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00:00
(and on that question, that's funny. OP didn't seem to like it)
@tb It had pretty pictures :-)
Random personal comment, since we're talking about the Philippines: @J.M., did I ever tell you that I lived in the Philippines? It was for about two years - all before I turned three. So, unfortunately, I don't remember any of it. I wish I did.
@JM I agree.
@JM A few hours ago I gave two links to Mike Spivey where the exact same joke came up in connection with Arturo.
@robjohn Oh, thanks, I can't produce cartoons on the level of JM's, but I think I know how to make pretty pictures with geogebra!
@MikeSpivey Nope, interesting! You're an army brat, by any chance?
@tb I love your Geogebra pics. It was Aryabhata who started the trend, right?
00:05
@JM Good guess! Air Force, actually. Dad was stationed at the air base near Manila that I believe was destroyed by a volcano about 20 years ago. My sister was born there.
Dad got out of the Air Force about three years after leaving the Philippines and spent the next few years as an engineering prof.
Wow... that volcano was a looong time ago. :)
@JM: I don't think so, here he asked me how I produced them and that he would download the software. And here are the Chuck links
Aw, I've seen those; I thought there were new "Arturo is so badass..." jokes.
(and thanks, by the way!)
Can you do more than just circles and lines on Geogebra?
00:10
I see I had it backwards. :) I was once using Geometer's Sketchpad for those purposes (including assisting kids with less than stellar imaginations).
@anon: Oh, yes, it's incredibly powerful. Check it out, it's fun.
I think this is the first time I've ever seen the same question tagged "combinatorics" and "differential equations."
I get it, I get it, jeez. Stop pinging me! :)
Well, Robert did reply with a GF approach... :)
@anon: talking about spam. (sorry, I forgot that each edit triggers a ping)
00:12
@JM True. I think I'm going to remove the diff eq. tag, though.
Yeah, I don't consider Rodrigues's formula to be a DE myself...
Gotta run... Catch all of you later.
@Mike: see you!
See you!
The first comment here gives me a headache...
@JM Well, I see the real numbers as Dedekind cuts and the rational numbers as fractions, which, in my view, aren't numbers either.
00:17
:) Helluva rejoinder...
It's all just various algebraic structures anyway, the ones sufficiently closely connected with our original idea of numbers and the trend of expanding generalizations get the label "numbers" in the end.
Eh, I'm pragmatic. As long as they do what I want 'em to do, I don't care much for what they love being labeled...
Anybody want to help me parse "You might want to add that the bulk of the real numbers are numbers that you can't actually define in anyway."?
@JM Well, maybe you find anyway to answer that problem by the ratio of ratio.
The funny thing is that simplicity's comment to the question itself acknowledges that i is a number. Then he flip-flops completely on Adam's answer.
The questions I'm having after reading that last article sound more philosophical than mathematical. I think I'll pass for now.
good point Henning
Gee. For once, I like my answer better than Robert Israel's
I have a feeling that all of the answers to "what is a real number" are several levels of abstraction higher than what the OP was looking for.
3
00:28
That's the impression I got as well.
A real number doesn't cry at chick flicks.
Hm, no, he actually liked the "completion of Q" answer. So my dumbed-down attempt goes to the bit bucket instead.
Huh? Leave it, it might be useful for other people...
Okay, undeleted on popular demand.
@Henning: may I suggest that you add links to the words you mention? That might make your answer much more useful (a click is easier than entering the words in Google, which, in turn, is harder than asking a question here, but I like to think the click is still the easiest among the three)
00:41
Yeah, since this is, as you say, the kid-gloves version, linkery would be helpful.
Good point. Done.
Thanks!
Neat!
00:57
OMG! I had looked at Does this question even have an answer? when it was first asked. I just looked and saw that it had 77 upvotes, 22 favorites, and Henning got 85 upvotes.
A genuine blockbuster...
@Henning: I hope those upvotes were spread over a few days.
I thought it was mildly amusing, but I guess I don't grok the mindset of the masses here.
Man, we are getting a lot more traffic. The last question listed on the front page was last touched three hours ago.
If we hit the point that it's "one hour ago", I'm gonna have to start filtering.
@robjohn They capped out the first few days, but have been coming steadily since then. My eyeball estimate is the there's a 50/50 chance that the tail-end upvotes will bring it to 100 eventually.
@robjohn Don't try; you'll just go bonkers.
01:03
@JM and I'm not already?
There's a single downvote too. Unexplained, of course. rages and froths
There are 3 downvotes on the OP
@robjohn Touché. *facepalm*
Hee hee, ho ho, haha
The OP got a comment explaining at least one of the downvotes, though.
@robjohn there is even a dedicated meta thread for that question.
01:09
I see. Social phenomena are unfathomable sometimes.
Gotta run to the park for a while. bbl
@anon: prolly no use arguing with Kronecker there... ;)
what?
I mean "simplicity". Have you seen his last comment?
It appears his last comment is chronologically before my last comment, so yes?
I'm confused.
simplicity is confusing...
01:17
Not just his last comment. He must be having a bad day in general.
holy cow 100 active questions within the last 7 hours? This site's becoming too active for me.
Way more active than a few days ago. On the other hand, still within my threshold before I need to do filtering.
(I'd have missed the elliptic integral question if I didn't check page 2, for instance...)
Well, but >200 active questions a day is hitting the upper bound I can manage...
Speaking of which, didn't you say you've already started filtering?
Well, I've got a lot of faded-out tags, but I still display everything.
02:13
how do you filter? i just want to see active questions with my tags, but best i can get is highly upvoted unanswered questions or the whole shebang
Seen this?
@jm: yeah, but i have a lot of tags and i want to see the "OR" of them
How about this?
and this?
03:09
@jm: thanks! added to my list of bookmarklets: ms.uky.edu/~jack/mse.html
alo alo
So I've been playing with a problem for a bit, and I've hit a wall
I was hoping someone could give me the quick push I need
I'm trying to find a closed form expression for $\sum \frac{1}{z^3 - n^3}$
taken for n over all integers (z complex)
one would expect it to look something like $\frac{1}{sin(pi z)sin(pi \omega z)sin(pi \omega^2 z)}$
or something along those lines (up to addition by an entire function)
But I'd like to know what that function is - which is inconvenient
the big problem is that the sum isn't periodic, and my expression is
any ideas?
Why is the expression periodic? Don't the phase terms omega and omega^2 inside the "sin" affect the periodicity? @mixedmath
because each of the sin expressions are periodic
unless I
hmm - let me consider this before I respond - I didn't think so
03:25
I believe they do.
when you say they do, you mean they destroy periodicity?
mmhmm
Yes, I wrote "destroy", but changed to "affect".
if omega=sqrt(2), then it does. I think if omega=3 everything is ok
I'm sorry - omega is a cubic root of unity
03:27
@mixedmath The statement "A affects B" is so general that it's hard to be proved wrong, you see...
that's interesting - then that might even be the whole series
that is, it might be pi^3 over the product of the three sin terms
Does n range over N or Z?
I'll try a "reverse-engineering" approach
@anon I second that idea.
But why are the sin terms in the denominator? What's the taylor expansion of cosec x?
03:31
we put them in the denominator naively - because we know exactly the poles of 1/(z^3 - n^3)
it has simple poles at Z, omegaZ, and omega^2Z
where I use Z to stand for all integers and omega to be a cubic root of unity
That's a good start. Thanks.
One idea in the forward direction could be to write 1/(z^3 - n^3) as a partial fraction: A/(z-n) + B/(z-omega n) + C/(z - omega^2 n).
yes - it turns out that all coefficients are 1/n^2
it sounds like a very good idea, but the 1/n^2 coefficients are very bad in terms of closed forms, and I hit a wall
but perhaps it is possible to proceed from there
You're quite right, it's not obvious what to do from there.
Perhaps the Euler infinite product for sin(x) can help?
good idea
There's some eerie similarity: en.wikipedia.org/wiki/…
03:44
hmm, that gives (conjectured function) = prod_{n in Z} (1-(z/n)^3)^-1
Note that our first series can be written as \sum (1/n^2) (1/(z-n) + 1/(z+n)) = 2z \sum (1/n^2) (1/(z^2-n^2) )
@anon Doesn't the question ask about sum of those terms instead of product?
Sri: hell no, look at the terms. they go to 1 in the limit. but very similar, formally.
yes, but like I said I'm working backwards
@anon =).
also, I think you rewrote sum 1/(z^2-n^2), not sum 1/(z^3-n^3)
okay, I have revised my guess a bit
instead of just pi^3 on top, I want the respective cos terms, I think
03:54
this is weird (the 'result' part in particular): wolframalpha.com/input/?i=Sum%5B1%2F%28z^3-n^3%29%2C{n%2C30%2C30}%5D*Sin%5BPi*z%5D*Sin%5BPi*%28-1%2BSqrt%5B-3%5D%29%2F2*z%5D*Sin%5BPi*%28-1-Sqrt%5B-3%5D%29%2F2*z%5D
so that I get pi^3 * cos (pi z) cos( pi omega z) cos (pi omega^2 z) / (sine stuff)
i.e. pi^3 cot cot (omega) cot (omega^2)
oh - does it not like wolfram...
interesting
Okay, how bout this: Sum[1/(z^3-n^3),{n,30,30}]*Sin[Pi*z]*Sin[Pi*(-1+Sqrt[-3])/2*z]*Sin[Pi*(-1-Sqrt[-3])/2*z]
great
I am considering asking math.se to "Describe all ideals of k[x,y]/(xx,yyy)." I've described them all, but I'm a little worried I've missed the point. Anyone here want to describe them?
This is a deceptively nasty problem.
04:08
@mike: its very hard for me not to put \left( around his fractions
@Jack: There are some grammar problems, too. I think I'll just edit the entire thing, since I'm stuck in my attempt to find the exact expression wanted.
try splitting the bins up into three categories: 1 ball (A), 0 balls (B), and >=2 balls (C)...
@anon: That's what I'm doing. The >=2 bins case is the difficulty. But I just saw another problem I'm going to tackle. If you want to answer that one, go for it!
@jm: teehee, crystallography to the rescue. it's really neat studying finite subgroups of O(3) instead of "groups"
eigenvalues of group elements and such
@Mike: Note that if every bin in (C) has >=2 you can count the possible configurations by taking the number of balls available, subtracting 2 for every bin in C, and then acting like the leftover number is how many balls you put into #C bins with no restrictions.
(of course the no. of bins in C will have to be the index in a summation, I think)
04:44
@JM Again I say, he should change his name :)
"simplicity", that is.
 
3 hours later…
07:31
@Asaf: are you around?
For a short bit, yes.
What's up?
I'm wondering if one should do an (faq)-thing on Borel sets, and so on.
What's a (faq) thing?
You know, examples of sets that aren't G_\delta or F_\sigma, Lebesgue but not Borel, etc. These questions come up so often
They do?
I didn't vote for them. Except those I remember voting on, on which usually you answered.
07:33
Yep. At least once a week. And that's what I mean by faq
here's the most recent example (originally phrased in terms of Lebesgue measurability)
Oh yeah. There should be a couple of questions there. Including the famous sigma-algebra where Qiaochu answered the plain question, I introduced the hierarchy and Arturo just wrote another book.
I also need to badger someone to add elementary set theory in there.
?
elementary set theory?
Ah, to add that to the (faq)
I understood that the Arturo-Asaf-Qiaochu thing would be elementary set theory :D
Nah, that I could do for myself :P
Did you just vote to close that question?
What did you choose as duplicate?
The one which you already suggested as a dup.
I almost never suggest different duplicates.
07:39
But that was about Lebesgue but not Borel! Now it's not quite clear to me what the guy actually asks, I guess one should treat him to some Borel-hierarchy in...
The precise answer would be along the lines of: well, the Borel hierarchy can be described by transfinite induction on the level < \omega_1 by the operations you have. Just check that you get a sigma-algebra...
But I don't really understand what makes him ask about the unit square instead of the unit interval, so there seems to be some confusion.
Only god knows. Alas, he does not like to share much information.
I always thought that the Borel hierarchy is as long as it needs to be. :-)
I wonder how big is the Borel hierarchy in Gitik's model, where every limit ordinal is a countable union of smaller ordinals.
Probably not too easy to answer...
Let's see if Miller says anything about that.
There is no 12!! :-)
@Asaf: I misread the statement. I meant Prop 12 p. 12 on the ArXiV version.
(which is of course about something completely different)
I go to bed an you guys are chatting. I wake up and...
5
07:53
@Jonas: the crazier you are the less sleep you need :D
Good morning, btw.
Oh crap. I have a class in 15 minutes. I takes about 7 to get to the university.
I better jump to the shower and run away. See you guys later.
I like how you narrowed it down to 7. Usually traffic variation precludes any refined estimate.
I walk. I don't use any vehicle... :-)
Good morning.
08:08
Stupid hot water and their tantalizing feel... I over-showered and now I'm gonna be late!!!! runs away
Drat! The window didn't tell me that Sasha had answered the question before I posted.
Usually, a banner appears saying that an answer had been posted, but two were posted and no banner appeared. I would have posted earlier, but I was checking out numerical examples.
Stupid classroom. Buried in some basement...
how are you still chatting? are you on a phone?
@robjohn: I made the experience that if I have an editing window open in a tab and an answer is posted while I'm fooling around doing something else in another tab then the system does not notify me. I guess there's small bug in the script that triggers that notification only when the tab's active.
The tab was active.
08:23
@anon: Yes. It's an algebra class anyway... :-P
maybe if it goes inactive at any point the system bugs out or something
I guess my answer is probably the same as Sasha's, but I'll have to look at Sasha's answer to see.
He cites De Moivre's formula, which I have always called the Generalized Inclusion-Exclution Principle.
Hmm. There is no wifi in this class. Bye!
later
@AsafKaragila bye
08:36
What's happening here? The question seems somewhat "subjective and argumentative" to me but closing it as "not a real question" seems somewhat harsh, especially without any explanation and with a brand new user (member for 10 days).
08:51
@tb dunno. I guess on its own, what is being asked is vague or unanswerable, but your comment certainly is valid.
@JonasTeuwen Jonas, you sounded my feeling about this chat. that's why I was thinking that this chat exists only in my imagination
seems like Didier would burn Tim with his eyes only if he could: math.stackexchange.com/questions/78491/…
@robjo: good night
@Gortaur or whatever :-)
@tb good morning
Didier doesn't sugarcoat it, that's for sure
@Gortaur it is 2:05, so it is morning, technically.
@anon sugar coat what?
09:05
@robjo I think 2 am is too early to be morning
@anon Ah, never mind
@Gortaur okay
@robjohn never ever
@anon so you agree with Didier?
I have no idea, didn't even bother parsing the math there.
@anon ah, ok. sometimes 'to sugarcoat' means 'to exaggerate' in Russian
@anon A bit of gentleness is nice.
09:09
but that guy is quite careful about details. 4th link is a sort of control shot
Oh. I understand it to mean "to lighten it down" so as to not hurt someone's feelings.
@anon that is the way it is used in English mostly.
@anon I've got it now. then I agree
Being harsh has a way of coming back at you.
Karma at work.
sure
09:11
Perhaps Didier had a bad day.
if Tim was sentimental, the bad would be then transferred to Tim
@Gortaur sensitive or sentimental?
@robjohn both
and a bit about karma
and I like pedja's examples here: math.stackexchange.com/questions/78531/…
09:53
@tb agree. shall I do it or you?
@Gortaur: I can't, my browser doesn't let me use those popup windows, so if you can do it, please do.
@tb whic browser and OS do you use? if I may ask
@Gortaur Yes, that would be very good.
@Gortaur OS X, Firefox. For some reason, the popup windows pop up and disappear again immediately.
@Gortaur Am I mean if I think Didier's comment is quite funny?
@tb done. which version of FF?
10:07
@Gortaur: 7.0.1
@tb icic. if there any reasons for you not to use safari or chrome?
@JonasTeuwen I don't know if you're mean ) I hope, not. I don't find it quite funny, and sorry, I don't want to discuss it anymore
@Gortaur Safari is too unstable, I use Google for searches, but I try to avoid their other software.
(I didn't read the rest, just read a bit from where you mentioned my name)
@tb :-p if you're using Mac then maybe
10:10
Does Google give you the willies?
@JonasTeuwen our coffee machines give me willies
@JonasTeuwen yep. Scary, and I don't think of myself as being paranoid.
@Gortaur I can understand that if it is the same as the one we have.
@tb which paranoid thinks of himself as a paranoid, though )
<_<
>_>
etc.
10:13
@JonasTeuwen Douwe blah-blah-blah. I started drink only Wiener Melange from it. Reminds me of N.Wiener )
@JonasTeuwen what does this battle cry mean?
Is there no coffee bar at 3mE?
10:14
@Gortaur Everything except the hot water from the machine is horrible.
Norbert Wiener is the dead one right?
@JonasTeuwen at least one - yes
@JonasTeuwen sure. that's why I use to by Lipton-Lipton teaaaa
@tb Theo, they've started to removing it. nice
Wiener seems to have been quite a brilliant guy.
I wonder why someone would name himself after him...
@JonasTeuwen ok, if your surname is Wiener and you like the name Norbert, why not name your son in that way? Though you may not understand, your surname if different )
@Gortaur Yes, I've seen it, thanks PaÅ­lo, and sorry for the trouble
Then there is no problem of course :-).
10:20
@Gortaur That's just a big no-no
PaÅ­lo, thank you very much
@tb I would laugh and star it maybe if I know what does it mean, sorry. I'm sad and you're without a star
@Gortaur There's a gazillion of names to choose from, so pretty please, choose another one than the one of the famous person.
@tb haha )) Theo and you're the one who tells it to me ))
by the way, I named after a prophet (starting from I), so...
@Gortaur Want to have lunch at the Aula in an hour?
@JonasTeuwen sure
10:24
Good.
Okay, I think they are now all removed. It takes about three clicks for each message, and my internet connection is not that fast (or my computer has too many windows), thus it took some time. Next time please stop earlier :-) (@t.b, @Gortaur)
@PaÅ­loEbermann we will. thanks a lot
@PaÅ­loEbermann Thank you, and again sorry for the trouble :)
I'm off, have fun!
@Gortaur Well, that you definitely can't blame on me!
10:31
@tb the guy with my name was blaming, no way )
ah, ok: it starts with E in English
@Gortaur Ah, now I know who you are :)
@tb ) sometimes I think that this smile is a Cheshire Cat's smile. It's a pity that Mariano has already used that avatar - sometimes I use it too in other places. Like that Cat
@Gortaur Your name starts with an E in English?
@JonasTeuwen The prophet
@JonasTeuwen now, but my name in Russian is the same as the name of prophet in Russian
10:38
Oh.
So technically I'm a namesake of the actor who played Frodo. quite ironical
@Gortaur You're schizophrenic :)
Should rename yourself Sméagol, maybe?
2
@tb tell me just one reason to do it
@tb should I take it serous from a paranoic? )
the guy pretending to be Gortaur is a namesake of guy pretending to be Frodo. Diagram does not commute
oh no. the weirdest typo ((((
@Gortaur Oh, now I have figured out why it isn't so crowded :-). It's a class-free week!
@ah, indeed. I felt it especially in Aula
Yes he is :).
Obviously you need to be a little more subtle :D
What do you mean @tb?
Well, OP tried to get an estimate < 2^{-n} straight by starting with capping things at 2^n
Oh, right. That's quite a rough estimate.
10:54
@JonasTeuwen not for n=0 though
mathworld.wolfram.com/PrimeZetaFunction.html how can we say the Prime Zeta function is a generalization of Zeta function?
doesn't seem to be more general
@Gortaur generalization seems to be the wrong word: variant, analog, whatever.
I have no clue!
@Jonas: are you busy? I'm quite hungry
Yes, a bit, but we can go now if you want to.
I'm in about 7 minutes at the entrance of the Aula, is that okay, @Gortaur?
@JonasTeuwen sure, see you there
11:48
@Jonas: I liked your first question so what do you do besides chatting?
Hah.
Better than talking about the weather which seems to be typically Dutch.
@JonasTeuwen or football )
@JonasTeuwen everything seems to be so tasty )) thanks. I'll have to choose 2-3 from about 8
Yeah, there are nice courses, the PDE one is also given in Delft (different book though).
12:10
I appear to eventually expand Didier's comments it two consecutive questions ))
12:34
Interesting, I'm reading a paper that refers to another one to invoke a theorem, but the space they use is slightly different from the one they refer to. At least, I'm not able to prove they are equivalent. I hope they are 8-).
@JonasTeuwen the space in the paper or some kind of mathematical space?
The tent space in the paper.
13:15
@Gortaur : what is the difference between a space and a set ?
13:36
A space is often a linear space.
@RajeshD A set is more general.
@JonasTeuwen I would say that the space is no necessarily linear. it is rather a set with some structure, e.g. topological space
Right, true. It is a set with some structure, but I was referring to a linear space.
A space is just a place where things happen.
14:02
@AsafKaragila that is the free space I would say
14:38
@Srivatsan: hi, man
@Gortaur hey, Hi Gortaur
@Srivatsan shooting off-topic jokes? )
It's not a good sign if my day begins with a joke. =)
@Srivatsan icic
Yes, yes. Edited that comment.
I find it all the more amusing that the OP got the same -1 as the answer. Not any old negative result (like -42).
Ah finally, some on-topic comment in that post. (Thanks, robjohn.)
14:45
@Srivatsan 42 is even better universal constant (acc. to D. Adams) )
@Gortaur Yes, all my random numbers are either 42 or 57. =)
(So it wasn't coincidental that I picked 42...)
@Srivatsan what is 57 about?
[It's happens to be a prime number. that's all: en.wikipedia.org/wiki/57_(number).
Grrr, the link is bad and I don't know how to fix it. I just meant Grothendieck prime.
wth! I have an access to Notices. when I was 4-years-nerd I liked just staring at pictures in this journal
@Gortaur Hi If X is a topological space P' is set of all limit points of P then prove A' \cup B' = (A \cup B)' if A and B are subset of X.
14:58
@Ramana One direction is easy; which one?
@Srivatsan any direction works
No, I think you misunderstood. I am asking you a question (and guiding you to the solution). Remember that you need to prove (A union B)' subset of (A' union B'), and vice-versa.

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