Mathematics - 2011-10-25 (page 2 of 2)

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3:03 PM

@Gortaur going to contemplate a little further, if I get around to it I'll post it on MSE. Thanks so far! See you around

@mafutrct I was of small help I think, but you're welcome

@JM out of manna to rain on people?

@robjohn From Dust?

?

they changed the title apparently

|genre = God game, sandbox |modes = Single-player |platforms = Microsoft Windows, Xbox Live Arcade, Playstation Network |ratings = |media = Download, cloud computing }} From Dust is a video game, designed by Eric Chahi and developed by Ubisoft Montpellier. Ubisoft described it as a 'spiritual heir' to Populous, a British game developed by Peter Molyneux and Bullfrog Productions in 1989. The PC version was originally scheduled to be released at the same time but was delayed to August 17 due to undisclosed reasons. From Dust is distributed online via Steam, OnLive, GamersGate...

3:05 PM

But, but... I answer because its fun! That they're actually helpful is a happy coincidence...

(Okay, not entirely true. But I'm missing the sort of questions I like and are yet unanswered...)

how do you find time, I'm curious

Who, me?

My son probably knows a lot about From Dust, but I don't game online much.

I've spent almost all the day reading the book and don't have just a 30 min to focus on a small problem

@robjohn is it online??

@JM yes

@Gortaur I don't know. It sounded as if it were, but I didn't read more than the part of the page that showed on chat.

3:09 PM

@robjohn the only online game I played was World of Tanks, there I've got Koenig Tiger, played a bit with this lovely monster and stopped playing: to go further I either have to spent too much of the time or to start wasting my real money on this game

it was for free, but if you pay you have +50% of all the stuff. no way.

That is why I don't start playing games on the computer. Board games with people don't tend to be such a time-sink.

@robjohn sometimes I play in NFS: hot pursuit just to relax my mind

because grand piano is not always available unfortunately (

@Gortaur: Hmm, find time for math? Just the same way I find time for my other hobbies...

@JM: no, I mean that sometimes it seems that you're doing it without any break ) though maybe it's because it's me who slow doing this stuff

What do you mean? I have an actual job, too... :)

3:17 PM

@JM I don't have any doubts about it. I wonder how do you manage to work so much on MSE the same time working on your job

Also, I do take breaks from math.SE . Sometimes as long as a few months.

@Gortaur: believe it or not, math.SE is one way I unwind.

jm: your picture for the pole is good

unwind=relax?

@Jack: I had the picture prepared, but Sasha already wrote an answer... :D

@Gortaur: yes indeed.

@JM ok, then it's my lack of knowledge

3:20 PM

After a grueling job, it's fun to either a. make quips or b. solve a few puzzles...

math.SE fills that particular void for me

However, when I'm too baked to even think about math, then I watch TV...

Holy everloving... where are all these people coming from? Look at the number of views!

3:37 PM

if only they came with questions about the structure of finite groups

2

Q: Involution centralizer does not determine the group

Is there a finite group which is contained in infinitely many core-free finite groups as the centralizer of a central involution? The Brauer–Fowler results show that if a finite group has no non-identity normal subgroups of odd order (so is core-free), then its order is bounded by a function...

one thing I like about symmetry and graph theory is that if I have question there, I just ask my 150 students it, and one or two at least find me an answer by the end of class

Heh. It requires a some straining of the imagination, though. :)

Well, two grateful customers today! I guess this day isn't so bad after all...

3:57 PM

@JM On MSE or IRL?

Well, MSE. :)

Got your priorities straight at least :-)

)

sometimes I think that my posts like ')' took too much space vertical compare to their horizontal size

@rob: In RL, no customers; just technicians. :) I don't have the necessary charm to face customers... :D

1

Q: complete metric space

Prove or disprove: $(A_i)_{i=1}^\infty$ are closed subsets in a complete metric space. Assume that there is an open ball in the $\bigcup\limits_{i=1}^\infty A_i$ , so exists $k$ s.t $A_k$ contains an open ball as well. Thank you!

homework metric-spaces

I wonder why the [general-topology] tag was deleted. quite topological I think

4:05 PM

You could put it back, you know... along with a comment explaining why it should be there.

could I? you mean not rollback but edit one more time?

Well, you have the rep for the task...

aha. lame start of the week on MSE for me

Also, Chris looks like a reasonable guy; if you have a good reason, he shouldn't have trouble with you restoring the tag.

@JM looks like

4:11 PM

I've only seen his activity, but I haven't actually talked to him (unlike, say, with you); hence "looks like".

@JM I just agreed with you |

and put my supersmart answer 1 minute before your comment ) while you were editing I guess

Well I wasn't sure! I don't know him as much as I know you.

If I still had votes I'd vote your answer up...

If I have weak convergence in L^p (1 < p < infty), what are some conditions that would allow me to extract a (sub)sequence that converges pointwise a.e.?

@JM 2 is more then enough for such answer ) but you can upvote it tomorrow ;D

maybe I shouldn't complain: +95 today for doing nothing for 20 minutes overall, not so bad

see you all tomorrow

See you!

2 hours later…

6:25 PM

Would it be inappropriate to write on homework assignment you've been correcting "Well done!" if they scored less than 30%?

6:43 PM

@JonasTeuwen For the United States: I recommend very conservative grading. Indicate clearly what they've done wrong and what they've done right. Don't encourage bad behavior by joking about it, and don't encourage complaints by mocking them. Remind them about office hours and any on-campus tutoring services.

I think it is less formal here (The Netherlands).

But I won't do it, but I was tempted to do that sometimes...

But thanks for the advice @JackSchmidt.

no problem. i figured the direction of the advice would be close, but the magnitude would probably be wrong.

1 hour later…

7:59 PM

"Well done" and less than 30% might be applied to cooking meat and the fat content thereof; however, I prefer less heat and more meat. As for homework, not so much. :-)

1 hour later…

9:18 PM

It can be slightly frustrating that easier questions get much more votes. But, there are people that spend a lot more time than me on long (and complicated) posts and still don't get many votes.

@JonasTeuwen I agree. Look at some of my answers. :-)

I will collect a sampling that display this tendency.

Yes :).

Of course, in so doing, I may get more votes ;-)

Why do we actually like those votes so much? :).

Perhaps this tendency reflects a tendency of users on the site to vote on what they understand.

9:21 PM

@karmic_mishap that is true. However, they should all just understand that my answers are correct :-D

Of course, all of this means that those of us who do understand a particular long and complicated post should upvote it!

Or we could just automatically upvote all of robjohn's answers. ;)-

Sheesh, that question is open again :|

I am beginning to think that I serve as a warning to others

@MikeSpivey I commented on one of your fine answers regarding a binomial sum \binom{n}{k} 2^{k^2}

@Asaf: What question?

9:23 PM

@Mike: That "Inherently discrete concepts" thing. He even added tags and a bounty.

I often just do +1 on very long posts that look good before I have even studied them completely...

@robjohn: I saw it. Thanks.

@MikeSpivey this one

@Mike sorry, I have trouble with the links.

@JonasTeuwen Yeah, like "Good for you for sitting so long..." I get those a lot when I write incredibly long posts about the axiom of choice :D

I thought Asaf was asking which question I was talking about

9:27 PM

@karmic_mishap If that was true then some of my posts would not have gone past 3-4 votes. Incidentally, some of those got beyond 20.

And to display my craziness, I kept replying to the same message, expecting a different result.

@rob: I did the same thing over and over again and my sound came back. So it might not be insane to do that :D

@AsafKaragila I don't have such a flagship yet.

Hmmm @AsafKaragila, I guess that means that there may be a fair amount of what @JonasTeuwen was referring to.

@Asaf: I see. Yikes, especially that the question would elicit that comment from Arturo (which I will refrain from reposting here).

@JonasTeuwen I do that, too, sometimes - particularly if the answerer is someone whom I have had reason to trust in the past.

9:30 PM

@karmic_mishap Yes, we all do that. When you see a post that you feel is trustworthy, you can vote it. Sometimes just long votes that are not complete junk would be subjected to several upvotes. Not always, I'd guess it depends on the user as well.

I wonder if someone already wrote a script that enables me to have this channel in irssi.

It goes to the Vote Early, Vote Often ideology.

What is the maximum number of votes you can give in a day?

30 votes. 40 if you spend on questions more often than on answers.

@Jonas: 40

9:31 PM

Oh, now it's just 40? I recall you have to have at least 10 votes on questions there.

@Asaf: Maybe I'm wrong.

@JonasTeuwen the closest thing I've seen so far is this project that's still being worked on: github.com/ghewgill/soirc

@Asaf: It looks like you're right: "A maximum of 40 votes can be cast per user per day, however, to reach the maximum you must vote on at least 10 questions." stackoverflow.com/faq#reputation

@karmicmishap Looks far from finished.

@rob: How was Griffith Observatory?

9:37 PM

It was a very nice lecture about the supermassive black hole at the center of the Milky Way.

Awesome. Does it suck hard?

The person speaking was very knowledgeable.

@AsafKaragila extremely.

@Asaf: I laughed hard enough at that that I started choking.

@MikeSpivey The Observatory is usually closed on Mondays, but they have a series of lectures for the members of their support group.

@robjohn Cool.

9:41 PM

Anyone like noncomm rings? I think this question may have two "wrong" answers, but my only answer is pretty round-a-bout.

2

Q: every $R$-module is free $\Rightarrow$ $R$ is a division ring

From Grillet's Abstract Algebra, section VIII.5. I'm trying to solve exercise 9. I suspect it should be formulated: Let $R$ be a unital ring. Then $R$ is a division ring $\Leftrightarrow$ every unital left $R$-module is free. Attempt of proof: $(\Rightarrow)$: theorem 5.2. $(\Leftarrow)...

linear-algebra abstract-algebra modules

@MikeSpivey Well, then it is a good thing that I know the Heimlich maneuver!

Is that an alien using a wireless headset?

i suspect a ninja dj

aha.

@AsafKaragila If you can perform the Heimlich maneuver all the way from Israel to the U.S. then I am mightily impressed.

2

9:43 PM

if you cover one eye, it becomes a pirate dj

I have one vote left for today. What is a topic that deserves my final vote?

If no one else is going to speak up, you can look at this.

@anon: hey, I couldn't get those notes to solve my problem. the graphs i've checked have girth 3, and the left hand side is about 4

It's good for a laugh

@Jack: I didn't mean to sound like I knew the answer! I have no idea.

9:47 PM

graphs with girth?

cool. I think i'm going to make some string and bead models of them tonight

@robjohn That was a good one.

@J.M.: You probably saw this question from a couple of days ago. Did you catch that I used basically the same argument as on that interesting asymptotics question from last month?

This interesting question, I mean.

@MikeSpivey It's a magic trick that I'd learnt.

@AsafKaragila I bow to your magic powers.

9:51 PM

@MikeSpivey You mean? I thought only robjohn is mean.

@MikeSpivey No need to bow. I charge 50 bucks :-)

That's like 2 euros.

@AsafKaragila He's mean squared, right? I'm not even in the same league!

@JonasTeuwen Is the exchange rate that bad now?

No, I actually have no idea.

@MikeSpivey Yeah, I think he is also the root of all mean. So he's the squared root of himself... so he's either 0 or 1

The Euro isn't doing very well either :).

9:54 PM

@JonasTeuwen Google says it's more like 36 Euros.

Sounds more like it.

Hey Mike. Neat bits! I'll upvote in two hours (and I still owe Hans an upvote).

@JM @Thanks!

Hi @JM

@J.M.: Do you ever run out of upvotes for a day catching up on all the voting you would have done the day before had you not run out of upvotes then? :)

9:57 PM

Guten morgen, König. :)

Hi @JM.

@Mike... exactly the situation I have. (If I didn't know any better, you'd have scared the daylights out of me.)

Hi Jonas!

@J.M.: And, on a serious note, Thank You for all the voting you do. I'd probably have half the votes I do in some of the tags like optimization and LP if it weren't for you.

I have reached my voting limit for the first time today!

Congratulations.

10:00 PM

@Mike: Lucky for you, I like those subjects... :)

@JM Yep! As I said, thanks! :)

(Those guys asking about euro-dollar conversions: xe.com)

@Mike: You said something about writing a paper based on a question here. What is it about? (Did I ask that already? I forget.)

My 8 most popular tags are all involving analysis.

@Asaf: check Mike's blog.

10:01 PM

@Asaf: What J.M. said. A couple of posts down, I think.

This?

@Jonas: Yep!

@AsafKaragila It is also mentioned here

@AsafKaragila The Lah Numbers link

Yeah, I figured it out :-) Thanks.

It's more of an expository paper than a research paper, although I think the fact that the Lah numbers show up as the coefficients in the derivatives of e^(1/x) is actually new.

I keep thinking that there's a slick way to answer this question using complex variables, but I can't seem to make it work. Srivatsan's answers are nice, though.

10:09 PM

Well, I have filled my quota of Sigmas for the week :P

22! Well, that product does collapse neatly...

Say, from an ultrafinitistic point of view... the factorial is a bit problematic no?

I mean, after something like 40-50 there is no such number anymore, as 50!

@Asaf: I know not that of which you speak.

50! is \approx 3e64. Yeah, quite big, but I don't know what finitists consider as "too big".

Woohoo, the Vox Populi badge!

10:17 PM

@JM Not finitists, but ultrafinitists. I think that they would all agree that googleplex is moot.

So their fields are not closed under addition? What?

Sorry, I tend to lump them... :D anyway, there's around 10^83 particles in the universe, so 3e64 is still a bit short.

I see.

So 50! exists :D

What about 100!?

9e157 is sort of high... ;)

O.K., so I just spent some time looking up "ultrafinitism," which eventually lead me to this interesting article/rant‌.

10:23 PM

Well, it's DZ... why won't it be a rant? :)

Oh that claim that R is not "true mathematics" but rather an approximation of a part of the rationals?

@robjohn Hi

The entire perspective, really.

@RamanaVenkata how's it going?

Fine

@robjohn I have one question to ask

10:26 PM

@RamanaVenkata go ahead :-)

I remember when I was a young teenager arguing with some English-speaking religious (Islamic) scholar on his blog over whether or not the universe was discrete or continuous. Fun times.

@MikeSpivey Interesting rant...

@anon: You gave him stuff on quanta, no? How'd he take it?

I can't remember much, I was like 13 or 14.

Can arbitrary intersection of infinite sets be infinite? I think its false. Am I right?

10:28 PM

What is a "Naked Brain" human? According to Zeilberg I am one.

@RamanaVenkata It depends on what you mean by arbitrary intersections

@J.M. My contention was that continuous models make more sense but theoretically the universe could be discrete, and his contention was that logic dictates the universe is discrete definitively. (And I don't mean "quantized.")

You can have an uncountable intersection of sets still have full measure.

A_x=R^2\{0,x} for x in R

The intersection of all the A_x is just R^2(x-axis)

@anon: Okay. On the other hand, I don't understand how you're drawing the line between "discrete" and "quantized" though...

@robjohn I am using arbitrary in the sense that I can use any possible combination of Infinite sets for intersection.

10:31 PM

(but I do agree continuous models work and are appropriate most of the time)

@RamanaVenkata did you see the A_x I wrote above? Does that violate your setup in some way?

@J.M. quantum mechanics doesn't say everything exists on a grid with finite differences, it just says certain global quantities of a system are discrete, if I understand correctly.

Ah, alright then. :)

@robjohn Yeah

(On the other hand, note the flurry of attempts to quantize everything in the recent years... ;) )

Put another way: I've seen the theory, but I remain unsure about there being a graviton, for instance...

10:39 PM

Wait until they start stringin'

That's another kettle of fish. :)

Are you out of barrels?

Actually, I'm fresh out of cans of worms...

...so I settled for a kettle of fish.

@Jack: That Möbius question is nice! Any reason why you didn't add a topology tag?

You settle for a kettle?

that reminds me. Yau's the shape of inner space is online for free: stringworld.ru/files/…. Not sure if it's legal or not. It's one of the top search results for the book's name (so you find it without trying) but it happens to be on a .ru server, and if places like library.nu or bib.tiera.ru are any indication it's pirated...

10:44 PM

@Asaf: Why not? I have the mettle...

@anon: I'll take a(n objective) look and try to forget that Yau shabbily treated Perelman for the time being...

I was not aware of any scuffle between them. I shall have a look and see...

@JM Sounds like a troublesome fettle.

"A New Kind of Hammer" - does he speaks of Mjolnir?

Mjolnir ain't new... it's older than dirt!

Older than time, too.

Now that I think about it, I don't think I've ever seen Bill Thurston comment on his conjecture being dispatched anywhere...

10:53 PM

Good night, guys.

Good night, Jonas!

Bill Thor-stone??

That's just Bill Mjolnir.

My, you're feeling punny today.

What have you been drinking?

I'm all puckered out from lack of sleep.

I am not tired, though.

Mostly hungry.

I see at least two tags here that aren't quite comfortable where they are...

10:59 PM

@JM: I see four. And the bounty is ridiculous. It requires a complete answer.

Given the tendency to generalize everything... I'm not quite sure there'll be a better answer than Srivatsan's comment.

Me neither.

Bunchawimps :-)

They were complaining about how complicated the numbers got. The hardest thing to do was square 8.5.

I got what you got (I was running through the calculations when your answer popped up.) I don't know what's their definition of "simple"...

I like DJC's comment

he had answered that linear scaling was lost. I commented on his answer that that was for norms, not metrics.

The OP accepted his answer.

11:10 PM

Well, Zev nuked DJC's answer per DJC's request...

Yes, I didn't see his comment until it was gone.

DJC's reply to your comment: "You're absolutely correct. I'll delete the post if the OP designates another answer as correct."

Did Zev nuke it or did DJC delete it?

DJC asked how to delete an accepted answer on meta, which I appreciated. I had an old (> 1 year) incorrect accepted answer that I've been wanting to get rid of for a long time. I didn't realize that a mod could delete it for me.

It was Zev. OP hasn't come back to undo his check.

11:12 PM

Oh, Zev was not the OP. Okay.

Oh man. I just realized.

I am taking two courses this semester...

@robjohn: You can't delete your own answer if it has been accepted.

Commutative and homological algebra; and Basic Concepts in Topology and Geometry.

For the love of chaos, I wish there were more set theory courses here...

@MikeSpivey Thanks. I didn't know that. I guess that is why all the talk about the mod deleting things :-)

Did Zev unaccept the answer as well, or is it still accepted?

Still accepted.

11:15 PM

I don't think mods can undo accepts of users.

Sorry I have to ask these things; I am still below 10K :-)

I can't look at deleted answers.

@robjohn I found out the hard way. I posted a wrong answer, the OP accepted it, and then somebody else pointed out what I had done wrong. I tried to delete the answer but was unable to. The OP, meanwhile, never came back to the site.

So can the OP unaccept a deleted answer? If the mod can't unaccept it, that acceptance is in limbo.

@robjohn At the rate you're going, though, it shouldn't be much longer to 10K.

Agreed. Like I said, if you only joined earlier, you'd be 10k at this point... :)

11:17 PM

@rob: See DJC's question on meta.

I think I'll go to sleep early today... 1:30 :-)

That is where the "chaos is fun" happened :-)

@AsafKaragila for shame!

Chaos is fun!

@robjohn I couldn't function today with only 4 hours of sleep for three nights straight :\

@AsafKaragila Piker! :-p

@rob: Eh let him sleep. It'll be a challenge for us to deal with the resulting silence... ;)

11:22 PM

@J.M.: How are the hypergeometric edits coming? I pretty much rewrote all of the Faa di Bruno section, but I think I'm converging on being done with my part.

And I had a visitor from TAU today, and we didn't do any actual work. Just came to the conclusion that my idea from the last time we met was not good in its naive form.

So it's back to the drawing board :\

@AsafKaragila sleep on it. It will come to you in a dream.

that you will forget upon waking :-p

@Mike: Since the ref was begging for some historical background (if I read what he said correctly), I'm still digging up stuff on Kummer. I am also trying to see if I could squeeze in the Vandermonde approach to proving Kummer's transformation...

@robjohn If only my dreams were that simple :\

(Remember when we thought it might make the paper too long?)

11:24 PM

Well, so long folks.

See you, Asaf.

Catch you later, Asaf.

@J.M.: Yes, I do. That's been part of my problem with several of the edits. How to provide more background info on the techniques without detracting from the main line of the argument and making the paper too long? That's a large part of the reason why I rewrote the Faa di Bruno section. It doesn't use Bell polynomials anymore, but the argument is much more (IMO) transparent.

But you at least left a mention that the business can be done with Bell polynomials, right?

@JM Only a mention. I'm actually using a different version of Faa di Bruno's formula now. Hopefully I can finish up my part of the edits tomorrow. If I do, I'll send you what I've got by email.

With the new version I actually prove Faa di Bruno's formula.

Sounds great!

11:32 PM

Hopefully that will make the ref happy that we aren't just pulling a new technique out of a magic hat.

And I'm checking out, too. Time (once again) to go pick up the kids. Catch you folks later...

See you, Mike!

Missed Mike while reading some answers.

I should probably go, too. I have some errands to run before walking the dog.

I still have an unread answer backlog and a bunch of IOUs. Two for you, if I've kept track right.

11:49 PM

maybe SE should develop a voting cache :)

I think so, too. There have been days where I didn't quite get to use up my votes...

Off for now. Later.

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