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07:00
Wtf
I could have sworn that was a linear map
What is going on
Oh no...
@Anthony You didn't define it over a basis!
It has to collapse it.
@Anthony Any linear maps between two finite-dim real vector spaces will be continuous (when you endow them with the induced real topologies)
But consider yours: $\phi(v) = 1, \phi(v+\varepsilon v') = 0$
Only understood like 1/2 that sentence.
Sorry.
07:01
Nonono I meant to say lol
In any case, does defining over a basis just ensure that it is linear?
Are you cool with metric spaces?
Yeah
I think I get it.
I mean, I see why my map blows.
Ignore my topology nonsense. Just think of what I said as "A linear map $\Bbb R^n \rightarrow \Bbb R$ is continuous"
Hellooooo
But clearly it's not continuous for your map with $n>1$ (just move $v$ a teeny bit and it maps to $0$)
07:03
@JessyCat Hello. They say bunnies and cats get along well.
Beware usukidoll.
I'm kind of a weird cat, though
Keeps pulling and wiggling ears.
I know someone named Jesse.
She cray cray.
Thanks
Yeah. @Mike, so we just define the map by how it operates on the basis vectors, like normal. I feel like there should be another way, but I guess it would be less concrete.
07:04
@JessyCat I thought you were a girl.
I am a girl
@Anthony Nope, that's exactly the one you want.
I mean.
@Anthony Wanna learn a fancy word?
You have another choice... once you take functional analysis.
Predual.
07:05
Oo.
lol
It's just all a tautology.
All of math.
@Anthony Well, yes.
That's the fun part of it.
So is your face, come to think of it
Tautologically so.
You stuff stuff with stuff. But the stuff is the same stuff. Yet the stuffed stuff keeps growing.
It's fun.
07:06
My prof is just kind of assuming we already know functional analysis...
lol
Thanks guys.
@JessyCat Is your proof invoking Hahn-Banach?
That's my proof.
@JessyCat You'll like Mike.
He also likes to complain.
Oh.
Prof, not proof.
No, Banach-Alaoglu
And he also assumes we all know about manifolds. Hehehe
It's fun
07:08
What did he invoke BA for?
What class is this?
@Mike weak* was $x_n\to x$ iff $\varphi x_n\to\varphi x$ for every $\varphi$ ya?
We were proving some Sobolev-type inequalities
@PedroTamaroff "Initial topology" better?
It's called Analysis II. It's a grad class
@Mike The initial topology on the functionals. Right.
@JessyCat Hehe. My "Analysis II" class is integration and ODEs.
07:09
Weak* is just another word for initial.
Our analysis 2 is boring stuff
The prof wants me to take it. Lolno.
And by integration I mean Stokes', Gauss, line integrals yadda yadda
Wanna trade? LOL
@JessyCat Your course is cool.
Keep it.
I'm constantly stressed!
@PedroTamaroff My analysis 2 prof is like "Oh, we'll be doing measure theory! You should take that!"
07:10
Sillypantalones.
Lolnoooooo
@JessyCat Why?
Measure theory's awesome if it's taught right.
I agree
I've just taken it essentially 3 times now
I'm not taking it for a fourth
@Pedro, b/c I don't think I have sufficient background
07:11
@JessyCat Read extra material! =D
Pedro, I am! It's just hard to know what holes I need to fill in...
Ah, so the opposite of @PedroTamaroff's problem
@JessyCat Every hole! Every hole!
@PedroTamaroff Gross, dude
@Mike You're the one with a fucked up imagination.
07:13
Yeah. I've been stressing for 9 days about this problem I posted. The only person who commented told me something not terribly useful.
That dude you pinged earlier, I hope he can and is willing to help!
What the hell is that?? LOL
@JessyCat Who?
Watch the ground after the ceilings collapse.
@P
Ask Jonas! =D
07:15
I pinged Daniel
@JessyCat Can I see the course topics for your course? I'm interested
If I knew them myself, I'd tell you. We didn't get a syllabus.
Ouch.
Nor is there any kind of official textbook
@Mike You don't know Jonas.
He's a cool guy.
What if I told you I was Jonas?
07:20
I'd laugh sarcastically.
He's my analysis alter ego.
On the first day though, he did tell us essentially what we'd be doing: 1) Variationsl Metgods: gradient estimates, weak compactness. 2) Regukarity Tgeory: maximum principle, DeGiorgi-Nash-Noser Theorem. 3) Model equations: equation of constant scalar curvature of surfaces, geometric flows (heat equation).
Flows? Interesting
That doesn't seem like a standard analysis class topic, that's solidly geometry
So basically, functional analysis applied to PDEs. Most if the people in my class went to really good undergrad schools, so they've probably seen a lot of this before.
I think differential geometry or analytic geometry might be his area if research?
Are you training to be an analyst?
07:22
So far, absolutely nothing us standard about this class! But, I'm chugging along.
@Mike Excited.
@PedroTamaroff Have you taken any topology yet?
Maybe you'll be a geometer.
Mike, well that's the plan. My masters thesis was on operator theory. I likes my analysis.
Ah, I see.
@Mike I know a little of topology. Read an introductory text, and I will read Bourbaki or/and Willard when done with Algebra.
07:23
Well, I can't help, then. You need a professional.
I doubt that, but stranger things have happened.
@JessyCat High fives.
@JessyCat I mean, a therapist.
What is $W_0^{1,p}$?
@Pedro, huh?
07:24
@Mike I've been told the topology course in my uni is over master's level.
@Mike, already got one ;P
So I go that going for me.
@JessyCat Er, that.
I don't know what it stands for.
Pedro, it's a Sobolev space, means has one continuous derivative in the Lp norm and it has compact support
@PedroTamaroff Once-differentiable, $p$-integrable functions whose derivative is also $p$-integrable
Once continuously*
Sobolev stuff is important.
@JessyCat Cool.
07:26
Yeah, if math were anything like Catholicism, he'd be a saint.
Him and Cauchy
The norm on a Sobolev space is defined analogously to the $p$-norm: take the $p$-norm of all of the derivatives, and then sum the $p$th power of these norms and take the $p$th root
Only three paragraphs. Sad. =/
I should do more Hungerford exercises.
Sum or integral?
I'm talking finite $k$ here
So sum
I used Hungerford's Abstract Algebra text when I got my masters.
07:28
@Mike Hungerford's 3,4 is Lang's approach.
Oh, ok @Mike.
Finite positive integral $k$
I don't know anything about non-integer $k$ Sobolev spaces.
@JessyCat Cool, point for you on Mike's score! =)
Okay...
@PedroTamaroff what do you mean 3,4? Rings and modules?
07:29
No, exercises 3 and 4 in page 82.
I should sleep
Darn. Byes.
Sleep is for the weak.
Whoa, that was sudden
Yeah...
So, tell me about yourself
You're pursuing a PhD?
The weak and the oks
@Mike, kind of.
Go on (if you're willing.)
07:31
I'm sort of trying to get in through the back door...
So right now, I'm just taking ckasses
Gotcha
Wild bizare guess: are you French?
I'm actually not registered for this one for a grade, though, b/c I didn't think I'm ready for it. Last semester, I took Analysis & Probability I (yes, they combined them into one course; stupid idea) and got an A-
French ancestry, but I'm from the good ok US of A
Good ol, damn auticorrect
For some reason I thought you were French... who knows why
Never works when you need it
Wouldn't that just be measure theory?
07:35
Maybe b/c I'm awake at this unholy hour.
I'm always up at this unholy hour
Essentially, if it's taught right. But our prof taught it like it was a prob theory course
I don't personally understand the difference between probability theory and measure theory (on spaces of finite measure)
But this is because I am an ignoramus.
10 years ago I could do that. I'm about 10 years older than the average grad student.
In probability theory, you're dealing with probability spaces, so everything integrates to 1.
I thought that just meant $\mu(X) = 1$
07:38
@Jessy Cat: I'm nontraditional student too! (Not grad, yet though)
So that you can reduce anything about finite measure spaces to something about probability spaces by multiplying by scalars.
And you say "almost surely" instead of "almost everywhere"
So it's the same shit with different words.
@Mike, yeah, but it can be tricky to "translate@
There's an easy solution to that problem.
07:39
@5space, ^5! Those whippersnappers don't know NOTHIN!
@Mike, yeah? What's that?
Don't bother translating. ;D
Not too shabby.
I gots to get to sleep, though. I have to wake up in 2 hours to get to class. I've got to catch the bus into the city at 7:30.
Ouch...
Yeah...
Anyway, it was nice talking to you! Tell Daniel to get his butt over to that problem ;P
G'nite
night :)
08:25
@PedroTamaroff why u awake
@Mike Hehe.
I took a shower.
Now I won't sleep.
Welcome to my world.
I was looking at dis.
@Mike The Klein group is presented as $\langle a,b\mid a^2,b^2,(ab)^2\rangle$
The 4-group?
08:40
OK, I agree.
You probably cannot see the question now since the OP deleted it.
09:10
@PedroTamaroff Irony zone?
:<
yass
@KarlKronenfelf in da haus?
@PedroTamaroff I'm an elf now?
idgi
09:20
@KarlKronenfeld huh
huh huh
KarlKronenf elf
OH didn't catch that
Oh shit dude.
I was going to write Kaaaaaaaaaaaaaaaaaaaaaarl
I've been thinking your name was Kronefeld this whole time
09:21
But that 'dn't ping you
Kronenfeld.
I realize now.
:confus:
will brew coffee
I want a coffee maker.
@Mike Holy shit, I thought your name was mi
Damn that tab completion
It's an easy mistake.
09:24
@Mike Well, honestly, it may as well be. This is just a pseudonym, in case you didn't know.
I did not.
That explains why it's been so hard to send hitmen after you.
Now that I think of it, Mike's not my real name either
lolwut "now that I think of it"
I don't always remember that
09:31
So you get into this identity. I always have to force myself into a separate internet persona.
No, Mike's just my middle name.
:P
@Mike That I knew.
@AlexYoucis is in da haus.
your first name starts with an s
Noooo
@KarlKronenfeld What if my first name is S?
09:32
Always a possibility.
@Mike You're mexican?
Ese.
Your first name would be Harry Truman's middle name then, @Mike
He was always a funny guy.
I like my middle name.
For several reasons.
I bet it's something weird
Like "Mike"
09:36
It keeps in Russian tune.
First letter is N, @Mike.
So my initals are PNT.
I'd immediately change my name if those were my initials
I wouldn't, I'm kidding
@KarlKronenfeld maybe just nikolas
09:38
Da.
fucker
Nicolás, actually.
yesssss
I win
I should change my username.
@Mike I had an accent, you just can't see it. So we tie.
09:39
Nikolai Tamarov sounds russian math serious stuff.
A friend of mine has the initials RAW
cool.
I fucking hate Coke ads.
Darn it.
I hate all things.
A friend of mine had APE as initials, he was not a very clever man.
I know someone whose initials are SAM
His first name is Samuel
His parents did that on purpose.
09:41
[Sawry mike]
[I forgive]
@Mike Hehe.
@PedroTamaroff Hey.
@Mike If he was a girl, then Tammy
09:43
if he was a superhero, then charles
If his parents were cool, then Ben.
@AlexYoucis Hey there.
@Mike Think I'm gonna skip KS.
@PedroTamaroff You'll learn it when you're doing modules anyway
It's really not very hard tho.
@PedroTamaroff I upvoted T.'s
09:47
It's kinda long, but not hard.
It's like 3 pages.
@PedroTamaroff krull-schmidt?
I like doing it for groups because that motivates it for modules.
Krull Schmidt? Well, it has some previous lemmas.
But the proof itself is one page long, I think.
Fitting's lemma is cool.
I know it from Linear Algebra.
I have never used Krull Schmidt in my entire life.
09:48
Do you need to use it to find it neat?
There is only one theorem in math, or so I think.
Secretly, there are no theorems in math.
You're all about secrets.
Secretly, that's true, but only when interpreted using a decoder ring...a secret decoder ring.
A universal decoder ring
Hint: the theorem is ovaltine.
09:52
A bijection of the set that contains all sets $U$
There's a cat outside that has been screaming for over an hour
It is impossible to sleep until that thing shuts up
Sleep is for those that
don't have enough
Youtube videos to watch
@AlexYoucis Dude.
Hit us with some cool music.
You can't handle my 'zak.
Come on.
@PedroTamaroff Semi-NSFW (I'll delete it once you have the link)
09:57
Done
It's not safe to listen to such terrible music at work.
@Mike I heard LA is wonderful this time of the year.
@Mike Good. They arrived... evil grin
I didn't plant that cat or anything eyes dart back and forth
10:04
@PedroTamaroff Do you speak any Portugese/
@AlexYoucis I can usually understand written stuff.
Since it is pretty similar to Spanish.
Hi, someone can explain me hagen's answer here :http://math.stackexchange.com/questions/681051/convergence-of-a-sequence-with-x-n2-is-non-increasing
I don't understand why if M is finite then all $x_n$ have the same sign? thanks
@Nico He says almost all. This is because $M$ represents the set of all "sign changes".
@KarlKronenfeld I have understand what is it M but not why the hypothesis : finite
10:18
@AlexYoucis Cool.
@AlexYoucis youtube.com/watch?v=G7g11ViJnU0 love that song
RCP is good, but the vocals are the same in every song.
@PedroTamaroff See if you can back this: youtube.com/watch?v=p2qgEl4KWB4
back?
what do you mean?
@PedroTamaroff Back, as in "get behind".
@DanielFischer Sup man.
10:21
The Daniel-o-mann.
I did not understand the hypothesis finite *
Greetings
@robjohn have you ever met this integral before? $$\int_0^1 \int_{y}^{1} y\left\{\frac{x}{y}\right\}\left\{\frac{1}{x}\right\} \ dx \ dy$$ I'm still working on the triple version and wonder if here there might be found a nice way here.
@AlexYoucis Hi, nothing much. Trying to get the system up and running, needs moar tea.
10:36
@robjohn I think I missed and alternative way of writing $\displaystyle y\left\{\frac{x}{y}\right\}$
That's it!
Back to work.
@Chris'ssis I looked a bit at that problem but nothing jumped out at me, and then I got distracted by other things. Sorry :-)
@robjohn OK. The integral above is pretty evil too.
@Chris'ssis do you know what it evaluates to?
@robjohn I will know soon.
@robjohn Oh, another idea came to mind. Let me try it.
10:51
@DanielFischer What is a nonabelian group of order 15?
@PedroTamaroff Impossible?
That's what I thought, yes.
Because by Sylow, $G$ is $\simeq P_3\times P_5$.
So $G$ is $C_3\times C_5$.
So every group of order $15$ is cyclic.
And non-abelian cyclic groups are rare.
If only the empty set had an identity element.
11:24
Hi @TedShifrin
11:49
@robjohn I'm so happy here!!! I found a brilliant way for that integral! :-)
12:01
@Chris'ssis what did you find?
two users were removed this morning?
@robjohn I think there was some mistake that simplified things a lot. I need to retake all :-(
I need to dig up some more. (however there is something I have but I need to recheck it a bit)
$$\int_0^1 \int_{y}^{1} y\left\{\frac{x}{y}\right\}\left\{\frac{1}{x}\right\} \ dx \ dy=\int_0^1x(1-x) \left\{\frac{1}{x}\right\} \ dx$$
12:25
Heya
@robjohn ?
@N3buchadnezzar howdy
Solving the integral from this answer http://math.stackexchange.com/a/558148/18908 gives me
\begin{align*}
= \frac{\log (2a^2)}{a} \bigl[ \arctan n + \arctan m\bigr]
\end{align*}
Whie the correct answer is
\begin{align*}
I_1 & = \int_{nm}^{na} \frac{ \log(x - a) }{x^2 + a^2 }
= \frac{\log (2a^2)}{a^2} \bigl[ \arctan n + \arctan m\bigr]
\end{align*}
@robjohn Can you spot my mistake?
13:02
@N3buchadnezzar let me look
 
1 hour later…
14:13
Hello all! Let's assume that we have an $n$-dimensional Gaussian distribution with pdf $f(\mathbf{x})$. And let $H$ an $n$-dimensional hyperplane. What is the mean distance of some point in $\mathbb{R}^n$ from the hyperplane? Thanks!
14:45
@robjohn I finally put the monster in knees. It's simply down. Could you check pls some of my work while working on the last part (meaning to put on paper the details)? Now or later ... as you want.
@Chris'ssis Anything new on series?
@BalarkaSen there are always new things. I put some monsters on knees. :-)
@Chris'ssis I don't understand that expression.
@BalarkaSen I mean they are down. :-)
@Chris'ssis Oh, okay. Toxicated English. Where are you from?
14:56
@BalarkaSen Romania
@Chris'ssis Hmm.

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