result of the addition being noncommutative)
 
@Vrouvrou Is there some reason it is not as simple as my answer?
 
9:45 PM
@AndrewG That said, one can feel free to define "modules" over a weaker type of ring by using the definition I gave and defining homomorphisms the same way we do for rings. The problem is that the homomorphic image of an actual ring will be an actual ring, so I do not see any real gain here.
 
Howdy @robjohn @Karl @AndrewG
 
@TedShifrin Hello
 
10:02 PM
@Ted hi :) @Karl thanks
 
Haven't seen you in a while, @Andrew!
 
Yeah, I've been knee-deep in classes. How have you been?
 
Doing ok, thanks ... Torturing students as always :)
 
Hi @Andrew, been a while
 
:) glad to hear it. I've been mathing on the side, but gen eds are eating up most of my semester. Have to read another 100 pages of lit tonight.
heyo Mike!
 
10:10 PM
Yuck gen eds. I feel ya.
 
I still believe in liberal arts education, sorry, guys.
Should spread it out liberally, however.
 
I'm actually enjoying it -- got Joseph Conrad's Heart of Darkness and Kafka's Metamorphosis tonight -- it's just really time-consuming.
 
@Ted I believe in it. It falls apart when I'm forced to take my third damn religion class.
 
Math is way time-consuming for most ...
We've been around this bush already, @Mike :D
 
@Ted I have a trivial topology question for you.
 
10:14 PM
Trivial topology is boring.
 
Well, i'm off for dinner. Good seeing you both again :)
 
See ya @Andrew
 
I can't prove locally path connected and connected implies path connected.
The intuitive picture is obvious but I can't make it a proof.
 
user58869
what does proof mean?
 
Oh, standard connectedness game. Look at the set of points pathable from $x$.
 
10:17 PM
Oh. Done.
 
Yup. :)
 
user58869
also, how can i learn to understand the mathematical notation used so much by people on the mathematics stack exchange site and also no wikipedia?
 
@Karl I have a question for you
 
@Mike sure
 
user58869
10:19 PM
every time i try to read something on wikipedia, i come up to an image that i dont understand and i am lost at that point
 
Hmm, is there an on-line notation glossary? I put this sort of thing as an appendix in my books.
 
@Karl I was gonna make a 5#2 joke but meh
 
@Alex what math do you know? The usual answer is 'read a book', but without more information I can't recommend one.
 
user58869
0
Q: how can i learn about mathematical notation

Alexi am baffled by mathematical notation. i think that if i could understand it then lots of things that i read would make sense. how does one learn this? i went to school, i attended maths lessons, but perhaps i didn't listen at the right time or maybe i was at a dentists appointment when they d...

 
10:23 PM
You're going to need to answer my question, either there or here.
 
user58869
@Mike which book? i imagine that once upon a time you did not know how to understand the mathematical notation, but now you do, so i need to get from where you were to where you are now in that respect
 
@Alex My point is I can't say. What math do you know? That's our starting point.
 
user58869
@Mike it's hard to answer that, i can tell you what i dont know, i dont know the notation
 
user58869
i read it all the time, but it means nothing
 
user58869
how can i understand it
 
user58869
10:25 PM
the symbols
 
user58869
wait i'll find an example
 
@Alex Have you used the glossary or index to look up notation?
 
user58869
this
 
@robjohn Have you seen this one before? $$\int_0^1\int_0^1 \log\left(\log\left(\frac{1}{x y}\right)\right) \log\left(\frac{1}{xy}\right)^{s} \ dx \ dy$$ I just created it (that doesn't mean I'm the first one that did that).
 
user58869
10:26 PM
 
user58869
what is that?
 
@Ted I did universal coefficients for homology today. Tor is scary.
 
@Alex It could be anything.
 
user58869
@skullpatrol what glossary?
 
@Alex In textbooks.
 
user58869
10:27 PM
@KarlKronenfeld that's exactly what goes through my mind when i look at it
 
@Alex You have to take into account its context.
 
user58869
@skullpatrol where do i begin
 
At the beginning :-)
 
user58869
ok... i'm sorry everyone, i'm an idiot
 
of the book
 
user58869
10:28 PM
bye
 
later
:(
 
I assume he's a kid, he'll learn
 
the problem is too common
 
the issue is you can't say where to start if you don't know where he is
 
@Mike mabye he just doesn't have experience reading math books.
 
10:32 PM
that has nothing to do with what I said
he has experience with some education system (I hope)
 
But to get gain from experience you need experience...that's what you wanted to know: how much experience do you have ie What math do you know?
 
@Mike Having experience with an educational system and having experience self studying from a math textbook are not the same thing.
 
true dat^
 
@Chris'ssis never seen it before. Does it have a nice closed form?
 
@user4140 which is, again, not what I said.
 
10:43 PM
@robjohn It should be $\Gamma(s+2) \psi(s+2)$ if I didn't miss anything there ... although I have a strange feeling and want to see again my calculations.
 
@Chris'ssis have you checked these numerically?
 
Oh, I thought your last comment was aimed at me
 
@Chris'ssis that is a good test
 
@robjohn I was inclined to believe this is true for all $s>-2$, but around the point $-1.4$ I begin to have some issues there.
 
@user4140 in a busy chat like this one, it is best to use the arrows that link to the comment you are replying to.
 
10:45 PM
@robjohn thanks for the tip
 
@robjohn Numerically, for $s\ge-1.3$ (approximately) things are OK.
 
@Chris'ssis I imagine it is probably okay for $\mathrm{Re}(s)\gt-2$, but numerically, it may be unstable near there
 
@robjohn Yeah. At any rate tomorrow morning I'll check again all my work to see if I missed any important point.
 
Hey @JasperLoy what's going on?
 
@skullpatrol I just woke up from a nap.
 
10:52 PM
@robjohn For $s=-1.5$, Mathematica says NIntegrate::inumri: "The integrand Log[Log[1/(x y)]]/Log[1/(x y)]^1.5 has evaluated to Overflow, Indeterminate, or Infinity for all sampling points in the region with boundaries {{0.,3.97545*10^-31},{0,1}}"
 
mga
Hello nice people. May I ask a quick question about self-learning?
 
askaway
:-)
 
@robjohn This evening I conjectured an interesting fact about this integral family, namely: if we consider the multiple integral version with $n, \space n\ge2$ variables, then we get something like $\displaystyle \frac{1}{n-1} \Gamma(s+n) \psi(s+n)$. I'll have to check that one more time to be sure it's like that. (tomorrow)
 
@mga Of course not.
 
mga
Cheers. So I have an engineering-style math education. I just want to know how monumentous a task it would be to go through a good Real Analysis course, say Rudin. Is it doable, or am I being over ambitious?
 
11:00 PM
@mga Which Rudin?
 
mga
Baby Rudin, as I understand it's called :)
 
To be perfectly honest, you're in way over your head, just kidding :-)
 
@mga If you have some talent in math, it's OK. Otherwise, it's tough working on your own.
 
mga
I always got very high grades in math courses in engineering, but whether that will actually translate into doing proper math I guess remains to be seen.
 
How much learning have you done on your own?
 
mga
11:03 PM
But I am correct that analysis is an absolute must for any one wanting to learn mathematics properly, right?
 
@mga Well, nobody can answer your question here, because we don't know your math skills.
@mga I would say it is fundamental.
 
mga
@JasperLoy Sure I appreciate that you can't give me a tailored answer. :-)
 
@robjohn For the general case with $n$ variables I think it's $$\displaystyle \frac{1}{(n-1)!} \Gamma(s+n) \psi(s+n), \space n\ge1$$
 
mga
I'm decent, but I don't think I'm a prodigy. I have a PhD (in engineering) though, so I'm used to having to learn stuff on my own.
 
Electrical?
 
mga
11:05 PM
Yes.
 
@mga Hmm, why don't you just pick up the book and start and see how you go?
 
mga
@JasperLoy Sure. Just wanted a quick opinion of others first.
 
I agree with Jasper :-)
 
@mga Anyway, what made you choose Rudin? Just want you to know there are many equally good alternatives.
 
mga
Everyone seems to rant on and on about Rudin and sing its praises, it seems to be "the" textbook.
Do you have any other favourites?
(Another factor is that I could find several sets of solutions.)
 
11:07 PM
Well, you can look at Browder's Mathematical Analysis, Pugh's Real Mathematical Analysis or Protter's A First Course in Real Analysis as well.
 
mga
To be honest when doing self learning going through books is hard; choosing the books is harder.
So cheers for the suggestions.
 
It takes a lot of determination to stick with one book.
So choose carefully.
 
mga
I'll try Rudin first - if I find I can't handle it, I'll consider alternatives. Thanks for your help both.
 
2 mins ago, by mga
(Another factor is that I could find several sets of solutions.)
this ^ is important
when you're on your own
 
mga
Indeed - probably one of the most important factors in fact.
 
11:11 PM
:)
 
mga
Though math.se always helps.
Anyway, enough wasting your time. Thanks again.
 
good luck!
 
That will be 100 dollars.
 
I was wondering if anyone could help me with my problem. math.stackexchange.com/q/720284/128346
 
each
+ tip :D
 
mga
11:15 PM
@JasperLoy If you close your eyes and believe really really hard it should appear on your desk.
 
@mga There can be miracles when you believe.
 
mga
;)
Good night!
 
later
 
@JasperLoy Isn't that anons phrase?
 
@user4140 It is my phrase, sorry.
 
11:17 PM
really?
Sorry in that case
 
It is well known in this chat that it is my phrase.
 
no it's Mariah Carey's phrase
 
Yes, and then it became mine too, lol.
 
you just want her, admit it
 
True dat.
 
11:19 PM
:D
 
How does one evaluate finite sums using residues?
 
I can't advise it
 
I've heard that it's doable, though I still don't see how it makes anything easier.
 

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