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11:00 PM
yes, and it's even true without the $\det$
 
Sure, @chandx, because $(F(V),F(W)) = m(F)\cdot (V,W)$.
 
:P
 
Assuming you're using the same basis to express everything in coordinates.
 
@TedShifrin So I gave $S^n$ a cell structure which makes it into a CW complex using the definition of a CW Complex as a Hausdorff space with a cell decomposition (that satisfies some other conditions), but using that cell structure I can't build $S^n$ up inductively (which is the other defn of a CW Complex) since it's $n-1$ skeleton is empty
 
Leaky beat me because I typed it out.
 
11:00 PM
Hope that clears it up
 
If $A \leq G$ and $B \leq H$ then $A \wr B \leq G \wr H$?
 
and also you don't need $V$ and $W$ to be linearly independent
 
@LeakyNun I don't think the attaching maps make sense then
 
Sure you can, @Perturb.
The attaching map can go to a lower skeleton.
 
lol, okay so it's just matrix multiplication
thats why it holds
 
11:01 PM
After all, the lower skeleton is a subset of a higher skeleton.
Yup, @chandx.
 
Ted the sign is just from this derivative property d(-f)=-df
 
Yes, @Manolis, of course.
Or, if you think geometrically, principal curvature is positive if the normal slice is curving toward $N$, negative if it's away.
 
@TedShifrin Oh I didn't know that, I thought the attaching maps had to strictly go into the previous skeleton
 
But the $k$-skeleton includes everything of dimension $\le k$.
Double-check your definitions.
 
Ohh you're right
Okay that clears up everything
 
11:04 PM
Whew.
 
the additive group of a local field is self-dual...
wait what's the dual of $\Bbb C$
 
Thanks again @TedShifrin :p
 
Sure.
 
ah, $\Bbb C$ should be self-dual still, since $\Bbb C=\Bbb R^2$ and $\Bbb R$ is self-dual
$\Bbb C \to \Bbb T : z \mapsto e^{2\pi i \operatorname{Re}(z)}$ is a character?
 
@TedShifrin @LeakyNun howdy
 
11:10 PM
heya @Jake
 
@loch!
 
@TedShifrin currently doing SL equations
rather interesting stuff
 
Ah ... I taught that once, centuries ago.
 
I can feel myself becoming more of a mathematician day by day
harrowing thoughts
 
LOL, @Jake: Should we send you to a psychiatrist?
 
11:13 PM
I see so many people working on start ups and getting really good money with alot less effort tahn doing pure math and sometimes i wonder if i regret spending hours lear ing math. I know i like it and enjoy it its just doesnt feel rewarding except in your head :p
 
If your goal is to be rich, probably there are better avenues.
 
Do you guyz have second thoughts?
 
@ManolisLyviakis every day
 
I loved (and still love) teaching and that was my main motivator. Publishing some really cool papers was a (necessary) plus for me. Most people who go into research math are very driven by research.
 
not about becoming a tech startup guy though.
 
11:15 PM
:\
 
not so worried about that one.
 
I start up my computer every day, if that counts
 
For me the only other plausible career would have been linguistics/teaching language or running a restaurant. That's a hell of a lot harder.
 
@ManolisLyviakis personally I’m a physicist. So im quite driven by learning about the world.
 
11:16 PM
I literarally have a friend that learned python like a year a go and gets paid 1600 doing really easy things haha
 
I don't think any of us would be doing maths if we were motivated by money
 
I don't have a good picture of $\Bbb Q_p$ in my head
 
True that is true im of the same thinking i just thing those things in my bad days when i dont understand math haha
 
I'm driven about not having anything else to do lmao
@LeakyNun the picture of $\Bbb Z_p$ is that you have $p$ circles (representing the reduction mod $\Bbb Z/p$), each with $p$ circles inside, etc; the actual elements of the p-adics correspond to your choice of infinite nesting sequence of circles, but it's useful to not think about that and instead just think of the nesting circles themselves
Then the picture I have of $\Bbb Q_p$ is a zooming out of this process of zooming in: you progressively add $p$ copies of the old bin of circles you had, and then draw a big circle around it
 
interesting
 
11:19 PM
If the Cantor set looks like the number of ways to go down an infinite rooted tree (with "root" at y=0), then this looks like the number of ways to go down an infinite tree where the root is at unspecified nonpositive integer height
 
@Manolis: Here's a little story for you. I took 4 courses from Michael Artin (who's known in this room for his algebra textbook ... as well as his famous name). He commented to me once that he went into algebraic geometry because it was the hardest thing for him (by comparison with analysis, topology, etc.). Mathematicians seek challenges. That's what makes them thrive.
 
k, so if linear transformation $F$ has only eigenvalue $\lambda = 0$ and if $F(V) = \lambda V$ and $W$ is any lineary independent vector with $V$ and $F(W)=0$, thus i can conclude that $m(F) = 0$ because if we take a vector it can be either lineary dependent or independent with $V$, if its independent then $F(U)=0$ by assumption, otherwise $U = \alpha V$ thus $F(\alpha V) = \alpha F(V) = \alpha \lambda V = 0$ and so $m(F) = 0$, am i right?
 
I know martin hahaha awesome story
 
No, @chandx.
 
daym, why is that @TedShifrin
 
11:21 PM
Oof, prom is in May. I'll let people know I'm not going because I have to do math that night.
 
Why must every vector be an eigenvector?
 
well i assumed that only V is eigenvector for lambda
 
So what if you have another vector $U$ that is not a scalar multiple of $V$?
 
then from my assumption it's 0
i mean F(U)=0
 
Your assumption? Who told you that was a valid assumption?
 
11:24 PM
haha, well im just askin if conclusion is okay according to assumptions
doesnt matter what assumptions are
 
So it doesn't matter if your answer to your question is wrong?
 
well im just asking is valid conclusion that $m(F)=0$ if following conditions are satisfied:
-$F$ is linear transformation in $\mathbb{R}^2$
-$F$ has only one eigenvalue $\lambda = 0$
-if $W$ is lineary independent with eigenvector $V$, then $F(W)=0$
is it valid*
 
That makes $W$ an eigenvector as well.
So you're saying you're assuming you have a basis consisting of eigenvectors? That was not the original question.
 
well maybe i asked wrong way at first
 
Is this a question in your homework/textbook? If so, I want to see it PRECISELY.
 
11:30 PM
haha, well, im just doin proof of some theorem
 
Haha, I think what you're doing is probably wrong.
 
daym
 
Just an educated guess based on teaching linear algebra for 40 years.
 
im provin this little stuff:
Let $\lambda$ be double zero of $\chi_A$, where $A \neq \lambda \mathbb{I}$, i. e. $\chi_A (x) = (x - \lambda)^2$. Then there exists two lineary independent vectors $U$ and $W$, such that $AU = \lambda U$ and $AW = U + \lambda W$
 
That is a very different statement. Even a correct one.
 
11:36 PM
do we need more assumptions?
I feel like $A$ needs to be 2x2
 
That looks fine to me, Leaky. We're in dimension 2.
 
so i divided it to two cases, $\lambda \neq 0$ and $\lambda = 0$
ye, 2x2
 
He said that to start with.
 
ok then
 
You can easily reduce to the case $\lambda=0$. But the stuff you were saying was nonsense.
 
11:38 PM
yet another example of being able to see through the question clearly once you learn some higher theory
 
Note that the assumption, with $\lambda=0$, is precisely that $A\ne 0$.
So you have to use that assumption that $A$ is NOT the zero map.
And yet the characteristic polynomial is $x^2$.
@Leaky: One doesn't need higher theory for this.
 
@TedShifrin of course, but once you know the higher theory you'll be clear what's really going on
 
But saying stuff like that isn't pedagogically helpful.
As is often the case with you.
 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
Oh, @ÍgjøgnumMeg, how'd your interview go?
 
11:42 PM
lol hi @Ted, I'm just lurking as usual
I think it went well, I struggled with some of the exercises I had to do
 
@TedShifrin and pedagogically I've always believed that learning higher theory can actually help you with the current syllabus
 
They were more interested to see how you struggled, I'm sure.
@Leaky: That will not make you a good teacher.
 
and pedagogically I've already said that "you'll be clearer as to what's going on", how is that not pedagogical
 
How to integrate $\frac{\sqrt{z^2+ a^2}}{\sqrt{z^2+2a^2}}$ wrt to z ?
 
Yuck @Nobody.
What if you put everything under one $\sqrt{}$ and simplify the algebra?
 
11:44 PM
@Ted I bet, I was also interested in how hard it was. The questions were just like "Example: Divide 363 by 3", now design a question that is at the same difficulty level. The idea was (at least obviously in this case) that all the digits are divisible by $3$ so there's no carrying if you use the "bus stop method" (this is supposed to be for school kids)
 
They were interested in your elementary math instincts (and most math majors haven't thought about such things AT ALL) and pedagogical skills.
 
of course, the examples got harder as you went on (what techniques are employed by the question and can you engineer a question using numbers that use only the techniques employed by the example)
 
Did you know that there are two ways to think about division problems $m/n$?
Actually, if you take the job, I'll recommend a textbook for you to get. Very insightful.
 
@Ted right, and I found it quite a struggle, which was both nice but daunting lol
 
Yeah, math majors are like Leaky — off in the sky, with no idea about how kids think or should be taught.
Rational numbers are equivalence classes. Yeah, right.
 
11:46 PM
@TedShifrin ok. What After that although i don't know how to write that in mathjax.
 
well I've had some experience teaching, but teaching undergrads is very different to teaching school kids
 
@TedShifrin I don't plan to teach kids
 
@ÍgjøgnumMeg: I've taught courses for future elementary teachers. A former colleague wrote a fantastic book.
Thank God, @Leaky.
 
well ye, i see that then $A \neq 0$ but i don't see how to reduce two cases to only one $\lambda = 0$
 
You are obnoxious enough with college students.
What is under the square root, @Nobody?
@chandx: That is the easy part. Look at $A-\lambda\mathbb I$.
 
11:47 PM
@Ted that's cool, I actually don't plan on teaching primary or secondary education, but the ideas/experience I'll get (if I get it!) are useful nonetheless
 
no, no, @ÍgjøgnumMeg, but the job may involve some stuff from lower levels, not just calculus and trigonometry.
 
@Ted yeah it definitely will; the position I'm going for is actually for GCSE standard (upper secondary school) so it's mostly teaching basic stuff, I think factorising and solving quadratics is on the more difficult side
 
"If F is nonarchimedean, however, one cannot take the derivative of a function F → $\Bbb C$"... I beg to differ?
 
@TedShifrin ok . $\int \sqrt{1-\frac{a^2}{2a^2+z^2}}dz$
 
(nonarchimedean [local field])
@TedShifrin would you recommend [me] doing Tate's thesis for my 3rd/4th year project?
 
11:51 PM
I have no idea.
 
@TedShifrin were you saying this ?
 
@Nobody: So that suggests that you try to make $\dfrac{a^2}{2a^2+z^2} = \cos^2\theta$, for example.
Dunno how it turns out.
Or were we supposed to be doing some sort of contour integration with $z$ complex?
It looks pretty hopeless to me.
 
@TedShifrin ok let me elaborate. I may have been giving uncessary riguor. Without clearly specifying the problem. I was doing a double integral $\int \int \frac{dxdz}{x^2+a^2+z^2}^(3/2)$ where both limits go to 0 to a. After doing the first integral i got that.
 
You want to switch to polar coordinates. Even though the region is a square. Do half the square in polar coordinates.
I wish people would give the original question here ... :P
 
@TedShifrin the lower part is to the power 3/2 .
 
11:56 PM
I don't care :P
You need ^{3/2}
 
@LeakyNun Ask Kevin.
 
@MikeMiller well he said it's great
 
@TedShifrin i know its pathetic to answer simple question complexised by authors . :p
 
Yeah, polar coordinates is your friend.
 
@TedShifrin then how to do that ?
 
11:59 PM
@TedShifrinhow would I say something can’t be less than in formal notation?
 
@TedShifrin lmao u owned him
 
like how you can say a variable cannot =0 with the slash through the equality sign
 
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