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00:21
@EnjoysMath @Charlie @MarioCarneiro @robjohn @r9m @ArthurFischer
Why am I being pung?
oh you were pung
just seeing who is here :)
are you a graduate student?
@Chris'ssis I have summed the 2 variable version using series manipulation and I get $$\frac{\pi^6}{2835}$$
which is $\zeta(6)/3$
I cant figure it out
00:36
@TomCruise can't figure what out?
the terroir
5 years is the minimum before opening a Bordeaux
20 is about perfect
3 to 7 years for a pinot
01:07
jmilne.org/math/Books/ectext5.pdf why is the statement at the top of page 68 true?
nvm got it
my troubles always stem from my laziness
01:57
@nigelvr I'm the same.
 
2 hours later…
r9m
r9m
04:06
what is the difference between this and this, the later looks infinitely well recieved >:( ...
sometimes I feel like people are too jumpy to mark questions as off topic ... >8( .. I'm pissed off ... (growls) .. I was typing a cute little solution :| dang !!! :'(
04:29
if you find the solution to your question on math se and you can't delete it but you have answers, what do you do?
Anyone have any idea how to even begin tackling a question like this:
1
Q: Interesting Summation Congruence

ruadanLet $5\mid a$, $\gcd(a,b)=1$, and $b\equiv 2\bmod 5$. How can one show that $\sum_{k=1}^{a}k\lfloor\frac{kb}{a}\rfloor\equiv 2\bmod 5$?

04:57
0
Q: Question on Moment of inertia about center of mass of a smooth plane curve.

Rajesh DThis question is in continuation to this and motivated to answer this question. If I have an answer to it, then I can prove a special case of this question. Consider two smooth plane curves $C \equiv (X_C(s),Y_C(s))$ and $S \equiv (X_S(s),Y_S(s))$ represented in arc length parametrization. Curve...

r9m
r9m
user image
3
LOL
 
2 hours later…
06:36
Hey there, does anyone remember this post, I think it had a bounty, where the OP asked for a copy the some pages of a book, because his copy was unreadbale?
06:53
:/
 
2 hours later…
08:24
@r9m I feel safer about doing math now...
r9m
r9m
08:41
@robjohn sure :) No one looses ge******a for the sake of generality :)
09:13
Morning MSE people! Once upon a time I wasn't generic enough, alas! my genitalia is not guaranteed...
09:41
This just goes to show that assmptions are an important reproductive decision even in math.
10:08
First time in this chat, wonder what is happening here, given that there is this wonderful awesome M.SE. Are people just chatting about soccer and stuff? :)
Huy
Huy
Football.
And yes, Germany will win tomorrow.
I was asking this question recently: math.stackexchange.com/questions/837054/… Even gave bounty, but didnt get any answere. Do you know how to improve the question?
Huy
Huy
I'm sorry but I don't.
11:12
Hello!
I have one problem with wording.
In English language, what do you mean by "adding decimals"?
To the English speaker, what is a "decimal"?
If I understand this correctly, Americans say "adding decimals" when they mean adding the fractional parts of two decimal numbers. Correct?
Like with 7.056 + 5.67. Here "adding decimals" refers only to adding 56 thousandths and 67 hundredths? Right?
But the entire number 7.056 is a decimal number, and so is 5.67. No?
I know that deci means ten, and it's a decimal (or base-10) numeral system. So in your world, why are the 5 and the 7 not considered to be "decimals"? I don't understand this...
11:58
People loosely refer to "decimals" as what is strictly called the decimal representation of a number.
Hi people! I've just made a question concerning integration of a Gaussian-like function, over some region. @DanielFischer, you answered a very similar question 8 mothns ago, but I cannot find the way to connect them... You'll find the link above. If you'd like, take a look! Thanks~!
ALSO, please feel free to edit the title of the question!
ALSO, feel free to upvote if you believe it's an interesting question! For me it's not only interesting but also absolutely useful for me to go ahead!
12:13
@sammyg Do you have some context? Just seeing "adding decimals" doesn't mean anything to me.
 
1 hour later…
13:23
@skullpatrol Would a whole number like 7 be considered a decimal representation? I mean you could add a bunch of tailing zeros like 7.00000.
@robjohn Like with 7.056 + 5.67.
@sammyg yes
either way it is a decimal representation
@skullpatrol So in a number like 7.056 both the 7 and the 6 are "decimals"?
"A Decimal Number is a number that contains a Decimal Point" mathsisfun.com/decimals-menu.html
@sammyg Your question was about the phrase "adding decimals". In what context is that phrase used? You have just restated part of your previous question.
13:27
@sammyg that is true also
@sammyg That definition is odd. A decimal number is one expressed in base ten.
@sammyg this is a better reference.
@robjohn In other words even a number like 120 is a decimal, because it can be expressed as 12*10^1. Right?
@sammyg They are comparing fractions to decimals
this is where 3/2 and 1.5 are compared
@sammyg it is a decimal number if it is base 10. We assume base ten unless otherwise specified, so yes, 120 is a decimal number.
@skullpatrol So? For a number to be a "decimal number", it doesn't necessarily have to be of the form "7.056" with a decimal point, whole number parts and fractional parts. The number "8" might as well be considered a decimal number. No?
13:36
Yes. 8 is a decimal number
deci means ten, and it's a decimal (or base-10) numeral system
Apparently "decimal" comes from medieval Latin word "decimalis" which means "of tenths". In Latin, "decimus" means tenth, and "decem" means ten. So maybe that's why by "decimal" (at least in early and informal math) we mean the decimal representation of a number with fractional parts.
yep
a decimal point is a dot used before a decimal fraction
$7\frac{1}{2}=7.5$
So how's that? Do you buy that? :) That's a new one for me at least, so "decimal" really means tenths, not ten. I mean in this sense, "decimal" really means a number that has fractional parts. So the number 7.086 would be a "decimal" and a number like 8 would be just a regular (whole) number, or "decem" perhaps.
true, when you first learn counting, you start with the whole numbers, and then the fractions, and then the decimal system
1/2 = 5/10 = 0.5
is there a meta thread for undelete requests?
13:50
@sammyg If you want a discussion about the etymology of the word, try English Language & Usage :-)
healthier recently axed this question and I think the answers are funny, but one of them is mine so I don't want to unilaterally undelete it.
@AlexanderGruber As far as I know, there is just this thread for reopen votes.
@robjohn does anybody else use that for undelete requests or would I be the first?
@AlexanderGruber I don't know. You'd have to look through the posts there.
@sammyg "decimal" really means counted in tenths or tens
13:55
@skullpatrol So in this sense "decimal number" really means a decimal representation of a number with decimal fractions? The word "decimal" is used as a synonym for "decimal fraction"?
@skullpatrol ok
@skullpatrol I'm afraid they will send me back here, or back to the school bench. :P
@sammyg Have you tried looking up the definition in a good college dictionary?
@AlexanderGruber Why your answer here math.stackexchange.com/questions/865092/… was not correct?
@Nico i read the question as, "assuming that $G,G^\prime$ are conjugate in $\operatorname{GL}_n(K)$, are they conjugate in $\operatorname{GL}_n(L)$?" but then I reread the question and it instead asks, "assuming that $G,G^\prime$ are conjugate in $\operatorname{GL}_n(L)$, are they conjugate in $\operatorname{GL}_n(K)$?"
@skullpatrol Best I could find was urbandictionary.com. ;-)
@AlexanderGruber Ah okay, thanks.
14:02
@sammyg :D
urban math
@skullpatrol Collage dictionary? Hmm... not sure what kind of dictonary that is. But I'm gonna guess it's one of those Oxford dictionaries. They are usually considered to be most authoritative ones on English language.
decimal: reckoned in tens or tens
"Relating to or denoting a system of numbers and arithmetic based on the number ten, tenth parts, and powers of ten" oxforddictionaries.com/definition/english/decimal?q=decimal
adjective^
decimal (noun): decimal fraction
fraction with 10 as denominator
expressed in figures after a dot
Thanks @skullpatrol that was really helpful.
14:14
Thanks for asking :-)
Now speaking of urban math... it looks like these guys could need some help with decimal fractions. What are the common sizes coke is sold in?
14:47
@r9m hey.
@r9m
@r9m here?
@r9m
@r9m Wake up! :'(
@BalarkaSen hey
@Sawarnik did you try series expansion and diophantine approximations?
15:42
@robjohn did you? That's nice.
Greetings
$$
\begin{align}
\frac1{k^2n^2(k+n)^2}
&=\left(\frac1k+\frac1n\right)^2\frac1{(k+n)^4}\\
&=\frac1{k^2(k+n)^4}+\frac2{kn(k+n)^4}+\frac1{n^2(k+n)^4}\\
&=\frac1{k^2(k+n)^4}+\left(\frac1k+\frac1n\right)\frac2{(k+n)^5}+\frac1{n^2(k+n)^4}\\
&=\frac1{k^2(k+n)^4}+\frac2{k(k+n)^5}+\frac2{n(k+n)^5}+\frac1{n^2(k+n)^4}\tag{1}
\end{align}
$$
Therefore, exploiting the symmetry between $k$ and $n$, we get
$$
\begin{align}
\sum_{n=1}^\infty\sum_{k=1}^\infty\frac1{k^2n^2(k+n)^2}
&=\sum_{k=1}^\infty\frac2{k^2(k+n)^4}+\frac4{k(k+n)^5}\tag{2}
4
That's beautiful, @robjohn!
Great idea.
I used $$\sum_{n=1}^\infty\sum_{k=1}^\infty\frac1{k^an^b}-\frac1{k^a(k+n)^b}-\frac1{k^b‌​(k+n)^a}=\zeta(a+b)$$ for $a,b\gt0$ and $a+b\gt2$
If $a,b\ge2$ then the first term in the sum comes to be $\zeta(a)\zeta(b)$
@robjohn Nice. Here is the way I started ... (now I'm working on the last part)
as well as the result on $$\sum_{n=1}^\infty\frac{H_n}{n^q}$$
15:54
The last series is a known Euler series. @robjohn see above my first part of the proof.
@Chris'ssis yes, I cite my proof of it above.
@Chris'ssis The start is very similar. It is nice that nothing more than series manipulation is needed.
@robjohn Indeed.
Hey guys, hey Balark
16:09
hey @bolbteppa
long time no see!
Hi @Rob
1
Q: Question on Moment of inertia about center of mass of a smooth plane curve.

Rajesh DThis question is in continuation to this and motivated to answer this question. If I have an answer to it, then I can prove a special case of this question. Consider two smooth plane curves $C \equiv (X_C(s),Y_C(s))$ and $S \equiv (X_S(s),Y_S(s))$ represented in arc length parametrization. Curve...

I have edited the following, just in case someone is interested in: math.stackexchange.com/questions/865051/… cc @DanielFischer
16:32
@robjohn the last series in my proof I showed you is pretty tough if you want to do it elementarily.
@RajeshD I see... how are things otherwise?
@Chris'ssis The image that has been deleted?
@robjohn Yeah.
@robjohn $$\sum_{n=1}^{\infty} \frac{1}{n^4} \left(1+\frac{1}{2^2}+\cdots+\frac{1}{n^2} \right)$$
@Chris'ssis Ah, that one gets paired with the series with the $2$ and $4$ exponents switched and the sum of the two is simple
@Chris'ssis That is $$\sum_{k=1}^\infty\frac{H_n^{(2)}}{n^4}$$
@Chris'ssis Do you have a closed form for it? or for $$\sum_{k=1}^\infty\frac{H_n^{(4)}}{n^2}$$
@robjohn yeah
@Chris'ssis The sum of those two is very simple, luckily: $\zeta(2)\zeta(4)+\zeta(6)$
16:41
@robjohn I know (one way is the summation by parts).
@Chris'ssis to get the sum of the two, or to get just one sum?
@robjohn to get the sum of two.
@Chris'ssis Oh, it's even simpler. You just notice that they sum to $\zeta(2)\zeta(4)$ but repeat the diagonal.
$$\sum_{n=1}^\infty\frac{H_n^{(2)}}{n^4}=\zeta^2(3)-\frac{\zeta(6)}{3}$$
@Chris'ssis Oh, wait. I think I can get that from my answer, too.
@Chris'ssis Is there a nice formula for that with a general positive integer exponent in the denominator, as there is with the standard Harmonic numbers in the numerator?
16:51
@robjohn there is something, but it's not our case here. See $26$ and $27$ here - mathworld.wolfram.com/EulerSum.html
@Chris'ssis It's interesting that $m+n$ needs to be odd for those formulas.
@robjohn Yeah, I know.
17:25
@robjohn My proof wasn't optimized enough. I need to change some things there.
Howdy @Chris'ssis, @robjohn, et al.
@robjohn I'm going to finish it in a very brilliant way. I burn out some of my way and restart it from a certain point.
@robjohn: I have a query for you.
@TedShifrin Hey! How is it going there? :-)
17:32
So we have the famous secretary problem, for which the optimal strategy involves the number $n/e$. And then if we want to maximize the product of positive numbers whose sum is $n$, we again choose $n/e$ equal numbers [ignoring rounding issues]. Are these two problems somehow related?
Doing well, thanks, @Chris'ssis ... getting ready to disappear for several weeks :)
@TedShifrin Ohhhh Nooooo :-)
Not like Jasper or Balarka. I'm going on vacation :P
:D Then, have fun!!!
Thanks, @Chris'ssis.
18:03
@TedShifrin Have a nice vac(cin)ation. When will you leave?
What could I use to prove that for any real number there is a sequence of rational numbers that converges to it?
@user60887 What have you to work with? Which definition/construction of $\mathbb{R}$?
I came up with it. I'm pretty sure I have to use the density of the rational numbers
18:20
@user60887 The denseness of $\mathbb{Q}$ in $\mathbb{R}$ is pretty much equivalent to the existence of sequences of rational numbers converging to any given real number. How you prove it depends on which definitions you use (and which theorems are already proved).
Oh i see. So pretty much there really is not much to the proof?
That depends on what you have. It can be trivial, or not.
Well my book states that by definitions A set $S$ of real numbers is said to be dense in $\mathbb{R}$ provided that every interval $I=(a,b)$ where $a<b$ contains a member of $S$. The theorem states the set of rational and set of irrationals are both dense in $\mathbb{R}$ which is proved.
Okay, so what remains is to show that from that you obtain convergent sequences.
Yes, which is what I want to prove now.
I was thinking let $r$ be a real number and $q_n$ be a sequence of rational numbers. Suppose force $|q_n-r|<\epsilon$.
Hi Prof @Ted @Balarka
@Studentmath ! :)
@TedShifrin It looks like both problems reduce to (finding the maximum of) $x^{1/x}$. I haven't really analysed the secretary problem, however, to see how it appears there.
It's actually $x\log x$ there. But I'm wondering if there's deeper connection.
$-x\log x = \log \left(\frac{1}{x}\right)^x$
18:46
I know, I know :) stop avoiding my question :D
@user60887 Consider the intervals $\left(r-\frac{1}{n},r+\frac{1}{n}\right)$.
r9m
r9m
@Sawarnik Hey ... wassup ? :D ... I was sleeping actually :| .. such a nice weather :P (perfect for sleeping :P ... )
19:17
jao
19:48
oh i see thanks
@N3buchadnezzar ahoy
holydays < 3
20:19
@TedShifrin I am back. What's up?
Heya @TedShifrin
Anyone interested in taking a look at:
3
Q: Interesting Summation Congruence

ruadanLet $5\mid a$, $\gcd(a,b)=1$, and $b\equiv 2\bmod 5$. How can one show that $\sum_{k=1}^{a}k\lfloor\frac{kb}{a}\rfloor\equiv 2\bmod 5$? Similarly, can we show that if instead $b\equiv 3\bmod 5$, then $\sum_{k=1}^{a}k\lfloor\frac{kb}{a}\rfloor\equiv 3\bmod 5$? EDIT: These appear to be special c...

21:18
Hi @Balarka
21:57
Hi MSE people, I wonder if I am the only one (maybe plus $3$ other users) who think this question deserves an answer: math.stackexchange.com/questions/865051/…
"deserves"?
Don't be pompous. It may well deserve an answer, but first someone who understands the question and has a good answer for it has to come upon it.
@TedShifrin, ok, in the sense that it would be nice if it had an answer..
I didn't mean to be pompous! Honestly!
Well, I'm sure that if the conditions I mentioned were met, that person would answer it.
@TedShifrin, I guess you're right, I am bit disappointed, though..
It's quite technical and there's a lot of notation. I have no doubt that there are people around who can understand it, but I — being far from an expert in this kind of stuff — can barely make sense of it.
22:03
@TedShifrin, thanks for taking a look, anyway!\
I saw "Athens" in your profile, I got surpsrised for a sec! I'm from Greece, that's why!
@nullgeppetto I have no idea how one could evaluate the integral in the general case. Of course if you have specific data, you can numerically evaluate it, but an analytic solution, if at all possible is beyond me.
LOL, sorry, no, in the US lots of states like to steal historical names ... Athens, Rome, Sparta, Cairo ... all in the state I'm in.
Hi @DanielF
Hi again @Ted
@TedShifrin, even the word "pompous" comes from the greek language! :)
3 - 0
Brazil is dreadful.
22:10
LOL ... @nullgeppetto, no I rather think it comes from Latin :)
@TedShifrin $\text{Gal}(\Bbb C/\Bbb Q)$
totally uncountable, @Balarka
@TedShifrin it's not.
oh, well, are we back to topological considerations? Algebra doesn't know those.
no, we're not. it's not uncountable. it's not even defined.
$\Bbb C/\Bbb Q$ is not galois
=P
22:12
@robjohn that last sum in my proof is tremendously difficult.
@TedShifrin, no, it somes from the greek word "pompi" which means procession/pageant!
It comes from Latin pompa, too, @nullgeppetto :D
@TedShifrin $\text{Aut}(\Bbb C/\Bbb Q)$ is uncountable, on the other hand.
Who cares, @Balarka. To me the notation means the automorphism group. Pfeh :D
@TedShifrin tsk tsk subtleties must not be forgotten.
22:14
@TedShifrin, yeah, maybe, I won't argue about that! Personally I belive that is originally comes from the greek word, but it doesn't matter at all!
It's a matter of convention/definition.
@TedShifrin Gal is universally defined to be galois group of algebraic extensions.
Well, fine then. sticks out tongue
I know a lot of languages, @nullgeppetto, but no Greek. I'm sure there are a lot of places where Latin and Greek overlap.
@DanielFischer, I was afraid of that. The truth is that I need an analytic solution, which I believe (intuitively) that is nor possible. I'am thing of solving the first problem (that problem you solved $8$ months ago), and then apply Hilbert Spaces theory...
@TedShifrin Peter L. Clark (you know him?) on the other hand conjectures some kind of FT for transcendental galois extensions.
22:17
I know him extremely well, @Balarka.
To what extremity, @TedShifrin?
Urk. I'm afraid your intuition is right there, @nullgeppetto. But I'm not an integration guru, so I could be wrong.
We're colleagues, @Balarka.
@TedShifrin, yes, that's true, for sure. However, the Greek civilization is much older than the Latin, despite the fact that nowdays Greek people (in general, not only politicians) are extremely unappropriate to handle this legacy...
LOL ... The world in its entirety is a mess, @nullgeppetto.
22:18
@TedShifrin ... He is in UGA too?
@TedShifrin Colleagues as in "at the same university"?
yes, @Balarka
in the same department, one floor apart, @DanielF ... we talk quite a bit.
@TedShifrin He is a number theorist.
That reminds me: If @Pedro actually visits, I need to make sure he meets Pete.
Yes, @Balarka, I do know that.
Although he is teaching point-set topology next spring :D
Seems to be a good man, @Ted, judging by his posts on main.
22:19
groans
Thanks once again @DanielFischer! I will put some thought to it, and I'll wait for a good integration guru!
Very smart man, @DanielF. We have definite disagreements on pedagogy/teaching, but he'll have the last word, as I'm quitting :P
Hmm. Probably $Aut(\Bbb C/\Bbb {\bar Q})$ is much more interesting.
@blue and I were discussing things verging on this a few weeks ago, @Balarka. Only issues of pure transcendence versus not.
22:21
@Balarka, let Pete inspire you to be more well-rounded :P
@TedShifrin, I couldn't agree more with you... It's a very bad luck we have been born as humans... Human is the worst "thing" the planet ever saw. Fortunately, there are Mathematics!
LOL, indeed, @nullgeppetto, and I'm sorry for the harshness of "pompous" :)
@TedShifrin I'm only a beginner. Have mercy.
Attitude, @Balarka. When I was your age and quite older, I wanted to learn everything.
@TedShifrin And that'd lead to jumbling up stuffs.
22:23
@TedShifrin, no worries! To tell the truth, it was a bit of a pompous!
Jumbling is, in the end, good, @Balarka. It means you're thinking and being challenged.
Reading several stuffs at once is never a good idea, IMO.
Actually, Pete knows a ton of mathematics ... and takes pride in it.
That'd lead to superficial understanding of each of them.
I know less of a ton, but different stuff from him :P
22:24
@TedShifrin I know NTst who knows a ton of mathematics. And I am not inspired.
No, @Balarka. That is wrong. But you have a young brain. It's not used to multitasking.
Terry Tao is a Ntst yet a real analyst. Weird guy.
Well, that's too bad, @Balarka. I was extremely inspired by some of my teachers in college and, particularly, in graduate school.
No, he's an analyst first and foremost.
@TedShifrin shrugs
My adviser was one of the most famous mathematicians of the 20th century, so I felt very honored that he worked with me.
22:26
I think I'll rather do one thing at a time.
I'll continue this discussion with you when you're 22.
Well, several things are good, but several unrelated things are probably not so good.
... if I'm still alive :D
@TedShifrin if you're still alive.
JINX
@TedShifrin Are you familiar with motives?
@BalarkaSen, you're really 14?
22:28
@nullgeppetto me? what me?
oh, no, i am 41
early return button!
a computer scientist living in Australia.
i have written some papers with don knuth, as a matter of fact.
@BalarkaSen, ok you're kidding me?
22:30
Hush up, @Balarka.
I already gave @nullgeppetto a hard time :P
BTW, @nullgeppetto, why did you pick an Italian name if you're Greek? :)
@TedShifrin, it's a long story.. Because of my surname.. It's Tzelepis (ok, it might not make sense). That happed many years ago, I was an innocent child back then. I liked it, though, and I kept it. As for the null, when I grew up, start reading poetry and living, I was impressed by the "Zero"..
It was the geppetto I was thinking of. :) Or are you really Pinocchio with a growing nose?
There was a greek poet, K.Karyiotakis, who's work was about zero, infinity, and death.
22:36
Well, those issues are reasonably universal :)
@TedShifrin, true! But, no, I am not a liar!
LOL :)
Can $\mathbb{Z} \oplus \omega \mathbb {Z}$ be embedded in a field?
\oplus, @Balarka
What about $\mathbb C$?
$\omega \in \Bbb C$
@TedShifrin Nah, too general.
I want a minimal field, I think.
22:39
Excuse me. You asked for a field.
Is $\omega$ algebraic over $\Bbb Q$?
Yes.
Who starred that?
Then it's $\mathbb Q(\omega)$.
@TedShifrin Right.
I was being a fool.
I would not be so harsh, but I have to prove I know something. :D
OK, question : is $Aut(\Bbb C/\Bbb Q(\omega))$ trivial?
I guess it is.
22:41
Of course not.
Go to sleep, @Balarka.
you're right. it's 4:11 am here.
Night.
Have a good night people! It's ~02.00 am here and I believe it's high time I made a coffee, leave the chatroom, and start integrating!\
Take care, @nullgeppetto :)
i was trying to give an analogy to $Aut(\Bbb R/\Bbb Q)$
22:42
Not even close, @Balarka.
@TedShifrin, :) you too, thanks!
Well, that, too, is uncountable unless you impose continuity, @Balarka.
yeah, i am imposing continuity.
otherwise it's a boring group.
No difference between $\text{Aut}(\Bbb C/\Bbb Q)$ and $\text{Aut}(\Bbb C/\Bbb Q(\omega))$
QO?
QO/O?
22:44
Hush.
OK, if you won't go to bed, I'll leave and cook dinner :)
Have mercy.
22:59
@robjohn I can easily compute that last series if I use your work (or better say, that relation) above. By the way, that relation you used to solve my question it is somehow familiar to me, I saw it ... (in a proof by Spivey?)
23:12
heya @Kaj

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