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1:00 AM
We had the snake Lemma on our midterm @MatheinBoulomenos. That was not fun lol
 
Presumably you only had to prove exactness at one point, Antonios. Otherwise, it takes the whole hour.
 
@TedShifrin Especially at Berkeley these last few years. A lot of my female friends told me some horror-tales. A lot of the male grad students abused their positions.
 
It happens with faculty, too, Antonios.
 
@TedShifrin believe it or not, he wanted us to do the whole thing. We did have 2 hours. The average ended up being like a 40 lol.
 
And a certain about of homophobia, too.
 
1:01 AM
I don't disagree with that, though. I think certain stuff is easier to do yourself than to see a proof and understand it
 
@Mathei: I typically did one argument and left the rest to the reader = students.
 
@MatheinBoulomenos Definitely. It's still a bit of a dumb exam question (in my biased opinion)
 
I think you have to demonstrate one diagram chase.
Totally dumb, Antonios.
 
The homophobia and misogyny seems to be getting an increasingly troubling issue in the US
 
yeah, one diagram chase should be demonstrated
 
1:02 AM
with all the alt-right and white supremacy...
 
I also think that snake lemma is a dumb exam question
 
Balarka, well it's a permanent mess in Russia and other such countries.
I dunno about India.
 
The issue with Sug-woo was/is that he is a super-genius and totally misunderstood how difficult his homework/exams were.
 
@Mathein I doubt we're doing that. Our Prof said we're doing the basics of rings/ideals, a bit on PID/factorization in polynomial rings, Noetherian rings, general modules, and then modules over a PID
 
India is pretty fucked. I'm not even counting it.
 
1:03 AM
sup chat
 
Finally, Eric shows up.
Eric, I need your PDE help to finish answering an MSE question.
It's actually an interesting question.
 
much busy lately
what is the question
 
@Daminark that's the stuff we did in linear algebra. It's really important. Most texts on e.g. commutative algebra will assume that you know that
 
This is the question.
 
I'm trying to answer a question about whether an overdetermined system of first order PDE has a (local) solution.
 
(It's the original Morin's eversion)
 
Given a skew-hermitian matrix $\Phi = (\phi_i^j)$ of $(0,1)$ forms (satisfying an integrability condition), I want smooth functions $f_i^j$ so that $$\bar\partial f_i^j + \sum f_i^k\phi_k^j = 0.$$
 
hmm
 
our linear algebra final had some exercises from Atiyah-Macdonald if I remember correctly. They had to adapt the grading scheme dramatically
 
1:06 AM
That's rough
 
(in addition to stuff like computing Jordan bases which takes forever)
 
I think I actually write relatively fair exams, but in upper-level courses I was happy with an 80% for an A, scaling appropriately downward.
 
Some people got the best mark (not sure if that corresponds to A or A+ or whatever) with little over 50%
 
@TedShifrin The only thing that ever grinds my gears with exams where ~70 is an A (or something like that) is when scores are posted without any explanation of what they mean.
 
@EricSilva: Part of the issue is whether (and I believe the answer is yes) there's an analog of Frobenius for $\bar\partial$. It should just follow from $\bar\partial^2 = 0$ analogous to $d^2=0$.
 
1:07 AM
@Antonios-AlexandrosRobotis last quarter my class had 67% as an A
 
@Antonios: I always showed my students the grade distribution and how it broke down.
 
i would think so
 
yeah @Daminark I've been there before.
 
@EricSilva: Odd that I can't find this in print anywhere. :(
 
Though our Prof was kinda nice
Like, 60-67 was an A-, and I think 10/25~ people got at least that
 
1:08 AM
hmmm
 
they originally planned 50% as the cut-off for passing the class, but they ended up giving the best marks for that
that's how much worse our class was than they expected
 
I seem to have stumped Rafe with the question, Eric. I emailed him, but he was on his way to Spain for a conference.
 
@Daminark A professor at Berkeley was infamous for failing people (Alexander Givental). His 104 (1st sem analysis à la Baby Rudin) had an average grade of a D most semesters. By contrast, other professors had an average of B- usually.
 
Well, a good department shouldn't allow things to be so grossly out of whack.
 
Welcome to UC Berkeley LOL, where anything was possible.
 
1:10 AM
But I was notorious for teaching tougher classes than most of my colleagues. My grades weren't so far out of line, except for a few ridiculous faculty.
 
(not taking away from the professors/students themselves)
I'm all for super challenging classes, but students should not be penalized for taking that sort of risk.
 
Morale is an issue.
 
What do you mean by morale?
 
But some grad students didn't take classes from me because they wanted an easy A. And I didn't believe in that.
I mean getting an F in one section where you would have had a B in all the other sections is not fair.
 
1:12 AM
@TedShifrin that's a stupid attitude
 
He might argue the other people's standards were too lax. There needs to be some departmental agreement on grading, but ...
 
I will give it more serious thought when I finish my reading for tonight @Ted but i totally believe there's a Frobenius for $\bar \partial$ at least
 
@Mathei: In first-year courses I gave real grades. In more advanced courses, most faculty gave automatic A's. I conceded that I'd give an automatic B if you attended all the classes, but you had to do some work to earn an A.
@EricSilva: I'd love to talk with you about this when you have some time. :)
 
I took some honors courses, and found them to be consistently more enjoyable experiences than the basic courses.
 
why study math in the first place if you want to have it easy? Surely there are less demanding things than math
 
1:13 AM
yeah seems interesting
 
@Mathei: I was complaining about grad students there, not undergrads ...
In the US we are way easier on undergrads than in Europe.
 
dumb question, what is an honors course?
 
nfi
and im in an honours program
 
@Ted iirc nirenberg might have proved a complex frobenius but i do not know its statement
 
Covers more, gives more homework
 
1:14 AM
Harder classes with more demanding content, @Mathei, typically.
Some places honors is a joke.
 
Read as "more interesting content"*
 
some places they're completely absurd
 
At UGA you had to be in the Honors program, rather than being prepared for an honors course in a certain field.
 
That sounds nice! I wish we had honors algebra here, although at least the second part of our algebra sequence was already pretty interesting
 
For instance an honors calc course might have proofs whereas a regular might just consist of integrating.
 
1:15 AM
So the courses tended to be just the equivalent of regular core courses, but taught for students in the program. The math classes I created were outliers ...
 
for us the only difference is a supervised research project and minium gpa of 6.5 to not get kicked out well and more required math classes
 
Youtube directed me from that sphere eversion video to this
 
on what scale?
 
1:16 AM
out of 9
 
Whoa.
 
its like between and B+ and and a A-
 
that is the weirdest scale
 
isn't gpa measured on a scale of 4 usually
 
yeah C=2, B=3, A=4 or something
 
1:17 AM
not in canada
but yes
 
@MatheinBoulomenos classes in America are for the most part easier than in Europe is the vibe I get, even your standard classes are probably at least as good as our honors
 
Here everyone takes the same classes. Having honors classes sounds like a good system
 
gpa 4= gpa of 8 on our scale
 
@Daminark ah that may be true
 
1:18 AM
main diffrence is each grade gets a number
that is an integer
 
yeah we specialize later i think
in the US
 
@Faust I see
 
A+=9 A=8 A-=7 etc
but its pretty hard to get an A+ for the most part
 
but then we don't really have "grad" versions of the basics. We don't have "grad algebra", because we think of general abstract algebra as undergrad material. That means our undergrad algebra sequence has to prepare the people for algebraic number theory and algebraic geometry, for example
 
at least imo
 
1:20 AM
@MatheinBoulomenos how long is grad school there
 
Actual grad schools are really rare in Germany. We always do a masters first and I think that corresponds to the first part of grad school. If you're accepted as PhD candidate, you start working with a group of researchers from the beginning
 
Demonark: Chicago's Honors is way different from most school except maybe Harvard's 55. :)
 
@TedShifrin archive.org/details/complexfrobenius00nire i haven't looked at this but maybe it says something
 
I've heard harvard's 55 is brutal
 
@TedShifrin just honors analysis of course, honors algebra isnt the same kind of monster
 
1:22 AM
Yeah honors algebra is a bit sad by comparison
 
@EricSilva that is the oddest statement
 
I'm always equating "grad course" = "masters course here in Germany" in my head
 
It's really honors analysis, and really really it's Soug
 
lmao
 
i thought soug's quarter was the easiest of the three
i thought marianna was the hardest
 
1:23 AM
@EricSilva: That's the Newlander-Nirenberg theorem for integrability of complex structures, I bet. ...
 
Marianna gave the hardest problems but gave 5/week
 
ya we had more my year though
it seems like she was harder on us than you guys
 
I'm gonna head out, and focus properly.
Good night all.
 
gnight
 
Bye Antonios :) Keep warm.
 
1:25 AM
Bye @Antonios
 
fat chance. @TedShifrin
 
See ya
 
Yeah she was. But Soug's class wasa nightmare
 
Im really having trouble getting back into the semester :( really wanna play video games
 
Bad Faust.
 
1:26 AM
I have to decide
what I want to read
 
@TedShifrin yeah i dont really know the complex story
 
You could be illiterate like our president.
 
i should learn more
 
Once upon a time, I did stuff like playing video games, going outside although I don't have class etc. Then I started doing math
 
@MatheinBoulomenos yeah i really wish i could get my math load down to only 65hrs a week
 
1:27 AM
So Newlander-Nirenberg is integrability of almost-complex structures, without assuming real analyticity. @EricSilva. I'll look more at what you linked me.
 
its just not possible for me not smart enough
 
ah i see
 
@TedShifrin At least he's humble about it
 
lmao
 
yes, he's very stable genius.
 
1:28 AM
i think hes got some dementia going on
 
indeed ...
 
as an impartial (how the hell did you guys elect that idiot!?) observer
 
He's the biggest troll of all time
Literally trolled his way into the White House
 
there's still a great likelihood that Putin sabotaged the election, Faust. Who knows.
 
i never thought i would miss the day when Bush was the president of the us, at least he wasnt a total **** even if he wasnt the brightest
 
1:31 AM
@Faust demagoguery basically
 
hmm thats my new word for the day...
 
@TedShifrin interesting
well that kgb man can do anything
 
@TedShifrin i certainly hope so the alternative is not good...
 
Well, we shouldn't be doing politics here ... but there are a lot of white supermacist American (and European, too) citizens who voted for Trump only because of prejudice.
 
its just mind blowing to go from a black president to a white supremacist like wth
i digress i got lots of math lectures to watch
 
1:34 AM
The alt-right politics in the US is really bad, from what I infer
 
that stable stuff is hard. Maybe if I was a stable genius, I'd understand some stable homotopy theory
 
it's truly an issue most places in Europe, too, Balarka
 
@TedShifrin prejudice is a way stronger motivator for voters than things like actual policy
 
right, Mathei ... work on that ... semi-stability doesn't suffice.
Yup, indeed, Eric.
 
@TedShifrin Makes sense
It's just that so many right-wingers in the US brag about the "American values" and how they are superior to the rest of the world's culture and morals.
It's kind of silly
 
1:37 AM
Oh, the irony is deadly.
 
the right people in Germany are mostly anti-refugees
 
@TedShifrin i am litterally taking all of the courses listed in your playlist this semester plus some number theory wish i finished them this summer :(
 
And the public face of these dudes are people like Ben Shapiro and Milo Yiannopolous
 
this is a thing for the mainstream right in america and not just the alt right really @Balarka
 
Who are so impossibly wrong headed and come up with made up logic to promote propaganda
@Eric I suspect so
 
1:39 AM
what do you mean, @Faust? My playlist?
 
yeah the one thats like 112 hours i need to know everything in all of them ++ to cover three of my classes this semester
 
ohhh ...
 
Funny thing: the sub-countries (don't know the official English term, they're like states in America) in which there were the most demonstrations of "patriotic Europeans against the islamization of the occident" were also the sub-countries were the fewest muslims in Germany live and where there are the fewest refugees
I guess "federal state" is the official term
or province? I don't know
 
I'm trying to think of the term, Mathei.
 
id really like to visit german for a few weeks
drink alot of beer
think about funny math
come home.
 
1:43 AM
@TedShifrin just want to make sure I understand some notion of sheaves.
So here each of the $A(X)$ etc is just a group right and we are looking for to construct the group element c from those $b_i$ i.e glue them in some fashion
 
Just looked up the actuary exam and jeez
 
@Daminark on what ?
 
The subtlety, Karim, is that surjectivity of a sheaf map does NOT mean surjectivity on sections.
You just know it on small sets.
 
I see
Yeah sheaves just capture local data.
 
@Adeek probability and financial math appear for sure
Not sure exactly what else
 
1:47 AM
@Daminark did you hear about the bootcamp
 
do you want to know something funny @Daminark speaking about financial math
So in my last year of undergrad I had economics right. I never attended a class because it was super boring. Then, I studied 2 days before the final and ended up getting 90 class avg was like 65
lol
 
@EricSilva got an email from Jared, though we don't know much
 
yeah if i dont get into REUs hopefully that happens
Schlag's already submitted my letters so my apps are basically almost done
 
Oh yeah I gotta do that at some point
 
I assume you're not applying to the CA one, Eric. I could almost guarantee you'd get that if you wanted it.
 
1:51 AM
nah i think if i had to choose between that one and staying in chicago another summer id choose to stay in chicago
 
I figured. Oh, by the way, I was wrong. Nirenberg starts out referring to Newlander-Nirenberg.
 
I want to do REUs, too. That sounds really cool. We don't have something like that
 
interesting
 
You're too advanced for them, Mathei.
 
oh okay
 
1:54 AM
alright well... thanks for all the fish im out
 
@Faust So long, and thanks for the Douglas Adams reference!
 
@Faust peace
 
I don't know what to do
More h Principles? More geometry? Learn measure theory? Dynamics?
Maybe I'll just listen to vaporwave
 
You could prove the real Gauss Bonnet :P
 
I plan to do that. I need to familiarize myself with the curvature 2-form first
And the form-al setting of diffgeo
in general
 
2:00 AM
True enough ... good thing I sent all the notes.
 
Yep :)
 
It's an $\mathfrak{so}(n)$-valued $2$-form, of course.
 
@BalarkaSen finite group theory
 
no one cares about finite group theory.
8
 
Daminark gets roasted everytime
 
2:03 AM
people care about $S_{n}$
 
who could blame me?
 
they're weirdos but they're out there
 
@TedShifrin well that's just false though
 
I blame @Ted
 
If you say only degenerates do I'd prob just not talk
 
2:03 AM
What am I blaming ted for?
 
sure, PVAL, pile on. Happy new year, anyhow.
 
Hey @PVAL
Let's all star that message just to roast Daminark
 
no one cares about finite group theory. -Ted Shifrin 2019
 
oh, time for Ted to disappear for a few years.
 
@BalarkaSen originally I was having second doubts about doing math but after these roasts I'm dedicating my life to proving a point wrt roasts. Not sure which point, but a point.
 
2:06 AM
ive got to go read a book
bye chat
 
bye Eric
 
@Daminark Good. I'd love to see you doing mathematics.
 
See you Eric!
Wait crap that didn't work the way I wanted. I played myself AMA
 
does anyone seriously blame me for roasting Demonark whenever possible?
 
@TedShifrin It's an inside meme, really
@Daminark lolol
 
2:09 AM
A roast sounds tasty.
 
you're not vegetarian?
 
whew.
 
you could be a vegan and still love roasts
roasted broccoli
tastes 10/10
 
@TedShifrin nah if anything the roasts are my motivation for being the way I am. I'd actually learn calculus if not for... Okay I can't say that with a straight face but you get the idea
 
2:10 AM
most vegetables are great roasted ... brussels sprouts, carrots, parsnips ...
I get it, Demonark. I didn't just fall off the turnip (or broccoli) truck.
 
finite groups are great. Sometimes when people talk about Lie groups I say "I'm very interested in Lie groups, especially zero-dimensional compact ones"
 
How do we get $\limsup \max (a_n, b_n) \leq \max(\limsup a_n, \limsup b_n)$ here?
 
@Mathei Do you want to complete my proof-sketch here?
I am not really thinking about it but I'd like to see a proof
 
I'd like to, but I don't really know things about tilings
 
I think all you need is to figure out the symmetry group of such a possible tiling
That should be a computation ...
(And then prove it doesn't embed in SL2(R))
 
2:25 AM
it looks pretty dihedral to me
 
Oh, indeed?
 
@BalarkaSen roasted brocolli is great
 
it has at least $D_4$ as a subgroup.
I won't spell out the whole representation theory of $D_4$ here, but it's not difficult to see that there's only one faithful 2-dimensional representation
 
Balarka isn't faithful, though.
 
but this representation does have matrices of determinant $-1$
this should do it
(all these representations are defined a priori over $\Bbb C$ but can actually by given over any field (not of characteristic $2$)
 
2:32 AM
Okay, I want to understand this in step by step. By $D_4$ you mean symmetry group of the square, just to clarify notation? I agree then; the symmetries of the fundamental square (hyperbolic rotation/reflection) should be symmetries of the whole lattice.
 
the color of the fish are not relevant, right? only the red lines
 
Yes.
 
yeah, symmetry of a square
 
Okay great
And next you claim there's only one $D_4$ subgroup of $SL_2(\Bbb R)$ or what? Upto conjugacy?
 
there's no $D_4$ subgroup in $SL_2(\Bbb R)$ at all
 
2:34 AM
Ah ok great
How do you see this?
 
there's only one $D_4$ subgroup in $GL_2(\Bbb R)$ up to conjugace and it isn't contained in $SL_2(\Bbb R)$
okay, we need some basics from representation theory
 
I don't believe you. What if I take a unit hyperbolic square in $\Bbb H^2$ with center at the origin of the disk and look at the rotational and reflectional symmetries of it?
(I mean I do, I am just trying to sound aggressive :P)
 
are these symmetries realized by isometries of $\Bbb H^2$?
 
Is it not? Hm.
Rotations work fine
 
Sure.
 
2:36 AM
I don't think you can get reflections, though
 
Sure you can.
 
I mean reflect across the diameter of the disk...
 
okay then I have no idea
 
That's a hyperbolic isometry
 
I'm not paying attention to the thrust of this conversation, but ...
 
2:38 AM
Oh, SL_2(R) is the oriented isometry group of H^2
Orientation preserving dudes
 
this makes more sense
 
Right, no reflections in $SL$.
 
@MatheinBoulomenos Still a cool fact that $D_4$ does not embed in $SL_2(\Bbb R)$. (I'll learn the proof of this from your at some point).
But I guess you're not really using anything special about the tessellation other than the center square
 
it's really just some basics of representation theory. You can classify all homomorphisms $D_4 \to \operatorname{GL}_2(\Bbb R)$ up to conjugacy and then you see that some are not injective and the others are not contained in $\operatorname{SL}_2(\Bbb R)$
 
The proof should involve a careful analysis of how the isometries of the squares and the triangles interact.
@MatheinBoulomenos I see.
 
2:43 AM
Hey @ted, quick question: Gotta run in a second, but I was wondering...is there an old website at Georgie or elsewhere that would have supplemental materials to your video lectures? I.e. Homework assignments, etc... from the textbook?
 
No, @Cookie. But if you email me, I can email you all that stuff.
 
:D I'll email you then! The address in your bio right?
 
yup
 
Cool. Thank you Ted!
 
You're welcome.
 
2:45 AM
just got some geometric approach and it's selling like a god church (email in bio)
I'm sorry I had to do that
 
Hello! $C^n$, where $n\in\mathbb N$, is the set of continuous, $n$-times differentiable functions. However, while reading a publication, I saw $C^\beta$, where $\beta\in\left[1,2\right)$. What in the world does this mean?
 
smacks Balarka twice
Look up Hölder, @Raptor.
 
Are smacks gonna go the way of eye rolling?
 
Excellent suggestion
 
non-integral smacks must be in the future.
Think how dull this chatroom would be without my ... spice.
 
2:48 AM
Truly. We have to endure Daminark's puns instead
 
Well, maybe that's due penance.
 
@TedShifrin (on the Group Theory quote) Ouch
 
It was slightly in exaggeration.
But only slightly.
OK, I'm outta here. Time for dinner.
 
I wouldn't know, but as an outsider... I remember one student's poster on lattice diagrams of $D_{\text{something}}$... and just thinking, what's the point?
Bye @Ted
Hmm...
19
Q: Is finite group theory still a fruitful area of research?

Noomi HollowayA while back I was learning about finite groups in an algebra class. I mentioned to a friend that finite group theory might be an interesting area of research to pursue. She asked something along the lines of "Isn't finite group theory 'done?' I thought that ended with the classification theorems...

 
Bye @Ted
One might as well ask "Isn't 3-manifold theory 'done'"?
 
2:59 AM
A large chunk of it is
But there's still a lot of 4-1 theory out there
 

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