7:00 PM
Very cool, @Tobias. If we ever end up in the same corner of the earth, we can play :)

Yeah, I think they are looking into making the automatic mahjong tables do the same, but those are too expensive for most local clubs to afford

@TedShifrin i cant think of such a function, example?

@Silent: Do you have any thoughts?

And affording enough for an actual tournament would probably require the game to be more popular outside of China and Japan than it currently is

does anyone play seep? (card game)

7:01 PM
Have you ever played the game Carcassonne, @Tobias? It's quite cool, somewhat mathematical. There's even an iPad app for it.
(I also happen to love the town in France after which it's named.)

@TedShifrin I have played it a few times. I like it as a game to play with people who don't regularly play board games, since it is fairly simple and not too deep strategically (so people don't end up spending too much time trying to optimize their play)
I have considered getting it myself, since it is also of an appropriate level of difficulty to play with my daughter without having to alter the rules to make them easier

I find it sufficiently challenging myself :)
DogAteMy!!

Ted!!!

sup chat

heya ERic

7:06 PM
how's it going

Eric, if you're interested, there's someone asking a bunch of minimal surfaces questions (based on Minicozzi/Colding's book) on main.

what's going on

heya Antonios
Anyone left in the algebra course?

seems she did end up curving the exam, or at least so I've been told.

Still it would be nice if people learned something ...

7:09 PM
yeah, exactly.

Hmmmm

That reminds me. Got the preliminary plan for re-exams today. 6 people eligible for the algebra re-exam. Should not be too tough to grade those, though it feels like a shame to have to make an entire exam set just for 6 people

@LeakyNun ?

I’m trying to put together what I thought I figured out, but now I don’t trust it. Bummer

@Tobias: I've written several qualifying exams just for one student over the years.

7:10 PM
@LeakyNun How does origami make the fact that the torus quotiented by a meridian and parallel is a sphere obvious?

@Semiclassic: Have you found an error in the write-up?

@TedShifrin How long are those?

3 hour written exams, Tobias.

An error in my use of a certain bound

Oh, you mean like viewing the torus as a square with opposite sides identified? @LeakyNun

7:10 PM
ok, so about the same (this is a 4 hour exam)

The premise was stronger than I realized.

Aha.

@TedShifrin ill check it out

@AkivaWeinberger right, and then the quotient basically identifies the boundary of the square

Don't make premises you can't keep

7:11 PM
so you get a sphere

Right, I see

DogAteMy: With talk like that, Demonark will materialize.

The context was that I wanted to find a bound on $\text{tr}(U^\top U S)$ in terms of the Frobenius norm of U and the eigenvalues of S
But the argument I saw assumed S was positive definite, and mine isn’t

Can you make a perturbative argument?

Dunno.
The awkward thing is that I have an example for S, but I’m not sure how I should be generalizing it
The example has S being symmetric and orthogonal.

7:15 PM
@TedShifrin These programs do feel a bit slow at times, since I already know the rules and a bit about bidding. But on the other hand, they do teach some fundamentals I did not know. Just went through a chapter on finessing, which is not something I had really considered before.

Yeah, and if you have a choice of finessing either way, do you have information from which to infer which way is more likely? (Bidding/counting points that have shown up in the respective hands, signals, etc.)

@TedShifrin This is before anything about bidding. But it did make a point of having you play as many cards as you could safely do before choosing which finess to take.

Yup, lots to learn.

in that example I can do a Cauchy-Schwarz argument (since that trace can be understood as the Frobenius inner product) in order to deduce a bound

indeed

7:17 PM
So I like that.
The weird thing, which I feel like I should understand, is that the bound should only be saturated when $U=US$
Where U is 3-by-4 and S is 4-by-4 in my example
Obviously, the rank of U is at most 3. But i feel like I should be able to say more than that.

@TedShifrin yup
we got the second pset today

Excitement.

It's $\sum_{i,j}\langle u_i,u_j\rangle s_{ji}$, which is a kind of dot product if you interpret them as vectors with $n^2$ entries.

mr @anon!

Right.
You can view it as the Frobenius inner product of U and US with S orthogonal
Or, well
In the case I understand, S is orthogonal
I’m not sure I really need that but for now I don’t know how to dispense with it

7:25 PM
Is anyone here familiar with intersection homology?

I am new to Math.SE. I have seen an accepted answer to some question that contains a fundamental mistake. Can you tell me what to do? If this is not the right location to ask this question, please excuse me and tell me ahere to look.

guys , how is $\dfrac{f(1+x)-f(1)}{x}=f^{'}(1)$ limit x $\to$ 0

@Helmut: All you can do is put a comment explaining why it's wrong.
@Tanuj: It is NOT, unless you put limit in there.
oh, there is a limit now.
That's the definition of the derivative.

ok thanks

@Ted Shifrin OK. I already did that - and wrote a better answer... Thanks

7:31 PM
Cool :)

@TedShifrin
How was this bit done ? Where did the 6 from the upper and lower limits disappear ?

Hello

@Tanuj: I assume the function is periodic with period $T$ or something.
Hi Demonark

@TedShifrin yes.

Period T? Or period 6?

7:40 PM
Is there any property for periodic function's integration ?
period T

Not 6.
@Tanuj: If you integrate over a period (or several periods), it doesn't matter where you start.

Hi @Dami

Oh I was thinking period 6 because you translated by 6, that makes sense

Draw pictures.

Hey @Alessandro, how's it going?

7:41 PM
@TedShifrin okay , so how would you state this property mathematically ?

@Daminark pretty well, what about you?

$\int_a^{a+T} f(t)\,dt = \int_b^{b+T} f(t)\,dt$.

Same here, basically recovered from the flu modulo a stubborn cough

@TedShifrin thanks :)

I doubt the stubborn cough generates a normal subgroup

7:42 PM
leaves Balarka and Demonark to descend into humorless hell

Tired

hi Mike

@TedShifrin I could replace $b=0$ , right ?

Hey Mike

@Balarka

7:43 PM
It's true for any $a$ and $b$, @Tanuj. Can you prove it?

Are you familiar with intersection homology?

We go into the humorless hell and make it humorous. But yeah it probably doesn't but you just take the normal closure anyway so it's fine
Hey @Mike!

@TedShifrin idk , but thanks.I'll give it a try.

I tried asking yesterday but I guess you didn't see, have you ever taken that model theory course? @Dami

@gian Unfortunately no

7:43 PM
Bye for now ...

Okay, I will post then. Thanks anyways :)

Nope, I will hopefully take it next year

@TedShifrin Bye ! Take care :)

See you @Ted!

Ah, that's a pity, I had a model theory question

7:48 PM
Who in the name of jibberjabber flubberflickering hell is littering the star panel with trash
Some kind soul unbanned me
But I rage in thy general direction whoever flagged me

@BalarkaSen Maybe consistently don't use profanity.
(I unbanned you because your message was not actually offensive, but don't count on that happening every time)

I do think that it's reasonable to consistently use profanity, but I also think it's fair to assume a consistent ban from it