Mathematics - 2013-02-19 (page 4 of 5)

Ilya

16:00

@robjohn is it the way you call tea?

Orange Harvester

chai..... ahaa...

Ilya

we say чай [chay] in Russian for the tea in general

Orange Harvester

yes, in india too.

as well as in china (though they say cha I suppose)

Charlie

@OrangeHarvester Jayesh!

Orange Harvester

@Charlie Yeah. :-)

Charlie

16:03

:D

Ethereal

@Charlie hi

how are you ?

Charlie

@Ethereal I'm good, and you?

Ethereal

i am okay .

it s been a long time since i ever typed so crappy grammar ..... thought i d try it now !!!!

Michael Greinecker

@Ilya Just treated myself to the first three volumes of Fremlin.

Ilya

@MichaelGreinecker treated doesn't mean "finished", does it?

Charlie

16:10

@Ethereal fo shizzle

Orange Harvester

@Ethereal ets nawt cuil, veri aard tuu undarshtand..... i vish u wont du it animoar

Ethereal

@OrangeHarvester not spellings !!!!!!!!!

Michael Greinecker

@Ilya No, a present to myself.

Ilya

@MichaelGreinecker icic. You mean, in a hardcover?

Michael Greinecker

@Ilya Yup.

Orange Harvester

16:11

@Ethereal knot swellings? they can be problematic, see a doctor.

Ethereal

@OrangeHarvester that grammar is pretty ok ,

Ilya

@MichaelGreinecker sounds cool! I would take a photo with them if I had'em

Michael Greinecker

@Ilya I will.

Orange Harvester

@Ethereal kreacher aaf habit am i, typing hard wrongly... extra exertion haf to do

Ilya

hm, at least the first vol. is 100 pages and does not look too scary :)

Ethereal

16:14

@OrangeHarvester that is a little too exaggerated . !!

Charlie

@OrangeHarvester someone may think you are speaking marathi

Orange Harvester

@Charlie not speak marathi with ethereal, not understand anything, hindi speak I to him..

Michael Greinecker

@Ilya I think volume 3(I+II) is where stuff gets wild. Quotienting out those damn null sets and working with the measure algebra alone...

Ilya

@MichaelGreinecker yeah, does not sound friendly :)

you tell me later who did you like the way it is written

user58512

I have a cold :(

Charlie

16:16

@OrangeHarvester geez

@user58512 oh no

Ilya

@MichaelGreinecker: it seems to me, he has GMT there, doesn't he?

Michael Greinecker

@Ilya GMT=?

Charlie

:8171262 what's up doc?

Ilya

@MichaelGreinecker geometric measure theory

Orange Harvester

@Charlie that did not ping me surprisingly

that's all folks

@user58512 How are you holding up?

Michael Greinecker

16:19

@Ilya GMT is apparently in volume IV(II), chapter 47

Ilya

@MichaelGreinecker where do you see the table of contents?

Charlie

@OrangeHarvester ;)

Michael Greinecker

@Ilya The electronic version.

Ilya

@MichaelGreinecker I have not been able to compile it :(

Michael Greinecker

@Ilya You can also get it on one of em Russian sites...

Ilya

16:22

:)

I'm not that bad, I use em Chinese ones :D

Charlie

@user58512 why you don't answer us?

robjohn

@Ilya Here, chai usually refers to a mid-eastern spiced tea. I know that one of my park friends is from Russia and he always tells me when I mention chai, that that just means tea to him.

Michael Greinecker

@Ilya Did not know there are Chinese ones.

Ilya

@robjohn icic

Michael Greinecker

@robjohn @Ilya en.wikipedia.org/wiki/Masala_chai

Ilya

16:25

@MichaelGreinecker discover something new every day :)

@MichaelGreinecker @robjohn: well, I usually prefer black teas with some spices. I was also drinking tea with milk when I was younger, but not anymore. Only with lemon sometimes

user58512

I want that

Ilya

@MichaelGreinecker: when I first read Chapter 7 of Bertsekas and Shreve, I was much surprised that such... practical guys wrote such a book

I knew their other books before

robjohn

@MichaelGreinecker that's pretty close

@Ilya I generally don't have milk, except for a chai mix that has dried milk in it already

Michael Greinecker

@Ilya I knew Shreve's finance book and that Bertsekas wrote lots of optimization books.

Ilya

@robjohn do you cook it by yourself, or you only need to add some water?

@MichaelGreinecker Shreve's finance is not very technical, neither is "Dynamic programming" Vol. 1,2 by Bertsekas

robjohn

16:31

@Ilya usually, it is just tea, spices, and honey

Ilya

@robjohn icic

robjohn

@Ilya Brew the spiced tea leaves, add honey :-)

Ilya

hm, that we also do

good when you're cold

robjohn

@Ilya Very good. If you refrigerate it, it is good cold for hot days.

Ilya

better also add milk and some rasberry jam

Michael Greinecker

16:32

gotta go briefly, bye folks

Ilya

bye!

robjohn

@Ilya jam in tea? Never considered trying that. I will take your word for it

@MichaelGreinecker have fun

Ilya

@robjohn I'm not kidding

@robjohn: until recent times, cold tea has not been popular in Russia

for obvious reasons

robjohn

@Ilya I didn't think you were. I just was not going to be trying that this morning.

Ilya

tea is ought to be drunken during long cold dark nights

@robjohn well, it depends on your taste, but helps smoothing one's throat when having a cold

robjohn

16:34

@Ilya We will have a fire tonight and I will make tea (chai and jasmiine teas) and have them while it rains outside.

@Ilya Honey and sometimes lemon work for me

Ilya

@robjohn sounds cool :)

Nimza

Hello! Who does know, what is a "vanishing Lagranian" or "zero Lagrangian" by definition in variational calculus? I know that it isn't $L \equiv 0$!

Ilya

maybe, it is vanishing out of compacts? would it make sense in your problem?

ah, Lagrangian

Nimza

@Ilya No, Ilya, here is a theorem without proof that any vanishing Lagrangian $L(x,z,p)$ has a form $S_{x}(z,p)+S_{z_i}(x,z)p^{i}$

Ilya

Lagrangian, you meant?

Nimza

16:38

@Ilya yep, oh La-La

Ilya

:D

why don't take it as a definition?

robjohn

@Nimza In the sense of a critical point?

@Nimza That looks like a function whose Lagrangian vanishes

Nimza

@robjohn hm, not sure, but it is true that if we solve problem of minimization $F(u) = \int_{a}^{b}L(x,u(x),u'(x)) \, dx \to \min$ then in neighborhood of optimum we have $F(u) = S(b,u(b)) - S(a,u(a))$, so there are no dependence on what happens inside $[a,b]$

user58512

> The reason it is difficult to convert results about low lying zeros to results about small primes is that the Explicit Formula, (mentioned in comments above) has the primes and zeros lying on opposite sides of a Fourier Transform. The Heisenberg Uncertainty Principle applies

where is the fourier transform?

Arkamis

I hate contact lenses.

>:(

robjohn

16:53

@Arkamis stop wearing them?

Arkamis

I lost my glasses, and my new ones aren't ready yet

Also, I'm pretty blind without any corrective lenses.

I'd have to set my screen fonts to "Old People" just to get any work done. A normal person could debug my code from Canada if I had to do that.

robjohn

@Ilya: you are on the second page

Charlie

@Arkamis oh damn it

Dominic Michaelis

hi

Charlie

Hi @dominic

Ilya

17:02

@robjohn interesting. Like #30?

user58512

hi

whats up

Nimza

What may mean notation $n$-$\mathop{\mathrm{graph}}{f}$? Is it usual for a set $\left\{ (x,f(x),f'(x),\ldots,f^{(n)}(x)) \mid x \in D(f) \right\}$? So that $0$-$\mathrm{graph}$ is a usual $\mathrm{graph}$

Dominic Michaelis

mh how to react if someone ignores your answer while commenting another one ?

user58512

ignore them

Charlie

@DominicMichaelis remove your answer mwahahaha

@DominicMichaelis or simply nevermind

Dominic Michaelis

17:13

my answer is right is't it [limits]math.stackexchange.com/questions/308158/…

robjohn

@Ilya Yeah, but more than 50% of your answers have been accepted!

Ilya

@robjohn aha

robjohn

@Ilya less than 1/3 of mine have been accepted

Charlie

@DominicMichaelis ... No comments , weird

robjohn

@Ilya Of course, looking at it another way, I have more answers accepted than you have answered ;-)

Ilya

17:20

:)

it either means that I visit MSE more rare, or that I cannot answer as much questions

Dominic Michaelis

@charlie and as i didn't got upvotes i thought it could be false , or something like that

Ilya

in my case, both statements are true :)

robjohn

@Ilya quality vs quantity ;-)

Charlie

@DominicMichaelis how do you know bn converges to zero?

Tim

@Ilya: I think your answers always have high quality. I appreicate that

Dominic Michaelis

17:22

@charlie no i know a_n converges to A

Charlie

@DominicMichaelis yes

Dominic Michaelis

and b_n -B converges to zero so b_n converges to B

Arkamis

Where's your B coming from?

Dominic Michaelis

@Ark a_n b_n converges to A \cdot B

it is given that a_n b_n converges

Charlie

@DominicMichaelis but do you a priori if bn converges?

Arkamis

17:26

You're defining a_nb_n -> AB, then, and you're defining B as the ratio of the limit of {a_n b_n} to the limit of {a_n}

And then you claim that {b_n} goes to B

?

Dominic Michaelis

@Arkamis no i know a_nb_n converges to let us say C

Charlie

Ok

Dominic Michaelis

since A is not zero i am allowed to write this one as A \cdot B where B is C/A

Arkamis

That's what I asked. Just clarifying

Dominic Michaelis

oh you are right thats misunterstandable

Tim

17:30

@MichaelGreinecker: Hello!

Dominic Michaelis

@robjohn better now ?

Charlie

@DominicMichaelis ;)

Dominic Michaelis

@rob fixed that one

now fine ?

or should i add a proof for the bound ?

i am so unsure cause it is homework

Michael Greinecker

17:49

@Tim Hello. Soory, was just reading stuff.

Tim

@MichaelGreinecker May I ask you a quick question about Ito isometry?

Michael Greinecker

@Tim I don't know much stochastic calculus, so I won't be of much use.

Tim

Thanks! I hope your moving well

Michael Greinecker

Thanx. me too.

robjohn

@DominicMichaelis: what I commented is what I see to be the correct way to use the triangle inequality

Dominic Michaelis

18:03

@robjohn thanks a lot :)

robjohn

@DominicMichaelis I removed my comment, which was too detailed for homework, and added a hint in another ansswer.

Dominic Michaelis

18:18

@AmWhy seems like we got the same results :D

i guess my answer is a bit to explicit or [geometric sequence]math.stackexchange.com/questions/308265/…

user58512

@DominicMichaelis, why do you do it that weird way?

Dominic Michaelis

what other way ?

over the series ?

@user58512 you don't have such a lot opinions what you are allowed to do, when you get such tasks

user58512

what?

Dominic Michaelis

what would be a less weird way ?

user58512

[0,r] is strictly contained in [0,1] since multiplication by r is a contraction mapping

Dominic Michaelis

18:33

well but that doesn't give you the limit

user58512

0r = 0 so limit is zero

Dominic Michaelis

you need that the diameter of your intervall is a 0 - sequence

user17753

Hey guys if I have a length 3 string with alphabet {A,B} it's easy to see that there's 2^3 possibilities. Though, what if I only care about the total count of A's or B's in the string? Then say AAB = BAA. I can see there's only 4 such outcomes, not sure what the general formula/approach is for the general case, though.

Dominic Michaelis

@user58512 i mean how do you know that it is contracting to 0

and not to something else

user58512

let n = log N/log r then r^n = N is arbitrarily large

@user17753, there's only one string with 2 a's and 1 b then?

Dominic Michaelis

18:36

this is a 4 -5 week freshmen task

in germany we have sequences a long time before functions like log

user17753

Right, another way to think about it is you list all the possibilities, then sort them alphabetically (So BAB would be ABB, ABA would be AAB, etc.), and remove duplicates.

user58512

what

you're counting the number of partitions of 3 into 2 parts?

3 = 1 + 2

user17753

I don't know the nomenclature, trying to figure out what I need to learn to solve that kind of general problem.

user58512

just write down the answer

pourjour

how can I find the value of L

supposing r = 440 $\Omega$

and there is the same current in all the circuit

user17753

18:43

Well I wrote out by hand AAA, AAB, ABB, ABA, BAA, BAB, BBA, BBB which is 2^3, then I can see it's either 3A 0B, 3B 0A, 2A 1B, or 1A 2B. Which is four ways.

Just trying to determine what is needed if I generalize this to say an alphabet of k elements and string of n length.

user58512

oh you care about order and allow zeros

user17753

Just care about how many A's or B's are in the strings.

So AAB and BAA become equivalent.

So it removes some from the k^n possiblities

user58512

I see

user17753

In this small case, it reduces them by half

I'm sure this type of problem has a name or something, but I don't know what it is.

user58512

this is a difficult problem

pourjour

18:48

and the frequency of the generator is $f=150 Hz$

heelp

user17753

Well I'll just make a question out of it thanks

pourjour

19:05

any help

user19161

@anon How is your headache?

Charlie

@pourjour what is L?

pourjour

19:20

@Charlie the inductance

user58512

I cant think properly beacue I hahve a cold :(

what should I Do

Arkamis

19:46

sleep

user58512

its to early

Arkamis

Not if you're sick.

user58512

20:20

i want to answer a question on the site but the last two i tried were too tough

Dominic Michaelis

same with me :D

user58512

sup @DominicMichaelis

I ujst solved one but someone else posted what I was going to write..

5

Dominic Michaelis

g

Since when $\mathbb{C}$ is a $\mathbb{R}$ vectorspace (I don't mean the isomorphism to $\mathbb{R}^2$

user58512

20:39

thats when

Dominic Michaelis

sry for my english

user19161

@DominicMichaelis In most books I have seen, it is written as two words: vector space. Some authors call it linear space.

Dominic Michaelis

@Jacob in every book i have written it is Vektorraum :D

user19161

@DominicMichaelis Haha, how many books have you written?

Dominic Michaelis

oh sry seen :D

i just wrote some scripts

user19161

20:51

@user58512 How is your course coming along?

user58512

i really have no idea

I think I have a chance

user19161

Yes, there can be miracles when you believe.

user58512

i hope youre right

only a few more weeks of class then i get down to revision

how are you doing

anon

21:12

@JacobBlack bleh

Dominic Michaelis

21:24

how difficult msut a question be to be posted on math overflow ?

David K.

Math overflow is for questions that no one really knows the answer to, if an answer even exists.

anon

minimal conditions: graduate level, conjectural, or open

@DavidK. that doesn't seem like an accurate characterization

Dominic Michaelis

so this one is to easy ? []math.stackexchange.com/questions/308445/…

anon

@DominicMichaelis yes, that would not be at the MO level

Arkamis

The only response you would get at MO is "start listening to your topology lectures"... especially considering how many MO posters are faculty.

David K.

21:30

@anon Yeah I guess you're mostly right. 'graduate level' can be a bit ambiguous though. Is research being conducted by a graduate student in preparation for a dissertation 'graduate level'? Or is a question from a graduate level text for a required graduate level course a 'graduate level' question?

Dominic Michaelis

well it's my third semester didn't got a chance listening to topology

anon

nitpickiness on an already ad hoc demarcation seems pointless

Dominic Michaelis

sry my english is bad

David K.

@anon I agree. Unfortunately the vagueness of this line is what keeps me off of MO for the mostpart.

That and 'I got the dumb' when it comes to math...

Arkamis

Ah, you mean you haven't taken a topology course... not that you are taking one, but don't pay attention ;)

Dominic Michaelis

21:34

@arkamis yes that is what i mean

mick

22:10

Hi folks

Dominic Michaelis

hi

mick

@DominicMichaelis hi :)

@DavidK. wow

David K.

@mick Yes?

mick

well it sounds to be as usefull as asking : Is the RH already solved and give me details of of the best attempts so far (subjective!) I am not able to understand anyway.

also , there are sufficient open problems at MSE. and Some MO have got answers.

Dominic Michaelis

RH= riemann hypothesis ?

mick

22:19

yes

RH means RH :)

David K.

Yes, but I seriously doubt an answer existed, when the question was asked, for ALL the questions that have now been answered on MO. I was merely alluding to the fact that MO is more for 'research level' questions.

mick

How much reputation here is needed before you switch to MO ?

Dominic Michaelis

10^10 :D

David K.

$\lim_{N\to\infty}N!-1$

mick

why not a googolplex ?

Im pretty sure that 50k rep at MSE must be at least 50 rep at MO or Ill eat my hat :)µ

@DavidK. Is that countable or uncountable ? ordinal or cardinal ? ZFC or Quine ? xD

For instance Robert Israel is an asso prof. He is on MSE and has above 70k rep. Surely he will get some rep on MO or maybe already has.

Khromonkey

22:26

hi guys

mick

@Khromonkey Hi!

say guys how does community wiki work ? Do they not show up in the question list ? I do not understand how and why that stuff works ?

Dominic Michaelis

i only know one guy on mathoverflwo

on MSE he has 10 k reputation and on MO 27k repu

mick

SO MO is easier :p

@DominicMichaelis

Dominic Michaelis

seems like

Khromonkey

community wiki means you don't get reputation

mick

22:29

@MarianoSuárez-Alvarez hi

Mariano Suárez-Alvarez

hello

mick

@Khromonkey But what is it used for ?

Khromonkey

for questions that just ask for big lists of stuff

and other things I don't know

mick

@Khromonkey I do not agree. I think it is given to specialized subjects with lesser general intrest. As an example I got community wikid for tetration questions.

Khromonkey

You do not agree with what?

Big list questions almost always are community wiki

mick

22:32

But my question is : is community wiki different for search ? Can you do a community wiki search ? is it related to wiki ? Can you still get answers later on ?

ok thats many questions

Khromonkey

I know that you can still get answers later on

and community wiki is not different for search

mick

thats good :)

I wonder about plot or table requests.

is that acceptable as a question here ?

David K.

What do you mean, plot or table requests?

mick

For instance a list of the first 1000 lucky primes. And a plot of that list.

Dominic Michaelis

what is a lucky prime ?

mick

22:38

lucky primes = primes that are also lucky numbers

David K.

what are lucky numbers?

Oh I see.

mick

Lucky number

In number theory, a lucky number is a natural number in a set which is generated by a "sieve" similar to the Sieve of Eratosthenes that generates the primes. Begin with a list of integers starting with 1: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, Every second number (all even numbers) is eliminated, leaving only the odd integers: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, The second term in this sequence is 3. Every third number which remains in the list is eliminated: 1, 3, 7, 9, ...

David K.

Well, I was going to recommend (www.wolframalpha.com). But it doesn't seem to know about lucky numbers.

Dominic Michaelis

here you go oeis.org/A031157/graph

David K.

How do you make a link in here.

@DominicMichaelis Hey cool!

Khromonkey

22:42

How can I get someone to answer this? math.stackexchange.com/questions/178122/proof-about-factorials

mick

Yeah well I would ask things that are not easy to program in standard math programs obviously. and not on the oeis pages.

@DominicMichaelis It was just an example ! I want to ask similar questions here because I cant program it and its not on oeis.

Dominic Michaelis

mh as the questions can be emmigrated i would try it

mick

emmigrated ? list requests are emmigrated ? Im confused.

Dominic Michaelis

sry i mean for example it could be solved on the mathematica stack exchange

or what programm you are using

if the questions doesn't fit in MSE

mick

@Khromonkey I starred it , plz star back :)

Khromonkey

22:46

@mick does starring help?

besides I don't know which is your question

mick

@Khromonkey I think so. it indicated popularity and increases your reputation.

Khromonkey

you didnt provide link

and star doesn't increase rep

mick

@Khromonkey Just star a random one of me. :)

@Khromonkey It does.

Dominic Michaelis

it's hard to get 10 stars on a single message is it ?

mick

not on message on the question !

i starred his question

and yes that is hard too

and it gives rep

Khromonkey

22:49

only upvotes, downvotes and accepting a question gets you points

mick

for the receiver

Khromonkey

and does anyone know how I can get my question ansewred

?

Dominic Michaelis

your answer answered ?

mick

@Khromonkey sure ?

Khromonkey

Can I delete answers on my question?

mick

22:49

@Khromonkey that is imho not a good idea

ppl will downvote the bad answers anyways

Khromonkey

Why not? They don't answer the question

mick

downvoting lowers your own rep too

-2 i think

Khromonkey

I want to delete not downvote

Dominic Michaelis

-2 to the other -1 to yours

mick

anyway I think i will post a list request that will very likely become community wiki !

Imho math software is mainly for calculus ...

Dominic Michaelis

22:53

for what else ?

Khromonkey

@MarianoSuárez-Alvarez Is it possible to delete the answers to this question? math.stackexchange.com/questions/178122/proof-about-factorials they are wrong

Dominic Michaelis

@khromonkey for sure if you get enough reputation you can start a delete vote

Mariano Suárez-Alvarez

We do not delete wrong answers: downvote them, and/or add a comment saying the answer is wrong and explaining why.

Even a wrong aswer, properly accompaned by an explanation, is helpful.

mick

@MarianoSuárez-Alvarez agreed

Dominic Michaelis

oh sry

a delete request can'T be made

mick

22:55

@DominicMichaelis tetration , fractals , selfreferential dynamical systems ...

@DominicMichaelis for a question I believe it can.

Dominic Michaelis

yeah with 10 k reputation

as the moderator tools

Khromonkey

@MarianoSuárez-Alvarez but wrong answers should be corrected

mick

yes

Mariano Suárez-Alvarez

Correct them in a comment

mick

@Khromonkey You can request that in the comments , but most k rep poster will do it automatically

Mariano Suárez-Alvarez

22:56

mods are not referees

I do not vouch for the correctness of anything

even my own answers

mick

@MarianoSuárez-Alvarez intresting

Khromonkey

@MarianoSuárez-Alvarez I can't get that person to answer

mick

@Khromonkey he is busy then.

Mariano Suárez-Alvarez

add a comment then explaining why the answer is wrong

mick

be patient

Mariano Suárez-Alvarez

22:58

I cannot see what the problem is, really

Khromonkey

did you look at the question?

Mariano Suárez-Alvarez

no, because it is completely independent of the question

I would have answered the same for any question

Khromonkey

The answerer accepts it's wrong

mick

@MarianoSuárez-Alvarez are list request acceptable here at MSE ? Or will it get closed or downvoted ?

Mariano Suárez-Alvarez

it depends on the question

Khromonkey

22:59

depends on the list

mick

@Khromonkey then he will change it soon probably. problem solved :)

Mariano Suárez-Alvarez

I tend to dislike them

Transcript for

$Mathematics$ Mathematics