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8:00 PM
@Huy I respect Ted because he is older than me, so that's why I have no intention to argue with him. Just try to behave polite in front of him
 
Huy
@Alizter: No, but I was told repeatedly that this kind of language shouldn't be used in this chatroom "because there's kids", so I flagged it and other people agreed with me, apparently.
 
If a 14 year old said something vulgar to me or around me I would just dismiss it.
 
This argument is a new definition for the phrase "beating a dead horse"
 
Huy
@BalarkaSen: The use of the p word with the verb is a vulgar expression for a certain activity. You'll probably learn about it when you're a bit older, if you really don't know yet.
 
I think there is a difference between every other sentence containing vulgarity and one vulgarity occasionally.
 
8:02 PM
I have just known that "kissing" is considered to be vulgar word in English term.
 
@Venus really?
 
Huy
@Alizter: Of course there is.
 
@Alizter According to Ted, I assume so
 
@Venus That is Ted's opinion. Not fact. But I respect Ted therefore I respect his opinion. Does not mean I agree.
 
@Huy wait, so you're saying that pus doesn't really mean what it usually means?
 
8:03 PM
@BalarkaSen Did you really say pus?
 
Huy
@BalarkaSen: In that context, it means something different.
 
@Alizter yeah, i did.
 
Huy
@BalarkaSen: You said said something else at first, then edited to "pus".
 
At the end of the day
 
He edited it from something else, but the word was "pus"
 
8:04 PM
i said puss at first, @Huy
that was a typo
 
@Alizter What I have said is sarcasm
 
and is not vulgar either
 
Huy
@BalarkaSen: I can't check on that.
 
Then you can't possibly flag @Huy
 
I do respect Ted too
 
Huy
8:05 PM
@BalarkaSen: It is vulgar either way.
 
At the end of the day, people who interpreted PE as "Physical Education" and "Pus Eaters" are merely observers of @Huy's comment. The real meaning is with the observer.
And no craps were given from that point forward.
 
@Alizter LOL
 
Good to know that people flags in here for no reason. I'd try to flag every possible vulgar word in every sentence from now on then.
 
Pus, noun
1.
a yellow-white, more or less viscid substance produced by suppuration and found in abscesses, sores, etc., consisting of a liquid plasma in which white blood cells are suspended.
 
8:08 PM
And that's not at all vulgar.
 
Huy
@teadawg1337: There are a lot of words which by themselves are not vulgar, and you're old enough to know that they can be when used combined with other words.
 
Guys, cut it out
 
@Huy Hey, don't drag me into this...
 
We are only beating a dead dog
 
No way. If I say "a" then people can also infer vulgar stuff out of them.
Does that mean it's good enough to flag?
 
8:09 PM
Hey!? I said cut it out.
 
Let's talk about math
 
Balarak
 
how about that $$e^{i \pi} + 1 = 0$$?
 
I need to come up with an idea of rational cardinaility
 
Huy
8:11 PM
@Mitch: It's actually -2.
 
First extending the idea of a set might be a good idea
But yeah. Combinatorics maybe the way to go
 
Already been thought before @Alizter
 
Hey, @Mitch. ^_^
 
Fuzzy sets
 
@BalarkaSen Of course it has
 
8:11 PM
@Huy hm that would at least get another important constant in there.
 
just now
 
I'm thinking about this integral $$\int_0^\infty \frac{x}{\sqrt{e^x-1}}dx$$
 
@Khallil Hey!
 
to talk
 
@Venus why doesn't latex work in chat? disappoint
 
8:12 PM
How are you doing today, @Mitch?
(I don't think we've spoken before!)
 
@Khallil I am doing great.
 
@Huy It was ridiculous though.
 
@Mitch It does work
 
@Khallil I'm hardly ever in chat here
@Venus what did I do wrong?
needs two $ signs?
 
8:14 PM
@Mitch See @Huy chat
 
oh...also just noticed the first starred message
 
Do you have any ideas for the integral, @Venus?
 
@Khallil I do have
Can you evaluate it @Khallil?
 
@BalarkaSen How can the grade of a member be 0?
 
@Khallil It turns out so trivial ^^
 
8:19 PM
I don't know where to begin, @Venus!
 
Huy
I hate that some sites on SE are so USA-centered. :(
 
Really, @Venus? O_O
 
@Huy Perhaps because they are hosted in NY?
 
@Khallil Yep
 
Integration by parts?
 
8:19 PM
@Khallil No. A clever sub
 
Huy
@Alizter: Where a site is hosted doesn't necessarily have anything to do with what it's about.
 
Ok. I'll give it a go!
 
@Huy Yes it does. They have to obey US law.
 
Huy
@Alizter: And which part of US law states that the content of the site has to be US-centered?
 
@Alizter grade?
 
8:21 PM
@Huy I never said that was with my last statement. I merely gave you a counter example for the statement it replied to.
 
Huy
@Alizter: Okay, good for you.
 
@BalarkaSen The fuzzyness.
 
@Huy but yeah. It is run in the US. The staff are from the US. so the core members are probably from the US thus USing everything else. Is there a problem with that?
@BalarkaSen Fuzzy sets
 
@Huy What did you mean by the term US-centered?
 
8:22 PM
You mean degree?
Degree can't be zero. otherwise the set won't include it.
 
Hey guys, to ask a question about how to create a math poster, what tags would I use? I want to recreate blog.felixbreuer.net/2010/10/24/poster.html but I don't understand how
 
Fuzzy sets are sets where each element is associated to a certain real in (0, 1] @Alizter
 
Huy
@Venus: I meant that most questions are only relevant in the US, or the question is relevant everywhere but the answer only relevant in the US.
 
@Alizter He means that the culture of the content is US centered.
@Huy Even math?
 
Huy
@Mitch: A bit less, but also quite a bit.
 
8:24 PM
@Chris'ssis
0
Q: evaluation of the integral of a certain logarithm

AmadeusI come across the following integral in my work $$\int_a^\infty \log\left(\frac{x^2-1}{x^2+1}\right)\textrm{d}x,$$ with $a>1$. Does this integral converge ? what is its value depending on $a$ ?

 
@Huy Don't forget that the US is pretty much the reason we are speaking English right now.
 
Bullcrap, mathematics is culture-independent (except for recreational maths)
 
@Venus that one is boring
 
@BalarkaSen Weird. Wiki says [0, 1]
 
@Venus It's a mess. Wolfram Alpha says... you don't want to know.
 
Huy
8:25 PM
@Mitch: Often you'll find people talking about Calc 1,2,3,4 or something like that and I think many people in different countries have no idea what is supposed to be covered in those courses.
@Alizter: I think England would be the reason for that.
 
@Chris'ssis It means it's trivial! :D
2
 
@Alizter Maybe. Doesn't matter.
 
@Huy chat or in questions/answers?
 
Huy
@Mitch: Both.
 
@Venus :D I'm working on a nice result right now :-)
 
8:26 PM
@Mitch Really? I haven't checked it yet
 
associating an elt to 0 is as good as not including it
 
@Chris'ssis Well, that's good
 
Anyone know?
 
At least speaking in the sense of cardinalities.
 
I've reduced the integral down to this, @Venus. $$\int_{0}^{\infty} \dfrac{x}{\sqrt{e^{x}-1}} \text{ d}x \overset{u=\sqrt{e^{x}-1}}= 2 \int_{0}^{\infty} \dfrac{\log(u^2+1)}{u^2+1} \text{ d}u \overset{u = \tan\theta}= 4\int_{0}^{\pi/2} \log(\sec\theta) \text{ d}\theta $$
 
8:27 PM
@Huy The answer is that it's in mostly in English and US is the primary speaker of English so attracts more Americans. I bet Weibo is annoyingly Han-centric.
 
@BalarkaSen If it is 0 then it is not in the set. But it is?
 
@Khallil = @BalarkaSen ?
 
@Khallil That's correct!
 
@Chris'ssis Lol
 
@Chris'ssis Me? No.
 
8:28 PM
@Venus it was pretty disgusting. There's always a chance it didn't find the right simplification, but still, yuck.
 
That's for you @BalarkaSen V
 
@Khallil The fastest sub is $\tan t=\sqrt{e^x-1}$
 
@BalarkaSen So does that not make the meaning of an element not being in a set redundant.
 
Yep, that's what I did but in two steps, @Venus!
 
Who starred that -__-
They won't even get the context
 
8:29 PM
Is it bad that I don't know how to finish it off, @Venus? Haha!
 
@Khallil Yeah, I can see that
@Khallil You're kidding, aren't you?
 
Not even joking. ^_^"
 
@Hippalectryon I don't get the context.
 
@Hippalectryon What is wrong with star? I love star though
 
4 mins ago, by Balarka Sen
At least speaking in the sense of cardinalities.
 
8:31 PM
Oh OK. LOL.
 
OK, gotta go guys
 
@Venus Sya
 
See ya later, @Venus!
 
Bye everyone... ^^
 
Huy
Good night, @Venus!
 
8:32 PM
Hmm, I'm gonna give that integral a go
 
"Well, a Riemann surface is a certain kind of Hausdorff space. You know what a
Hausdorff space is, don’t you? Its also compact, ok. I guess it is also a manifold.
Surely you know what a manifold is. Now let me tell you one non-trivial theorem,
the Riemann–Roch Theorem"

— Gian-Carlo Rota’s recollection of Lefschetz lecturing in the 1940’s
I LOL at this.
 
Wow measures are awesome
 
@Balarka That is beautiful xD
 
Venus' integral, @teadawg1337?
 
@Khallil Yup
 
8:35 PM
In that case, do NOT scroll up!
I kinda ruined most of it in one post. ^_^
 
I've already gotten there, lol
 
Ah!
 
ok, i gotta go sleep.
 
Night, man!
Got any ideas, @teadawg1337?
 
@Khallil Sorry, I got distracted by YouTube. I'll try to simplify it now
@Khallil I think I'm onto something here, gimme a sec
 
8:46 PM
Any hints, @teadawg1337?
 
@Khallil I turned to polylogarithms, I'm not sure if this is the right way to go about this though
 
I think I've evaluated a similar integral which is kinda unnerving. I've never heard of polylogarithms before, @teadawg1337. That sounds complex (hard, not imaginary)!
 
Can anyone help me with measure theory?
If $E_1 \subseteq E_2$
Then $\mu(E_1) \le \mu(E_2)$ right?
 
@Alizter I believe so, but don't trust me as I've just started learning measure theory a few hours ago
 
However $\mu(E_2)=\mu(E_1\cup E_2) = \mu(E_1)+\mu (E_2) \implies \mu(E_1) = 0$
 
8:53 PM
@Khallil I've managed to get to $\displaystyle \frac{\pi^3}{6}-2\int_0^{\frac{\pi}2}\operatorname{Li}_2(\sin^2\theta)\,\mathbb{‌​d}\theta$
 
@Khallil Are you trying to solve that integral? I will give you some hints. Get rid of sec
rewrite as sin
and see if you can exploit symmetries of sin
 
I have a simple question for you all: What is the most brilliant way of computing $$\int_0^1 \operatorname{li}(x) \ dx$$?
 
Oh wait
 
Divide by $0$ and take logarithms on both sides, @Chris'ssis.
^_^
What's up, @Alizter?
 
@Khallil I was being an idiot about measure theory that is all
 
8:58 PM
Ah, gotcha!
 
Wait, I've completely screwed this up...
 
Now I also propose a new pack
$$i) \int_0^1 \left(\frac{\operatorname{li}(x)}{x}\right)^2 \ dx$$ $$ii) \int_0^1 \left(\frac{\operatorname{li}(x)}{x}\right)^3 \ dx$$
 
@Alizter What you wrote is wrong. Measures have disjoint additivity: if $E_1, E_2$ are disjoint, then $\mu(E_1\cup E_2) =\mu(E_1)+\mu(E_2)$.
 
Yeah
I saw that
 
My last legitimate step was $\displaystyle 2\int_0^{\frac{\pi}2}\operatorname{Li}_1(\sin^2\theta)\,\mathbb{d}\theta$
 
9:02 PM
I don't see how a probability is a measure space though
I am not sure if all events form a $\sigma$-algebra
or am I thinking about this wrong?
 
I've given up on it, @teadawg1337.
 
@Hippalectryon How do we integrate it by parts (cleverly)? $$\int_0^1 \operatorname{li}(x) \ dx$$
 
@Khallil $\sec x = (\cos x)^{-1}$
 
Ya. I know.
 
@Alizter Do you see how to actually show that if $E_1\subset E_2$, then $\mu(E_1)\leq \mu(E_2)$?
 
9:04 PM
So that negative can be moved out
 
Then mapping $\theta$ to $\frac{\pi}{2} - \theta$ yields a $\sin$ in the argument of the logarithm without changing the upper and lower bounds of the integral.
 
@MikeMiller no. If a probability space is a measure space or not
 
When you spoke of exploiting the symmetry of $\sin$, I got lost.
 
I mean, look at the definition of a probability space
 
oh
it has to be a sigma anyway
I was gonna say
Oh @MikeMiller btw. Fuzzy sets is kind of similar to my notion of a rational cardinality
 
9:07 PM
Hah? Isn't probability space a measure space with measure 1?
 
Fuzzy sets could also have a measure
hmmm
 
@Alizter My approach is still correct, right??
Of course it is, nvm lol
 
@teadawg1337 No idea about log integrals sorry :P
 
@Chris'ssis doing integrals is all about using clever tricks.
 
Can you do the one below, @Mitch?
$$\int_{0}^{\frac{\pi}{2}} \log(\sec \theta) \text{ d}\theta$$
 
9:16 PM
$\displaystyle \frac{\mathbb{d}}{\mathbb{d}\theta}(-\log(\cos\theta))=\tan\theta$
Maybe that's useful somehow???
 
@Mitch Yeah, one needs to learn, create tons of clever tricks :-)
 
@Integrator iron man = fe male, since iron = fe
 
Huy
@Khallil: Can you do this one? $$\lim_{x \to 0} \frac{\sin(\tan x)-\tan (\sin x)}{\arcsin(\arctan x) - \arctan(\arcsin x)}$$
 
@robjohn please how to prove that $(u_n)=n$ on $(0,+\infty)$ is not a sequence of Cauchy ?
 
I give up, I shouldn't be doing any mentally rigorous activities when I'm sick anyway
 
9:20 PM
@Vrouvrou, isn't Cauchy equivalent to convergent? Since $\displaystyle (u_n)$ isn't convergent, it equivalently can't be Cauchy.
 
@Chris'ssis right, it's one area where the more you practice, the more tricks you pick up , so at the end to the outsider it looks like magic, but by the practitioner it's just 'oh I did this and this and it obviously works! Oh and I forgot this and this."
@Khallil ha ha, no, not at all. I was just glad to see that you had already reduced to that from the original.
 
Ah, cool!
I'd think about some algebraic manipulation before trying L'Hopital as it evaluates to $0/0$ off the bat, @Huy.
 
@Mitch Yeah, it requires a completely crazy amount of work, I mean some people would be terribly discourage if I told them from the beginning the long way to go ... After a while you look at a very crazy looking integral and know what to do ... (in just a few seconds)
 
There's no guarantee the answer is simple, even if the inside starts out simple (e.g. log integrals)
 
Huy
@Khallil: You can try. BTW, nice goal from Gerrard.
 
9:22 PM
@Vrouvrou we have $|u_n-u_{n+1}|=1$ for all $n$. For a Cauchy sequence, for any $\epsilon\gt0$, you need to be able to find an $N$ so that $n,m\ge N$ means $|u_n-u_m|\le\epsilon$. The statement I made says that this is impossible for $\epsilon=\frac12$
 
@Khallil we have allwayse the equivalence ?
 
@Chris'ssis but it's fun puzzle solving (especially since there's no decision procedure...
wait, yeah there is.
 
@Khallil $\displaystyle 4\int_0^{\frac{\pi}2}\log(\sec\theta)\mathbb{d}\theta =2\int_0^{\frac{\pi}2}\operatorname{Li}_1(\sin^2\theta)\,\mathbb{d}\theta$
 
Dunno them @Alizter
 
......
 
9:23 PM
That means that $|u_n - u_{n+1}| \not< \epsilon$ for all $\epsilon$, right @robjohn?
Since we can choose $\epsilon$ as $1/2$ say and the Cauchy property won't hold.
 
@robjohn what we can conclude please ?
 
@Vrouvrou what can you conclude about what?
 
i have not seen the edet sorry
 
@Huy I believe I answered that on main...
 
Huy
@robjohn: I don't know, it was on one of my old problem sheets of calc 1.
 
9:29 PM
@Chris'ssis (@yourlastmessage) Good question, since this integral is directly related to Li
 
@Hippalectryon Do you want me to show you something terribly simple?
 
@Chris'ssis Sure. No heart attack please
 
@Hippalectryon $$\int_0^1 (x-1)' \operatorname{li}(x) \ dx$$ that's all
 
Yep, @Vrouvrou. A sequence is Cauchy if and only if it is convergent.
 
9:31 PM
@Chris'ssis That's so simple I now have eye cancer (jk, please don't hurt me)
 
Huy
@Khallil: Only in complete metric spaces.
 
@Hippalectryon The rest is a boring story.
 
I've not looked at metric spaces. I can only assume that we're working in a complete one at the moment, @Huy!
 
Boring stories are boring
People who are killed die
@Chris'ssis No
 
@Chris Oddly enough, I evaluated that just the other day...
 
9:34 PM
@Chris'ssis I don't have your memory
 
@Hippalectryon I think you like it :-)
 
@Huy here. Look down to the simpler approach.
 
I think I do too :)
 
Huy
@robjohn: I solved it with Taylor.
 
@teadawg1337 Really?
 
9:37 PM
@Chris Yeah, I have no clue how tbh
 
ahh lebesgue integration makes sense now
 
I just had a flash of brilliance and bam
That's been happening to me a lot these days lol
I've gotta go, I can't do any more mathematics with this killer headache
 
@Chris'ssis Do you have the generalized version ?
 
@Hippalectryon Not yet.
@Hippalectryon I suspect that there should be a linear combination of zeta function values.
 
Hi, how can we prove that $\exists \forall \implies \forall \exists $?
 
9:50 PM
@MarcGato That's too vague
 
@MarcGato Sorry, the other direction is not true.
 
@robjohn The book I am reading said that the convers in general is not true
 
@MarcGato yes, I read it backwards and corrected my statement, but too late
 
@robjohn ok no problem, do you now how can I prove this?
(I took some example it's seems correct but no idea how can we prove this 'kind' of statement)
 
@MarcGato There are many different systems of logic, a proof would depend on the particular system you are using.
This is why I generally stay away from proofs like this :-)
 
9:54 PM
@robjohn hum okay :-), in other hands I don't have any background on systems of logic this this why I was a bit lost.
 
@MarcGato think of it this way, the first statement says that there is an $x_0$ that makes a statement true in all cases. That implies that in all cases there is an $x$ that makes the statement true, in particular, $x_0$.
 
@robjohn yep, i will think of this way now. Much natural that what I wrote initially.
 
@MarcGato The converse is not true since there may be a different $x$ that satisfies the statement in different cases, but not one single $x_0$ for all cases
 
@robjohn thanks now i can continue the proof i am reading. It's a bit frustrating to jump some step in a proof..
 
You should try fuzzy logic
logical values can be 0 or 1 or between
in the interval [0, 1]
 
10:04 PM
@Alizter Can explain what do you mean? I don't understand your second sentence.
@Hippalectryon (Désolé je n'avais pas vu ton com)
 
@MarcGato There is a logic system called fuzzy logic. Rather than being true or false ie. 0 or 1 the values are in the range $[0, 1]$
 
@MarcGato Pas grave :)
 
@Alizter interesting I will read this this week end.. now I have lot of work ^^
@Hippalectryon problème des quantificateurs dans les preuves c'est un peu frustrant..
 
@MarcGato On s'y fait :)
 
@Hippalectryon Oui sauf que là cette propriété est utilisé alors qu'apparemment la preuve nécessite des connaissances en logique que je n'ai pas donc on doit juste s'en convaincre car c'est logique ;P
 
10:10 PM
@MarcGato Quelle propriété ? (je n'ai pas vraiment suivi)
 
@Hippalectryon celle ci : $\exists \forall$ impliqe $\forall \exists $?
implique*
 
@MarcGato C'est trop vague. Par exemple, c'est $\exists\alpha\forall\epsilon\Rightarrow\forall\alpha\exists\epsilon$ ou $\exists\alpha\forall\epsilon\Rightarrow\forall\epsilon\exists\alpha$ ?
 
la deuxième @Hippalectryon. Robjohn a répondu plus clairement :the first statement says that there is an x0 that makes a statement true in all cases. That implies that in all cases there is an x that makes the statement true, in particular, x0.
 
@MarcGato Ah ok :) c'est bon maintenant ?
 
@Hippalectryon Bha oui enfin j'avais compris. C'était assez claire mais apparemment la preuve est assez "chiante"
 
10:18 PM
Ok :)
 
So... apparently there's a comment vote per day limit, and I just hit it. :o
 
@Hippalectryon tu fais de la topo?
 
@MarcGato Pas vraiment. Je suis en prépa.
 
@Hippalectryon ah un taupin
 
10:24 PM
MP,PC,PSI?
 
d'acc, j'espère que ça se passe bien
 
Bof :/ ça pourrait aller mieux xD
 
lol, trop de boulot non? ou trop de temps passé sur MSE ;p
 
Un peu des deux :-)
 
10:28 PM
Ca marche, bon moi je vais dormir! Bonne fin de soirée (studieuse..) @Hippalectryon.
 
@MarcGato Bonne soirée !
 
Woha, already 20 candidates.
 
This is the mathematics room and not the moderator room, right?
Can anyone help me with this problem? math.stackexchange.com/questions/838827/how-many-triangles. The answer provided was incorrect.
Anyone still online?
 
10:48 PM
That looks like a lot of counting.
 
I got 28, but I'm doubting that that's correct xD
though that's just for the smaller individual triangles
i do know that i'm supposed to use "pie"
@Studentmath ^^
 
36 secs ago, by Mathy Person
though that's just for the smaller individual triangles
huh?
 
i counted 28 individual triangles.
 
Supposed to use pi? Why?
 
no not pi, pie. the principle of inclusion and exclusion @Studentmath
 
10:50 PM
@MathyPerson what do you mean by individual?
 
Ah. Yeah, probably.
I have no elegant method springing to mind, none at all. Doubt there is something overly elegant
 
@anon
@anon the smallest possible triangle to make
 
@Mathy
okay. so have you tried using the logic in the answer in your own way?
 
@anon not sure what you mean. can you clarify?
 
you said the given answer is incorrect. have you tried fixing it?
 
10:55 PM
@anon actually, i didn't think of that :p. I'll go do that right now
 
I'm not sure where the given answer is getting +15+8 from
surely though one needs to fully compute all of the triangles which have all three vertices in the array
 
Hi @anon Could you maybe take a look at this exercise?
http://math.stackexchange.com/questions/1052007/intersection-multiplicity-of-the-curves
 
@anon Oh, I think I see the issue. The person who wrote the answer is instead subtracting the triangles with three vertices for overcounting, but really the problem is asking how many triangles can be made with AT LEAST TWO vertices in the triangular lattice, not just two.
 
@MathyPerson that is not the problem, read it better
@evinda sorry it would take me awhile to get back up to speed in alg geo
 
@anon where did they get "1+3+6+10+15+8=43"?
 
10:59 PM
@anon A ok.. Could I ask you a question about flexes of a curve?
 

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