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05:00
yeah it is $(x_1,x_2) \in A_1 \times A_2$ such that $x_1 \in A_1 \ and\ x_2 \in A_2$
which is the same as above
user147690
Yeah so $x\in A_1\times A_2\times \cdots \times A_n$ means that $x$ is an n-tuple
yeah
which is same as mapping definition
yeah good I hate it when I confuse definitions sometimes
user147690
Yeah usually happens when I am tired
yeah exactly
next semester I shouldn't have as much heavy course load though, so it should be good
05:17
what all the topics you have next semester @Karim?
algebraic topology and applied algebra
and electives
cool!!!
actually electives will be super easy
electives include?
I have monday Wednesday and friday off
introduction to economics
lol
05:18
Jeez...
and anthropology
and english
yeah I have been taking 5 hard classes forever
its nice to have 1 semester where its like not too much pressure
wha?? anthropology?? Do you guys even get these kind of subjects?
to graduate
user147690
@Rememberme Elective options usually are out of 50 things
I already took 2
you must take 4 arts electives
like I don't know why I do I even have to take art electives
its stupid
user147690
05:21
@Rememberme You can take the most obscure things
@AlexClark here we are required to take 4 art electives
As much as I know we don't even name arts in our math courses here
user147690
That sucks, we don't have to do any electives or anything
user147690
@Rememberme I don't know what that means haha
I would gladly you know take hard math courses than taking art electives
it sucks
but whatever I will just get easy grade and to hell with it
05:23
Did you guys have a course in higher logic?
user147690
Most people say these easy electives will give them good grades, and then end up having so much trouble motivating themselves to do the work they get worse than normal grades, atleast from my friend group
yeah but it is a science thing
I guess they consider it it here to not to be art
yeah that is exactly it @AlexClark
actually the two arts electives lowered my average
that I took
If I have to chose an elective I will choose psychology if it is there
user147690
Yeah I would only take physics courses as electives or maybe bio or chem as long as they have no practical experiment sessions
@AlexC Hows math going?
user147690
05:27
@Rememberme Doing some boring Cardano method stuff :'(
user147690
@Rememberme Finding roots of cubic polynomials the super boring way
yeah I did that for my science electives @AlexClark
I took chem,computer science,and alot of physics
I wanted to ask you this... Do you have any real analysis problem sheets with you?@AlexC
user147690
@Rememberme From 1.5 years ago yes
Can you email them to me?
user147690
05:29
@Rememberme Sure
If you have topology can you send them also. I am in real need of loads of questions@ALexC
user147690
Got no topology questions really, unless you include functional analysis I
No not functional analysis. I don't know much except measure theory
user147690
You know some measure theory?
user147690
Well the functional analysis 1 was mostly point set topology
05:32
@AlexClark Yup some thanks to rudin
leave that then.
user147690
Like product topology and homeomorphisms and such
user147690
Hausodorff spaces etc
I might be disturbing you right now , sorry@AlexC But a bit of abstract algebra till rings will be good
user147690
@Rememberme Remind me tonight I guess
when precisely?
Time zones... :( that is why
user147690
05:35
Oh my bad different timezones, I should be good to do it in 5 hours or something
user147690
I'm 4.5 hours ahead of you pretty sure, its 3:35pm right now
@AlexClark Oh okay, thanks ! Do you know my email?
user147690
@Rememberme Nope
08:59
@Ted, when you come back: do you know of any other books/sets of course notes besides yours (real expensive here) or Hubbard & Hubbard (apparently you recommend against it) that are nice for multivariable?

I'd greatly prefer one that does differential forms / manifold-y things and such. Yours is basically perfect, from what Balarka says, but, you know, I probably can't justify the price to my parents.
Even pdf course notes are fine.
user174558
09:33
@SohamChowdhury You may want to look at Zorich's Mathematical Analysis I and II.
user147690
@Jasper I personally hate Zorich's mathematical analysis I
user174558
Hello @AlexClark. Why hate it?
user147690
@Jasper I tried it, and after 80 pages I hated it
user174558
What's wrong with it?
user174558
I have been having strange physical symptoms. When I am sleeping my head sometimes jerks violently.
user147690
09:35
@Jasper I can't remember, I think it was a section where it essentially rambled for 20 pages
user174558
There is a new edition coming out next year, with added appendices. I might want to get it.
user174558
It's not epilepsy, but feels quite similar.
user174558
Your blue is as beautiful as mine.
user147690
Sorry was briefly afk. I think this is my favourite identicon(I did try 30 or so, before stopping here)
user174558
30 or so? You are nuts, like me.
user174558
09:44
I think I will retire from the main sites and just come to chat. I think I will keep this account for life.
user174558
@AlexClark After studying Mathematical Logic and Set Theory by O'Leary, I will study Combinatorics and Graph Theory by Harris. These will be my first two books for next year.
user147690
Start studying some commutative algebra with me @Jasper?
10:39
@Jasper uh, I don't really want an analysis book.
I want a pretty book with a lot of pictures in it. :P
11:16
what did I miss?
you don't want to know, @Soham?
Some stuff about people doing sock puppetry @Soham
oh, screw it then.
user147690
@SohamChowdhury Boring drama
I thought it was over a long time ago.
user147690
11:18
@SohamChowdhury Nah, always more
I came back and saw Alec's (removed)s
it's never over.
and got curious
user147690
One of the long term trolls got banned
ah, good then.
user147690
11:18
Oh I didn't mean that (alecs removed messages). I meant Twink/anti-g**/user
Who is the long term troll ?
user147690
What are you working on @SohamChowdhury?
@AlecTeal I have half-proved the theorem you wanted to know the proof of. Do you want to know the progress, or do you want me to ping it to you after I have figured it out?
Hit me.
@AlexClark Bilinear forms
user147690
11:20
@SohamChowdhury Ahh that's right, from Artin
Cool stuff those.. Doing from artin I suppose@Soham?
user147690
@SohamChowdhury Time to learn some Lie algebra then I guess :P
I did a bit from Artin and am now reading them from KCd's notes.
Yeah, pretty excited about getting to all that stuff.
I did from HK
user147690
@Rememberme HK?
11:20
Hoffman-Kunze
What are you upto, @Rem?
user147690
Don't remember it hmm
That's right
Altop, Complex analysis and algebra@Soham
user147690
@Rememberme Did you understand why $[\Bbb Q(\sqrt{2}):\Bbb Q]=2$?
whew, that's a ton of stuff. from where?
Altop, Complex analysis and algebra@Soham
11:22
@Alex high pitched voice me! me! me!
@Rememberme where are you studying from?
and what are you doing at the moment?
Nope . I have too many things at the moment
Munkres, tw gamelin, DF
Respectively
where are you in each?
user147690
@SohamChowdhury Go for it then :D
@AlexClark I meant the Q(\sqrt 2) thing
Currently altop
user147690
11:24
@SohamChowdhury Yeah, why is the degree $2$?
@AlecTeal $f : M \to N$ be a continuous bijection. If $\dim M = \dim N$ : $f$ must be chartwise one-to-one because $f$ is one-to-one itself. By invariance of domain $f$ is open. Open bijective continuous map is a homeomorphism, so you're done. For $\dim M > \dim N$, similar logic : $f$ must be one-to-one chartwise.
So all you have to do is to prove that there is no injective continuous map $\Bbb R^m \to \Bbb R^n$ for $m > n$. Assume there is. Then look at the image of the $(n-1)$-sphere in $\Bbb R^m$ and apply Jordan's theorem. The image disconnects $\Bbb R^n$ (note that the connected compo
Mike hinted at using Baire category for $\dim M < \dim N$, but I have not thought about it yet.
@AlexClark as vector spaces, (1,\sqrt 2) is a basis. that's the defn. of degree, right?
user147690
@SohamChowdhury Correct
user147690
Well more specifically it's a two dimensional $\Bbb Q$-vectorspace(with basis $\{1,\sqrt2\}$)
@soham in munkres deformation retracts, just started holomorphic functions, finishing sylow stuff(I am going particularly slow there)
11:26
I use ordered tuples because I'm a cool guy
user147690
@SohamChowdhury :D you are
well, you have a lot on your plate, @Rem.
user147690
@Rememberme Why is there no simple group of order $150$?
@Alex is getting all Balarka-y with his questions
user147690
@SohamChowdhury I have waited long enough :P
user147690
11:27
It's been my dream
I guess something to do with prime factorizations or something? I skipped chapter 7 of Artin :(
@AlexC that us why I said . I am slow there. I have to do it again. I left sylow theory in middle(towards the end) so cant answer your question
user147690
@SohamChowdhury Sylow theory, which he said he was finishing
mmm.
the plot thickens
user174558
@SohamChowdhury Nice pic.
11:28
What are you guys discussing about?
But currently working on a balarka question. I really need his help on it. @Balarka
@AlexClark Because the order is not divisible by $4$ of course :)
user147690
@BalarkaSen I'm giving then questions :D
It's getting kind of weird because I'm ignoring Sayan. Maybe I'll unignore him after all.
user147690
@BalarkaSen What why? Oh. I thought you said Soham and was like WTF
11:29
Pls help me with the center of the fundamental group question @BalarkaSen
Ya!!!!!
user174558
I see the user and Twink chat accounts have been suspended.
because he's doing too much stuff and messing it up in the process, like I used to do?
Thanks for the Diwali gift @Balarka :P
@Soham No, because he googles every single question I give him and claims he cooked it up himself.
@Balarka, @Alex if $R_B : v \to B(-, v)$:
11:30
Reasons @Soham explain you in an email
user174558
@BalarkaSen must be up to no good with that gift.
how do I do the line for partial application in LaTeX?
user147690
What sort of line is it?
Not every one :P
user147690
$B(-,-)$
11:31
@Soham $B(-, v)$
Okay, now formally. Sorry @Balarka
user147690
@BalarkaSen Wink to you too
never knew that works.
anyway, look at this:
Huy
Huy
@Soham long time no see
11:32
@Huy aye, indeed.
I remember @Soham once said Bilinear forma looked liked smilies
@BalarkaSen if we have limsup of $\frac{x+a}{x+b} sin^2(\frac{1}{x})$ where a and b are real numbers$ then should I first find the sup of the fraction and sin part?
user174558
It is Diwali here too. I was reading how Hinduism is not really a religion but a collection of practices.
why would $L_B$ (defined in the obvious way) not work?
would that give the transpose, like I think?
@Paradox101 I don't want to think about real analysis, Paradox. Why don't you ask Daniel Fischer?
11:33
Nicely said @Jasper
@Remember Remind me what the center problem was.
@BalarkaSen ok
user147690
@SohamChowdhury What page is this? I am not familiar with any of it(atleast in this form)
@Huy can you let me know that if we have limsup of $\frac{x+a}{x+b} sin^2(\frac{1}{x})$ where a and b are real numbers$ then should I first find the sup of the fraction and sin part?
user174558
@AlexClark I think atleast should be at least.
11:34
Something self-homotopy equivlence, something something image of $\{x_0\} \times I$ being in the center.
Jasper speaks the truth.
user174558
Buddha speaks the truth.
@Jasper technically true, but the majority of Hindus believe a lot of very similar things. i.e. it's more uniform, in practice, than what that statement would have one believe
I have to run now. Sorry @Balarka leaving the question. I am also on my phone so I will come with the whole question on altop chat
@AlexClark this isn't Artin.
11:35
ok.
Balarka, any help?
what's the question?
saw the screenshot?
user174558
@SohamChowdhury I currently do not subscribe to any religion except Theravada Buddhism.
11:36
I'm checking if using $L_B$ instead of $R_B$ would give the transpose of the correct matrix.
You're losing me with notations. What's $L_B$?
@Jasper that's nice, but where does that follow from?
arrey it's like Hom functors
$L_B: v\mapsto B(v,-)$
$R_B:v\mapsto B(-,v)$
OK. So you're checking if the matrices for these two are transposes of each other?
user174558
@SohamChowdhury Nowhere.
11:38
of course, respective to a given basis of $V$ and its corresponding dual basis for $V^{\wedge}$
i was banned in another room for speaking religious stuff and now they are discussing it openly, dont really know how people's mind work, i just avoid to get stuck in a clash of cultures henceforth.
Gotcha. So is that the question?
that is my question, yes.
why would not $L_B$ work?
my answer is that it would give the transposed matrix.
Are you sure it'd give me the transpose? Because I haven't checked.
because $L_B(e_j)(e_i) = B(e_j,e_i)$ whereas $R_B(e_j)(e_i) = B(e_i,e_j)$
looks like transpose to me.
I actually came up with the answer just after asking you guys. this happens too much :P
11:41
That seems fair.
I agree with you.
I mean, of course - since $L_B(v)(w) = B(v, w)$ and $R_B(w)(v) = B(w, v)$, these two maps are transpose of each other, hence so are the matrices :P
I wasn't paying attention.
once you parse all the notation, it's essentially obvious.
mhm.
oh, by the way, have you read the proof of Cayley-Hamilton theorem from Artin? That's something which comes up in module theory/commutative algebra in a much more enhanced and powerful form - namely, Nakayama's lemma.
the proof felt like cheating, actually :P
"we won't have distinct eigenvalues (generally), but we can get a convergent sequence all of whose elements do"
it's a beautiful proof.
@SohamChowdhury Does that work in the usual topology, or does he use the Zariski topology?
11:49
@TobiasKildetoft Artin proves it over $\Bbb R$.
no, the best proof is "subsitute $t=A$ into the expression $\det (tI-A)$, haha
(I know that doesn't work)
@BalarkaSen Ahh. Same proof works over any field (or even integral domain, not sure if it can be extended to all rings)
@TobiasKildetoft Really? How so?
@BalarkaSen Embed into an algebraically closed field to reduce to the case of such
the note that the set of matrices with distinct eigenvalues is open in the Zariski topology and hence dense
oh wow
11:52
(it is given by the non-vanishing of the discriminant of $det(A - \lambda I)$)
and since the statement is easy to show for these matrices (being diagonalizable), it follows
that is very slick.
(using that affine varieties are separable, so if a morphism is $0$ on a dense set, it is $0$ everywhere)
correct me if i I'm wrong.
this hinges on the fact that for (2), diagonal entries have to be zero unless your field has characteristic 2.
yes
skew-symmetric matrices have diagonal entries = 0 : you need to have $a + a = 0$, clearly impossible for nonzero $a$ if you're not in char 2 field.
Just a really simple question
11:57
that's what I thought.
is the function f(n) = n^3 surjective over the domain of all integers?
i.e $\mathbb{Z}$
@cp101020304 with what codomain?
f is a function from integers to integers? then no.
2 is not a cube of any integer.
from Z->Z sorry i should have specified
@BalarkaSen thank you sir
ei, @Balarka.
12:02
How do I prove that a function is uniformly continuous if the function in question is written in terms of the integral of another function which is riemann integrable?
does the space of all (nondegenerate) bilinear forms on $V$ have any structure?
subgroup of $GL_n$?
i.e. $GL_n/(A\sim B$ if $P^tAP = B$ for some $P)$
is that a group?
@SohamChowdhury to each billinear form $V \times V \to k$, you can associate a linear map $V \otimes V \to k$.
ohhh
$\text{Hom}(V\otimes V,k)$?
\otimes.
yes.
so symmetric 2-forms on $V$ ;)
12:08
2-forms as in . . . differential forms?
and why symmetric?
yes. but these are symmetric.
wedge is antisymmetric.
$a \otimes b = b \otimes a$, but $a \wedge b = - b\wedge a$
@BalarkaSen $\otimes$ is not symmetric
I thought you couldn't do that
a \otimes b is just that. you can't flip them.
(AFAIK, of course)
my internet is horrendous, sorry
@TobiasKildetoft yikes! I was thinking of symmetric tensors. of course not.
ok, better name?
Not sure I have seen a notation for elements of a symmetric power
12:15
unsymmetrized forms, maybe?
meh, who cares. it's just $\hat{V} \otimes \hat{V}$.
Huy
Huy
@Paradox101: But the limsup of the fraction is $\infty$
darn this internet connection.
@SohamChowdhury Yes, you are right, I am being silly. Confusing with symmetrized tensor products, where $M \otimes N$ is defined by qt. of the free module on $M \times N$ by the usual billinear relations + $a \otimes b - b \otimes a = 0$
Of course, in general, tensor products need not satisfy that last thing.
@Huy yes but if I rewrite the fraction in terms of two fractions which are being added and multiply them with the sin part won't that make things easier?
Huy
Huy
@Paradox101: can you specify what you exactly want to do?
Also can you explain that given a function how do I prove that it's uniformly continuous if the function in question is written in terms of the integral of another function which is riemann integrable? I tried writing it in terms of |g(t)-g(s)|< $\epsilon$ but then that reduces to epsilon is greater than zero
Is this correct @Huy ?
Huy
Huy
12:48
@Paradox101: sorry, but "limsup" can be anything. you need to specify what lim sup
That isn't specified in the question @Huy
Huy
Huy
then it's not a well defined question
I can't expect my students to find $\lim \frac{1}{n}$
All that's meniond is that a and b are real numbers
Huy
Huy
that question doesn't make any sense
yes
but if for instance i was x approaches infinity what would it be? For x approaches ?@Huy
Huy
Huy
12:51
$0$ I think, but I might be wrong
@Huy how will you get $0$?
Huy
Huy
the sin part is 0 and the other part is a constant
I mean if we just take the sup of the function then it should be 1 no?
the sin part
no sinning pls
says who?
12:59
Me
A cat
A well-behaved cat
Huy
Huy
but as $x \to \infty$, $\sin(1/x)$ doesn't oscillate anymore
it just gets smaller
@Huy small but mighty
@Huy ok but then what function does sup serve?
Huy
Huy
if you take $\limsup_{x \to \infty} \sin(x)$, then you get $1$
even though $\lim_{x \to \infty} \sin x$ doesn't exist
@BalarkaSen reading "free module" as "vector space", that agrees with what I know
13:02
:O
welcome back @SohamChowdhury
I took a break.
actually no more math tonight, probably. I have to study physics.
that can be the same thing :P
@Huy but in this context if we take only the sup of the function what should be the right answer?
Huy
Huy
13:07
What sup
you need to specify
@0celo7 that would make you a cool cat
@Huy but don't we need to specify what x approaches to for the limit? Shouldn't we be able to simply take the supremum of the function?
Say $m$ is a positive even integer. Then find $$m+\frac{1-m^2}{3!}+\frac{(3-m^2)(1-m^2)}{5!}+\frac{(5-m^2)(3-m^2)(1-m^2)}{7!}+‌​\cdots $$
Huy
Huy
@Paradox101: if you take the sup of a function $f(x)$ you need to specify what $x$-values exactly we are allowed to use
it doesn't make sense to write $\sup f(x)$
only something like $\sup_{x \in D} f(x)$ where $D \subseteq \mathbb{R}$ makes sense
@robjohn @r9m see the one above, it's fun. :-)
13:12
@Huy ok. So then in this case if x tends to $0$ the limsup won't exist?
Huy
Huy
why not?
@Huy because sin^2 of infinity isn't defined?
Huy
Huy
$\lim_{x \to \infty} f(x)$ doesn't mean "we plug in $\infty$ for $x$"
I just told you before that $\limsup_{x \to \infty} \sin(x) = 1$
@Huy but in this case it's $\limsup_{x \to \0} \sin(\frac{1}{x}) = 1$
Huy
Huy
so?
13:17
So then as x tends to zero, x inverse tends to infinity
Huy
Huy
$1$ isn't quite "doesn't exist"
yes sorry i forgot to erase that
$$\lim_{m\to2}\left(m+\frac{1-m^2}{3\cdot 3!}+\frac{(3-m^2)(1-m^2)}{5\cdot 5!}+\frac{(5-m^2)(3-m^2)(1-m^2)}{7\cdot 7!}+‌​\cdots\right)=\frac{\pi}{2}$$
@Chris'ssistheartist do we need the limit?
@robjohn No, just a way of posing things is a nicer way.
13:34
If we are given the above function, how do I prove that g is differentiable? Can I state that by using FTC 1 we can say that g is an antiderivative of f?
Huy
Huy
$g(x) = |x|$ is the antiderivative of $f(x) = \operatorname{sgn}(x)$ but $g(x)$ is not differentiable
@Huy then how do we show that it is differentiable? We don't know whether f is continuous
13:56
In this case the derivative of g(x)= F'(x+c)-F'(x-c)?
Huy
Huy
14:08
if you don't know that $f$ is continuous, then that function isn't necessarily differentiable, as my example shows
so then do we use mean value theorem? @Huy
So i can say that g(x)=F(x+c)-F(x-c)
Huy
Huy
???
@Huy i'm just trying to prove that g is differentiable.since I can't figure it out using FTC I thought to maybe manipulate mean value theorem?
Huy
Huy
but $g$ isn't differentiable if you don't at least assume $f$ to be continuous
so then assunming that f is continuous is the only way to prove the differentiability of g?
r9m
r9m
14:36
@Chris'ssistheartist I don't know .. tried it for a while though (can't see anything) .. :) However you might like $\displaystyle m+\frac{1-m^2}{3!!}+\frac{(3-m^2)(1-m^2)}{5!!}+\frac{(5-m^2)(3-m^2)(1-m^2)}{7!!}‌​+‌​\cdots $ .. turned out to be interesting when I was trying to deal with your sum :)
I was trying to turn it into a hypergeometric series but I think I'm too tired to see it, I got stuck here: $$m+{{\Gamma\left(-{{m^2}\over{2}}\right)\,\sum_{n=0
}^{\infty }{{{\left(1+2\,n-m^2\right)\,\Gamma\left(2\,n-m^2\right)
}\over{2^{n}\,\Gamma\left(n-{{m^2}\over{2}}\right)\,\Gamma\left(4+2
\,n\right)}}}}\over{\Gamma\left(-m^2\right)}}$$
r9m
r9m
Holy cow! .. turning it Hypergeometric is the last thing I wanna try! (I'm severely allergic to that thing ,, )
r9m
r9m
14:56
BBL
r9m
r9m
@Chris'ssistheartist hey (I was about to leave for dinner .. ) :) maybe give me some hint to think about while I crunch my fries (over dinner) :-)
@r9m Hey! I'm in trouble with installing a latex file, d*mn. I do all perfectly.
@MickLH Nice that thing! :-)
@r9m It has a nice form?
r9m
r9m
@Chris'ssistheartist ya! That thing telescopes :D (found it while I was trying to make your series telescope into something)

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