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12:11 AM
@Sawarnik That's not how proofs work :P. I find one counterexample and your theorem does not hold, and is thus refuted.
 
12:26 AM
Normally many people are here at this time
 
well, it is halloween
 
Oh I forgot about halloween
Noone mentions that in Australia
 
Oh it's 5:30-8:30 in America and it's Halloween, that would definitely do it
 
12:54 AM
hi, can any matlab people give me a hand with this question: stackoverflow.com/questions/26606297/…
 
1:38 AM
I don't get it. I have only discovered a handful of math chat rooms on the internet. Yet there must be millions of mathematicians in the English speaking world. Wouldn't you expect to see more than just 55 people in this room? I mean out of the entire world, there are just 55 of us in here?
 
They are busy actually doing math
 
@AbstractionOfMe I also find this sad. But as time goes on, more users will come, and I would guess at exponential growth
 
32
Q: How many mathematicians are there?

Georges ElencwajgAlthough we are not so numerous as other respected professionals, like for example lawyers, I wonder if we could come up with a reasonable estimate of our population. Needless to say, the question more or less amounts to the definition of"mathematician". Since I should like to count only resea...

 
@user130018 That number is shockingly low.(I don't doubt its rough magnitude though)
 
So is my white blood cell count
 
1:46 AM
@user130018 @Committingtoachallenge interesting
 
2:02 AM
Lol @user130018 lawyers being respected :P
 
@user130018 Why is your wbc count low?
 
@AbstractionOfMe What is 'wbc count'
White blood cell?
Oh I see there
 
ya @Committingtoachallenge
eating chicken, havin greasy fingers, and typin with knuckles leads to such abbreviations
 
@AbstractionOfMe Fair statement
How did @justabrickinthewall change his name so quickly? I thought it was once every $30$ days?
@KajHansen Has anyone told you that you look like Leonardo DiCaprio?
 
2:20 AM
@Committingtoachallenge, several people have told me this on MSE chat alone.
:P
 
Not coming up in the search though, I thought I was unique </3
 
Oh, I think they either posted a picture or mentioned the name of his character in a movie.
I get Matt Damon every now and then in here too.
 
I think @KajHansen looks more like Matt Damon
 
Ugh...working through problems from chapter 3 in Baby Rudin. Analysis certainly doesn't come naturally to me.
 
@KajHansen post questions on that - I can actually help!
 
2:35 AM
I gave up on Rudin after page 9
 
math.stackexchange.com/questions/1000606/… I'm also going to bump this before my shower, cya in a bit also @user130018 which Rudin book?
 
PMA
 
....?
 
@AbstractionOfMe today I was talking to a lecturer about knots we cannot draw, he brought up a knot with more crossings than particles in the universe, obviously we cannot draw that but this isn't the same as "it's not expressible on paper"
 
2:44 AM
@user130018, Chapter 2 and probably subsequent chapters are far more easily understood than Chapter 1 IMO. The proofs he gives for chapter 1 are rather unmotivated and can be simplified a lot - e.g. his proof of the density of $\mathbb{Q}$ in $\mathbb{R}$ is unnecessarily opaque. I struggled through reading lots of his chapter 1 proofs, whereas I can leisurely read chapter 2 before bed.
 
@KajHansen That's exactly the proof I quit the book at
@KajHansen I asked about it on here (MSE), and the explanation used concepts I would never have thought of (that Rudin leaves out)
 
@user130018 that's because they're boring choirs!
 
@AlecTeal Choirs!
 
Stuff goes a lot faster if you're motivated, he wants to talk about not chapter 1, but he has to so everyone gets the same definition.
Typo, I'm sure you can work it out.
 
@AlecTeal what does that have to do with three types of mathematician?
 
2:48 AM
@user130018, there are definitely proofs of that fact that are much more intuitive.
 
hi, can any matlab people give me a hand with this question: stackoverflow.com/questions/26606297/…
 
But yea, I got rid of Rudin because I hate it so much, so I don't have it anymore
 
@AlecTeal, I'm not stuck enough to post on MSE, but I do feel like these are taking me longer than they should. :P
 
@KajHansen then move on :)
 
Naturally. But they are part of this week's problem set, so I'll have to do all of them eventually ;)
 
2:52 AM
 
@KajHansen Hello there.
 
@KajHansen I didn't read that book in order, first chapter seems to be absent!
 
Hey there @Pedro. Talking to each other through two mediums at once. :P
 
But seriously @KajHansen don't read in order, it's boring! Also seeing how the theorems you want to prove often helps you get a feel for them, which really helps!
@PedroTamaroff math.stackexchange.com/questions/1000606/… please, I cannot take my own advice and just move on (not a word @KajHansen)
 
@KajHansen Hehehe, yes.
@KajHansen So say you have a class of Cauchy sequences $[x_n]$.
I take you define $D([x_n],[y_n])=\lim d(x_n,y_n)$.
 
2:56 AM
Indeed
 
And you know already that $X$ is dense in $\hat X$.
 
Well, we are actually asked to show that fact. But I can see it intuitively.
 
Well, since $x_n$ is Cauchy, given $\varepsilon >0$ there is $N>0$ such that for any $n>N$, you have $d(x_n,x_N)<\varepsilon$.
Then $[x_n]$ is $\varepsilon$-away from the class of the constant sequence $x_N,\ldots$.
 
Ok, makes perfect sense.
 
Since $\lim_{n\to\infty}d(x_n,x_N)\leqslant \varepsilon$.
Well, now say you have a Cauchy sequence $X_n$.
 
3:00 AM
Sure, I'm with you
 
For each $X_n$ you have a constant class call it $Y_n$ that is $1/n$ away.
And $D(X_n,X_m)\leqslant D(X_n,Y_n)+D(Y_n,Y_m)+D(Y_m,X_m)$.
 
Ehhh, where is your $\frac{1}{n}$ coming from?
 
Well, I took $\varepsilon=1,1/2,\ldots$.
For $X_1$ I took $1$.
For $X_2$ I took $1/2$.
 
Oh cool, there we go.
 
3:02 AM
I could have actually helped with that!
 
Right, so $D(X_n,Y_n)\leqslant 1/n+1/m+D(Y_n,Y_m)$.
Where $Y_n,Y_m$ are classes of constant sequences.
 
Yeah, and a lot of this motivation comes out of the previous problem I just finished.
 
Say $y_n,y_m\in X$. So $D(Y_n,Y_m)=d(y_n,y_m)$.
@KajHansen Oh, really? Let me see the book.
 
Check out problem 3.23 in Rudin.
@AbstractionOfMe, that was my response. What's up?
 
@KajHansen OK, I found it
 
3:07 AM
Actually I was asking for an explanation of the comment "This answer is proof there are three kinds of mathematicians: those who can count, and those who can't."
 
Yes, it is basically asking you to do all this.
 
Ah, sorry about that @AbstractionOfMe.
 
@AbstractionOfMe It is a freaking joke.
 
@KajHansen Although it is true that I got to that question because I wanted to check your likeness to Matt Daemon
 
@PedroTamaroff, it definitely guides you right through step by step. I've been working on my problem set for a few hours now, and I haven't actually started working on #24. I simply read it so that my subconscious would chip away at it while I relax.
 
3:09 AM
@KajHansen So it suffices you show that $d(y_n,y_m)\to 0$.
 
@AbstractionOfMe, LOL
 
@KajHansen Sorry, I am telling you stoopid things.
You have a Cauchy sequence and you want to see it converges.
 
@PedroTamaroff, I noticed ;) We already have a Cauchy sequence, and we want to show convergence. I'm sure that won't be a problem given my work from #23 though.
 
#23 only helps you to show that the metric is well defined.
The point here is that if you have a sequence of Cauchy sequence, the convergence point will be the diagonal.
Well, or any other cofinal thing to that.
 
Thanks a bunch for your help @Pedro. Hopefully I can finish up this set tomorrow afternoon :P
 
3:22 AM
Good luck
 
Hi @Pedro @Kaj
 
Hey there @TedShifrin. It seems Fu assigned us a markedly more substantial problem set this week now that half his class is gone.
 
Good!
 
Hi too
 
Hi @Alec
 
3:31 AM
Thanks
I really hope the questions pick up soon, I'm primed to answer something!
 
Indeed @Ted. I've been cracking away at it for much of the day. Plus we finally got a challenge problem on this set.
 
About 1/3 my prob class got Ds and Fs, so I'm almost as angry as he was.
 
D:
1/3 !
 
That's how that course should be :)
 
How do I get more precision in my output for mathematica(output longer)?
I am getting 5 decimal points
 
3:35 AM
@Committingtoachallenge, I was having the same problem in Python! It's a pain in the ass, no doubt.
 
The only question I've answered was a first week diff geo problem, and when I told the OP to use basic first semester calculus, he wanted me to give him the solution. I refused. I suggested reading the problem would be good. I'm such a bitch.
 
@TedShifrin, what are you referring to? On MSE or in office hours?
 
@Committingtoachallenge: use N[...,10] or whatever ...
on MSE
It was your first required problem last spring, @Kaj.
 
AH yes, I'm looking at your response :P
 
I'm sure Rene or someone will swoop in and do it. Actually, that problem has been done on here at least 2 or 3 times.
 
3:40 AM
I can probably do this question, what is it?
 
@TedShifrin Thank you Ted, that did it!
 
Don't do the guy's homework
sure, @Committingtoachallenge
 
@TedShifrin I try to ask "what did you do" first, or I don't complete it, or solve a different question with the same method.
 
So apparently one can find a parabola with vertex at the origin such that it's arclength inside the unit circle centered at $(0, 1)$ is greater than $4$. Incredible.
 
Proof or it didn't happen
 
3:43 AM
@AlecTeal, I'm thinking about cracking away at it. It's apparently a Putnam problem that one of my friends just sent me over FB chat.
 
Hmm @Kaj: I believe close to 4 ....
 
You can get close to 4 by going steeply down to zero then back up! The steeper it is the nearer to 4.
 
but curvature adds length !
 
@TedShifrin, it is problem A6 here: cs.berkeley.edu/~wkahan/MathH90/SPutn01.pdf
 
Alternatively you can go flat enough to stay inside the circle
@TedShifrin circle is of radius 1, so that's 2 units down 2 units up, 4 in total!
 
3:47 AM
Far from done ...
 
That's close to 4 and I don't have paper near by
I miss analysis and things you can draw (cough math.stackexchange.com/questions/1000606/… )
So @KajHansen what other analysis books do you own?
 
@AlecTeal, not many. I'm a big algebra fan. Analysis...not so much. I have Rudin's PMA and Real & Complex Analysis, Lay's Analysis with an Introduction to Proof, Ted's book (if one considers that analysis), and Spivak's book (again, if that's considered analysis).

I'm probably missing some - my dad has an extensive math library back at home that is slowly becoming my own. :P
 
@KajHansen A first course in Real Analysis is missing - by Protter and Morrey
 
I've actually never heard of it. But I'm sure I can find a copy in the library tomorrow afternoon.
 
I also don't like Rudin's real and complex analysis much, still no clue what PMA is
 
3:57 AM
PMA = Principles of Mathematical Analysis. I.e. "Baby Rudin"
 
Baby Rudin?
Stop making up terms! That is a good book, small but filled with useful stuff!
 
The one with the blue cover.
Making up terms? LOL
@TedShifrin, what did you say was your favorite intro Analysis book?
 
@AlecTeal You're usually really aggressive Alex. Chill.
 
@PedroTamaroff how dare you say that! :P
But seriously "Baby Rudin?"
 
@AlecTeal Google "Baby Rudin." You'll get a lot of hits.
 
4:03 AM
But anyway I like Lang!
 
Oh man, Lang has written so many books.
 
@KajHansen Yes. Scared off Bourbaki.
 
I didn't even know he wrote an analysis text.
 
Also, Kaj, note that in the completion you have, if you got any class $x=[(x_1,x_2,\ldots)]$, then for $x_n^\ast=[(x_n,x_n,\ldots)]$, $x_n^\ast\to x$.
That is pretty useful for proving the thing is complete.
 
Thanks for the advice @Pedro!
 
4:07 AM
@PedroTamaroff I'll try and dial down my aggressiveness, seriously.
If I wasn't I'd be like "lol pussy", but you're not the first to say that.
 
@AlecTeal, what part of your math career are you in?
 
Denial probably.
 
LOL
I meant, like, undergrad/grad student, etc
 
Stuck with manifolds
Night guys
Also seriously math.stackexchange.com/questions/1000606/… I just got a comment and I was like "finally, guidance" but it was to something else!
Nighty night
Just go +10 rep, not from that though
 
4:28 AM
Gotta love accepted answers with 0 upvotes. :P
 
Heh
 
4:42 AM
Hey @KajHansen, I'm a UGA student as well
 
Woah! That's awesome @Zach. Undergrad or grad student?
 
undergrad, 2nd year
CS major
hang around here to try and learn and get help when I need it :P
 
What a coincidence. I see you're a user on StackOverflow. What brought you to the math SE?
 
I love certain types of math and need help sometimes for my math class, like I said :P
 
How did user Carebear->Weapon of Choice->just a brick in the wall change his name so quickly?
 
4:46 AM
Ah, I see now. That's awesome though. I love seeing people I know on here.
Or people I'm very geographically close to I should say :P
 
Happy day all!
 
do you ever talk with PeteClark or TedShifrin in person, @Kaj?
 
hahaha, I've had three courses from Ted. I'm taking topology from Dr. Clark next semester. He's subbed for our real analysis lecture a few times too.
 
I had Clark for calc 2 last year
 
4:50 AM
Ted's in the chat here a ton. You just missed him.
 
That is precisely why he asked Kaj
 
Based on the few times I've seen him lecture, I'm looking forward to actually having a class from him.
 
@KajHansen I have talked to him some
I also see Dr. Clark walking around Athens a surprising number of times this semester
 
Were you there for the "all the math you have learnt you have forgotten, I'm shocked!" @Kaj
 
YES!! @Committingtoachallenge. Hippa (or whatever his username is now) nailed the personality.
 
4:53 AM
@Kaj are you any good at cylindrical coordinate problems from calc 3?
 
He is great at them, as am I <3
 
0
Q: Plot Cartesian prism in cylindrical system

Zach SaucierMy objective: Use cylindrical coordinates to find the volume of the prism whose base is the triangle in the xy-plane given by y = 0, x = 1, and y = $\frac{7}{2} x$, and whose top is given by z = 8 - y. In Cartesian coordinates, this is straightforward to me: $\int_{0}^{1}\int_{0}^{7/2x}\in...

I'm terrible at them apparently, haha
 
It's been a while @Zach, but I could probably point you in the right direction, haha. The hard part is usually finding your limits of integration.
 
exactly
 
Yuck. That is definitely not a region I'd be thrilled to use cylindrical coords.
 
4:54 AM
I know right
 
I'd def. just use cartesian. Is it a hw problem or something?
 
Why cylindrical for that?
 
@KajHansen you should be very comfortable with switching coordinate systems
So for the sake of practice!
 
@AlecTeal, sure. But why make life unnecessarily difficult?
 
@KajHansen ya. I mean the hw problem accepts the answer from catesian, I just need to know how to do it for the test
 
4:57 AM
@Zach, that's respectable. Who's your professor btw?
 
@KajHansen if it's difficult, practice
 
Will Kazez. I like him better than Clark to be honest. Clark has more theory and such that was beyond my interest
 
I don't mean learning what dV is in different forms, I mean being able to draw a diagram and derive it.
 
@AlecTeal feel free to help me learn :)
 
No, you have to want it and ask, don't be rude.
 
4:58 AM
sorry, didn't mean to be
I posted my question already
 
I don't think there's any intentional impoliteness @Alec, lol
 
Alec is always like this :P
He gets in ludicrous arguments with children sometimes, even though he should know it is pointless(with UserX)
Hey @skull
 
Hi pal :D
 
so, any pointers for converting to cylindrical?
 
I just found out that New Zealand has a rugby team called the Kiwis?
 
5:18 AM
I would believe it, but I don't know any teams from NZ other than The all blacks
 
@TedShifrin Sorry, was away. How'd you get those coordinates?
 
5:59 AM
@Committingtoachallenge are you there? :)
 
6:39 AM
@Committingtoachallenge I was wondering where you got the list from. I did some research on each of the books and they seem to be incredible resources. I posted the list on my facebook, so that's enough to keep me honest.
 
6:53 AM
Hi people
 
@UserX Hello.
 
I'll probably LaTeX the problems I remember from the contest if anyone's interested
In about 3 hours or so
 
7:39 AM
Hi
 
 
1 hour later…
8:59 AM
Greetings
 
rAm
Hi
 
1)find $a \in \Bbb R$ such that $x^2-(3a+5)x+186$ crosses the x-axis at two distinct points with integer coordinates.

2)solve;
$$x^4+x^2y^2+y^4=91$$
$$x^2+xy+y^2=13$$
4)Find all $n$ that have exactly $4$ positive divisors such that $d_1<d_2<d_3<d_4$ and
$d_1+d_2+d_3+d_4=640$
3 was a geometric problem that I can't translate
 
rAm
is there who can help me in under standing the word Problems?? actually preparing for a test ..
 
Any takers?
 
9:02 AM
@robjohn did you see the last question I posted on main? (it's really enjoyable)
7
Q: An integral by O. Furdui $\int_0^1 \log^2(\sqrt{1+x}-\sqrt{1-x}) \ dx$

Chris's sisThe following integral was proposed in a paper by O. Furdui, namely $$\int_0^1 \log^2(\sqrt{1+x}-\sqrt{1-x}) \ dx$$ and then the generalization $$\int_0^1 \log^2(\sqrt[k]{1+x}-\sqrt[k]{1-x}) \ dx$$ As regards the first integral, my approach was to combine the integration by parts and the va...

I wonder if there exists a faster solution than mine ...
I wanna propose a new question (in chat) ...
No, it's too easy ..
 
9:18 AM
@Chris'ssis Did you work out that long question?
$$\int_0^1 \left(\int_0^1 \frac{(x y-x y \log (x)-x y \log (y)+x y \log (x) \log (y)-x+x \log (x)-y+y \log (y)+1) \log (x y+1)}{(1-x) x (1-y) y \log (x) \log (y)} \, dx\right) \, dy$$
 
@Committingtoachallenge This one can be turned into a series about which the math world can do nothing since there are no tools yet to approach it.
10
Q: Evaluation of a tough double integral

Chris's sisThis is an integral coming from personal research, and very important to me, but it does not seem an easy job to do. If a solution is not possible then I'd be glad with a closed form only. $$\int_{[0,1]^2} \frac{(1-x-y+x y+x \log(x)-x y\log(x)+y \log(y)- x y\log(y)+x y\log(x)\log(y))\log(1+x y)}...

 
Ahhh, very sad, was a nice problem
 
9:41 AM
Here is another funny problem by Furdui ...
$$\int_0^{\infty} \int_0^{\infty} \frac{\sin(\alpha x) \sin(\beta y)}{x y (x+y)} \ dx \ dy$$
I'd also created the following version
$$\int_0^{\infty} \int_0^{\infty} \int_0^{\infty} \frac{\sin(\alpha x) \sin(\beta y) \sin(\gamma y)}{x y z (x y+x z+yz)} \ dx \ dy \ dz$$
 
All greek characters are constants?
 
Yeah
 
What does the first evaluate to?
 
For the second one is this a legal solution; By observation, (x,y)=(1,3),(3,1),(-1,-3),(-3,-1), and two ellipses have at most 4 points of intersection. Thus these are all the points.
 
That is a geometric solution, so it is non-rigorous, but would work fine in a geometry class
 
9:51 AM
It's a contest
 
What contest?
 
Math contest :P
 
Was the contest called 'Math Contest'??
 
The contest 3 stages before the olympiad. Anyway, what would be a rigorous solution?
Thales 2014
 
How long would one have to solve such a problem in this contest?
 
10:01 AM
Hey @UserX how much time left?
@Committingtoachallenge It was a law, and not a theorem, and it works my way :P
@UserX Hmm. Lets check.
 
10:47 AM
@Sawarnik what do you mean?
I left at 2 hours, it was a 3 hour exam
I definitely failed
Too much NT that I've never seen before
 
@UserX :/
 
I'd like to report this user
2
His answer is to all homework questions is this:
"Please do not post homework on Internet before you hand them in.
By the way you can come to my office hours (Tuesdays 14-16) if you have difficulty about the course materials.

Sincerely,
Your teacher of Galois theory course"
 
@Nick starred
 
11:08 AM
@Hippalectryon: ... I have never reported a user before so I don't know how things work.
 
@Nick I'm not sure either :)
 
But I'm sure people don't just star it.
lol
@Hippalectryon: So, how are you, TheGame :D
 
Fine, fine, and you ?
 
Sick, Sick and cough
I might be contagious.
 
11:11 AM
@Hippalectryon: You should keep your distance.
 
Done :P
 
Hi everybody.
(Imagine if this were a real room and I walk in)
How many of you are going to run away screaming "ebola!!" ?
 
11:38 AM
Didn't see didn't care
Hey look, a $\therefore$ made out of stars : $\stackrel{\star}{\star \star}$
 
:D
$\huge\stackrel{\circ}{\circ \circ}$
 
Anyone understand what's Did's objection here? math.stackexchange.com/questions/987222/…
 
$$\LaTeX \text{ is good for } \vec{M}4 \tau \mathbb H3 \vec{M} 4 \tau I \mathbb C 5$$
 
@UserX I=1st or 2nd part of the comment ?
 
Both
 
11:45 AM
@UserX: Well, you didn't answer the whole question... I don't frown on your answer, I frown on the predicament.
@UserX: Did's objection is not out of having an actual point but from feeling uncomfortable from your rough method.
 
rough?
 
Well, it's fundamental algebra... something I do in the rough column.
@Did $z^3-i=z^3+i^3$ — UserX 11 mins ago
^ @UserX: Put that in your answer
@UserX: Rough in the sense how "$\int 1/x = \ln x$"
You need to be clearer
$\int \frac{dx}{x} = \ln\left|x\right| + C$
Ah, I suck at analogies
@UserX: Yours is a valid method :D Don't fret
+1 :D
 
Lol anyway, I added it.
 
and hence
43 secs ago, by Nick
+1 :D
@UserX: Do you think I suck at communication?
I think I do.
I constantly fail in trying to express what I mean
For example,
2
Q: Hiding the constant of integration

NickI sometimes find writing and keeping track of the constants of integration a somewhat messy job. Yes, sometimes it's necessary but in many situations that I come across in my level of mathematics, it is a waste of time and space. An exagerated example: $$f''(x) = g''(x)\\ \stackrel{\int\text{in...

 

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