Mathematics

ixtmixilix

12:07 AM

@mixedmath i bashed my skull in and i can still laugh.

Henning Makholm

12:18 AM

It's late; I'm off. Goodnight to whomever is out there.

mixedmath

12:52 AM

Goodnight Henning

oh - I'm way late

ixtmixilix

c98... c97...

c7... your system had a kernel failure... c96... c87...

stream of consciousness innit

c14... d78...

hurray, i just finished finding and replacing the regex i could not be bothered to figure out how to write

whoever's listening, i have this question> has studying a particular branch of mathematics ever made your dreams more vivid?

mixedmath

1:10 AM

I used to get algebra nightmares every now and then

but I don't think that's quite what you meant

ixtmixilix

not really, but sorta. i guess that's the opposite of the sort of dream i'm talking about

this is a 'WOW' sorta dream

could be intricate visual detail

could be you on a stage directing an entire orchestra for 8 hours with music that just comes out of your head

i guess (a la das Parfum) also some very complex smells

J. M.

2:04 AM

@anon Henning did it for one of those deleted questions he asked about.

ziggurism

3:29 AM

Hi. I guess stack exchange locks threads for comments after they become old, is that so?

Is it possible to unlock them?

Rajesh D

i've haven't heard about any such thing

ziggurism

Well uh

here is a question from the top of the pile:
http://math.stackexchange.com/questions/86935/homotopy-of-singular-n-simplices

Notice that each "answer" (there is only one) has a link for "add comment"

here is a question from 6 weeks ago or so:
http://math.stackexchange.com/questions/70938/coordinate-free-definition-for-the-riemannian-volume-form

the "add comment" link is not there. It seems that I can still answer the question, but if I want to engage in discussion via comments, I cannot.

or am I missing something? Is it still open for comments and I'm just not seeing it?

are you able to comment on that old thread?

Rajesh D

@ziggu : I am able to find add comment button in both of the questions you have mentioned !

ziggurism

3:45 AM

really?

that's weird.

hmmm

you know what.

for some reason I'm not logged in on that window

I reload in a new window and everything works

mystery solved!

thank you, Rajesh!

Rajesh D

ok

i happened to me sometimes

robjohn

@ziggurism Do you see an "add/show 1 more comment" link?

below the comments.

ziggurism

@robjohn: I do, yes. Actually I see the "comment" link too now. Problem was that I wasn't logged in (in another tab)

robjohn

Ah, okay.

ziggurism

but thank you, sir!

Rajesh D

3:54 AM

hi @rob

howz the day goin

Jacob Schlather

Rajesh

you could look at jump discontinuities with respect to a directional derivative

but I don't think it really makes sense to extend the concept

Rajesh D

4:26 AM

Becaue you can create a function which jumps different amounts and in different directions in each of the straight lines approaching your point. I don't think the idea is as simple. – Alex Youcis

@Jacob : in this case (different amount of jumps in different directions)...for the function to be continuous in some neighborhood (except at that point) of the given point, do we need any restrictions on the amounts of jumps in different directions ?

except at that point

Jacob Schlather

4:40 AM

So you'd say a function has a jump discontinuity

if it has a jump discontinuity

at each directional derivative?

Akram Hassan

7:29 AM

hello there

Matt

7:49 AM

Good morning.

Rajesh D

7:59 AM

good afternoon Matt

Daniil

Hi guys.

Rajesh D

hi

Akram Hassan

8:46 AM

hello there

Matt

Hi

Akram Hassan

hi matt

what are you interests ?

Matt

Mathematically or in general?

Akram Hassan

math first !

Matt

I like topology, algebraic topology, functional analysis and algebra. So far : ) You?

Asaf Karagila

8:55 AM

Do you like Sober spaces?

Akram Hassan

i love geometry but i am an absolute beginner

Matt

@AsafKaragila Did you mean Sobolev spaces?

Asaf Karagila

No. I meant Sober spaces.

Sober space

In mathematics, a sober space is a topological space such that every irreducible closed subset of X is the closure of exactly one point of X: that is, has a unique generic point. Properties and examples Any Hausdorff (T2) space is sober (the only irreducible subsets being points), and all sober spaces are Kolmogorov (T0). Sobriety is not comparable to the T1 condition. Moreover T2 is stronger than T1 and sober, i.e., while every T2 space is at once T1 and sober, there exist spaces that are simultaneously T1 and sober, but not T2. One such example is the following: let X be the se...

Matt

Not heard of it before.

Asaf Karagila

Were you drunk?

Matt

8:57 AM

Probably. : )

Daniil

heh

How many beginner Go players does it take to change a lightbulb? - None, they don't see ladders.

Williham Totland

Do questions about matrix-based coordinate transformations go here?

Asaf Karagila

Here in the chat? Probably not.

Williham Totland

Well, it feels a bit short for a full-fledged question.

Asaf Karagila

Then you can try.

It's the lack of LaTeX which makes matrices impossible.

Gigili

9:04 AM

Hello, how can I show a negation of a property in LaTeX?

Williham Totland

It's really just a question of wether a torus can have its radius and thickness adjusted separately using matrix transformations.

Daniil

@Gigili \neg ?

Asaf Karagila

@Gigili Huh??

\lnot > \neg :-)

Gigili

Like B and B prim

Asaf Karagila

I am not sure what you are trying to do.

Gigili

9:06 AM

@Daniil Um, not that one .. I don't what it's called =\

Daniil

Can you give us an example of what are you trying to do?

Gigili

$ A=(A\cap B)\cup(A\cap \primB) $

I want to prove this

First one is B, the second one is (M - B)

Asaf Karagila

LaTeX is just a typeset, you cannot "show a negation of a property" in it.

Gigili

Or (S -B)

Daniil

What do you want to typeset tho?

Gigili

9:08 AM

(S-B)

Asaf Karagila

S\setminus B

Daniil

i.imgur.com/Qxeh3.jpg what is this D8

Uh, I really should stop browsing reddit

Gigili

@AsafKaragila Do we have in mathematics something like "van" or "wan"?

Asaf Karagila

Huh?

Gigili

=\

Van diagram

Or something like that

Asaf Karagila

9:21 AM

Venn?

Gigili

@AsafKaragila Exactly, thank you.

According to that, I need to write B prim,

Like this , if B was the white circle

The red part

coset of B?

In LaTeX?

B' ??

Yes :D

Sorry for being extremely silly.

Jonas Teuwen

9:31 AM

Was there someone here that wanted to do a PhD in Louvain-La-Neuve? I have a guy from there sitting in my office :-). So if there are any questions...

Matt

So if I have x_n -> x weakly implies Tx_n -> Tx weakly, where T : X -> Y is a linear map and X,Y are normed spaces, how can I show that T is continuous?

Asaf Karagila

You can force it to be.

Matt

: P

Jonas Teuwen

What does x_n -> x weakly mean?

(to you)

Matt

For all phi in X^*: phi(x_n) -> phi(x)

Asaf Karagila

9:35 AM

It barely gets there... it takes forever!

Matt

I guess I need to do something with phi(Tx_n) -> phi(Tx)...

To show that it's continuous, do I try to show that it's bounded or use the epsilon delta definition?

Jonas Teuwen

Did you already try any of them? :-).

I would suggest that you just try and see if it works, that will help you more. If you get stuck you can ask for help (unless you're already stuck of course).

Matt

I thought I was stuck already.

It's homework so I have basically zero energy to try stuff. Must be psychological.

Jonas Teuwen

Do you know PUB?

Asaf Karagila

The place you go to drink?

Jonas Teuwen

9:48 AM

So then you know that weakly convergent sequences are bounded.

Principle of uniform boundedness.

Matt

@JonasTeuwen I only know Pubs...

Uniform boundedness principle? I tried that already

I don't think it fits here

@JonasTeuwen: Thanks, I'll try again!

Jonas Teuwen

Assume T is unbounded, then there exists a sequence x_n converging weakly to 0 such that ||T(x_n)|| -> infty.

Asaf Karagila

@Matt: If pubs won't do the work, try pubes.

Daniil

kinky

Jonas Teuwen

(And what do you know about convergent real sequences?)

Matt

9:54 AM

@JonasTeuwen I think your previous comment answers the question. Or am I missing something?

Jonas Teuwen

Well, those are bounded hence Tx_n cannot converge weakly.

Matt

I think I'm confused.

Asaf Karagila

Dazed and Confused?

Matt

Possibly.

robjohn

I don't know whether adding a verification as I did in this answer is useful enough to justify the extra length of the post.

Jonas Teuwen

10:03 AM

phdcomics.com/comics/archive.php?comicid=912 great.

Matt

: )

robjohn

@JonasTeuwen sounds about right.

Jonas Teuwen

Damn :D.

Daniil

thecreationnews.com/news/science/…

robjohn

10:18 AM

@Daniil That is hilarious!

Daniil

At first I thought this was not satirical and got really anxious

Matt

: D

Daniil

imgur.com/CqZ1z

Jonas Teuwen

I like this one: thecreationnews.com/…

Matt

That doesn't seem real.

Daniil

10:27 AM

haha

J. M.

@Daniil The author is strangely familiar...

Daniil

8D

Matt

I wonder how the other students cope with all the homework. Maybe I'm just infinitely slow compared to others.

Jonas Teuwen

Well no.

I'm correcting FA homework. They suck mighty at making homework.

You just want to do it right, I suppose.

2

Matt

Do you have the same system as ETH? Need to show "effort" and then get score and if score is high enough be admitted to the exam?

As opposed to getting it right?

Jonas Teuwen

10:35 AM

No. The homework counts for 50%.

No, you want to get it right too :-).

Matt

@JonasTeuwen Yes I do. Very much so. But most of the time the questions are just so many and so difficult that I have to write something to show "effort". It's very depressing.

Here they figured that they can't require people to get it right because the questions are too difficult. So instead of making the questions easier they require you to write something and you get points for it even if it's wrong.

Really, it's hard to find words to convey to you just how depressing it is.

Jonas Teuwen

I can imagine :-).

Daniil

Well, this makes sense to me. Even if you fail they can show your mistakes and might help you better.

But it does sound depressing

Transcript for

$Mathematics$ Mathematics