Mathematics - 2012-06-05 (page 5 of 6)

t.b.

21:00

@MattN I used to be. Not so much anymore, but something spectacular like the transit of Venus is something I wouldn't miss.

And we offered a 'scope to a friend of mine who passed his Ph.D. exams recently, so I'd have gone with him. He's very much into it and photography.

Paul Slevin

I would love to see it but

exams

Matt N.

I don't even know what it means : ) And I'm too lazy to look it up.

@tb About the email I sent you the other day: is no answer a yes or are you still making up your mind?

Paul Slevin

venus moves in front of the sun

Matt N.

Don't mean to be a young grasshopper...

@PaulSlevin I see.

Paul Slevin

ooo I'm an established user I didn't even notice!!

Matt N.

21:03

What does it mean?

Paul Slevin

1000 rep

I can see downvotes

Matt N.

Congratulations! : )

Paul Slevin

I answered some daft integral question before I went to bed last night and people were really into it apparently

Thanks :)

Matt N.

: D

Paul Slevin

It's so annoying because I can almost get an enlightened badge (for a different question), but the user has absconded and not bestowed his best answer

Matt N.

21:04

But it's night here. How can you see the venus move in front of the sun? Must be happening tomorrow.

@PaulSlevin Which one? Link pleeze.

t.b.

@MattN If you go to the mountains there's the chance of seeing something early in the morning...

Matt N.

But then I'm asleep! : )

t.b.

@MattN Not entirely sure yet, but a friend of mine from Berlin announced that my Hotel might be needed over the week-end. Sorry. I'm really bad at dealing with emails these days.

Matt N.

@tb No worries about emails. Then I'll hope he'll break his little legs and won't be able to walk to your hotel.

Jonas Teuwen

They even make graduate students teach courses... Not just marking or exercises classes.

Almost the first day they put me in this room with >100 people.

Paul Slevin

21:09

Sorry 2 secondss

13

A: Are isomorphic structures really indistinguishable?

It depends on the structure you are talking about. Isomorphisms are defined to respect a given structure - for example in the category of sets the isomorphisms are just bijections. Any two sets with a bijection between them are virtually indistinguishable - the elements are just labelled differen...

9

A: Integral of$\int_0^1 x\sqrt{2- \sqrt{1-x^2}}dx$

Since you tried to use a trig identity, I'll use one in this solution. Let $x = \sin \theta$ so that $1 - x^2 = 1 - \sin^2 \theta = \cos^2 \theta$, and $\mathrm d x = \cos \theta \mathrm{d}\theta$. Our integral becomes: $$ \int_0^{\frac \pi 2} \sin \theta \cos \theta \sqrt{2 - \cos\theta} \mathr...

Those are the 2

@JonasTeuwen was that not terrifying?

Jonas Teuwen

@PaulSlevin Only slightly.

Five minutes before that I knew they would record it and put it on the web.

t.b.

That's a really enjoyable discussion.

I'd call that a monologue.

Jonas Teuwen

Ah, some good old Cesaro.

Matt N.

Seen it already.

t.b.

I even answered this lazy question because Eugene told me to do so.

Matt N.

21:12

So you always do what you're told?

t.b.

I'm close to deleting everything and voting to close as not a real question. It is difficult to tell what is being asked here.

Matt N.

@JonasTeuwen Yeah, using Silvelight so no one is actually able to watch any of it.

Jonas Teuwen

@tb Hmm, well, it seems like a genuine question to me, it is not that easy.

But the question doesn't show any work, that is true.

@MattN Worked with Mono for me.

Matt N.

Can't be bothered to do anything in order to be able to watch something. It just has to work.

Jonas Teuwen

I agree. I didn't make it.

Matt N.

21:14

: )

t.b.

@JonasTeuwen So you ask the guy if he's got any idea. Obviously he hasn't got any. It's not that easy but parts of it are obvious. Then you give him an outline. No reaction. Then you post a full-fledged answer. No reaction. And the guy's been here over and over again. Lazy bastard.

Matt N.

Then why did you write an answer if he didn't respond to any of your comments?

Jonas Teuwen

@tb 8-). But the answer is of high quality, so you can keep it for someone else?

t.b.

That's what I'm probably going to do...

@MattN As I said, I asked Eugene if I should and he insisted. Shouldn't have followed that opinion. Asking if I should should've been enough indication that I shouldn't.

Paul Slevin

Thank you for the upvote

Matt N.

21:17

Welcome : )

Now you got your badger.

Paul Slevin

another nice answer is in the post now haha

Nimza

Good night to everybody whom I didn't seen

t.b.

@JonasTeuwen Thanks, by the way...

Jonas Teuwen

8-).

Nimza

Tell me please, will a support function of "good sets" (like unit ball) in C[a,b] be continuous?

t.b.

21:23

@Nimza Good evening!

Nimza

@tb hello :)

t.b.

@Nimza what do you mean by good sets like unit ball?

And what's a support function?

Nimza

@tb unit ball at first

t.b.

Unit ball in C[a,b]?

Nimza

@tb yes

Matt N.

21:25

Support function = has compact support?

t.b.

And what's a support function? The function associating the support to a function?

From C[a,b] to the compact subsets of [a,b] with the Hausdorff distance?

Nimza

Support function for the set $M$ is a function $\rho ( \Lambda | M ) = \sup\limits_{x \in M} \langle \Lambda, x \rangle$, $\Lambda$ is from $C^{*}$

t.b.

Continuous in $\Lambda$?

Nimza

yes

t.b.

Well, if $M$ is the unit ball, then this is simply the norm of $\Lambda$. So it is continuous in the norm topology of $C^\ast$.

Nimza

21:28

@tb yeah, like in finite dimensional case (if $M$ is a subset of $\mathbb{R}^k$). That's good

@tb other "good sets" for me are functions $y(x)$ from $C[a,b]$ such that $y(x) \in P(x)$, where $P(x)$ is some continuous convex compact

t.b.

And if $M$ is any bounded subset of $C[a,b]$ then this is the supremum of uniformly bounded Lipschitz functions, hence Lipschitz with respect to the norm.

So it is always continuous for bounded $M$.

Eugene

yikes

t.b.

yikes what?

Eugene

i gave my students my email address today

t.b.

bad idea.

Eugene

21:31

i know

oh man

Paul Slevin

have you got unsolicited mail

Eugene

that was really stupid of me

depends what you mean by unsolicited

Matt N.

Fan mail? Or hate mail?

Eugene

question mail

Matt N.

Isn't that what you're being paid for?

Eugene

21:32

eg: why did i get xx on assignment xx

Matt N.

Oh.

I thought maths questions.

Paul Slevin

:/

Eugene

oh well

spam folder!

t.b.

@Eugene that's what the dice in my crystal ball told me

Eugene

@tb good crystal ball

i was i had consulted it first

you live and you learn i guess.

Zhen Lin

21:34

I get the sense that people here don't complain about grades as much. But that's probably because the examiners are much harder to reach, and there are rules about how to contact them...

t.b.

@Eugene you could also use the magic eight ball for grading.

Paul Slevin

it says in the handbook under no circumstances contact the examiners

Eugene

i invented a system called binary marking

if i wasn't empty you'd get full points

and if it was you'd get 0

they told me i'd get fired if i tried that

Matt N.

@tb I was so looking forward. Now I'll have to cry myself to sleep.

@PaulSlevin You have a handbook? : O

Eugene

@PaulSlevin another +1 to cambridge

Paul Slevin

21:36

maths.cam.ac.uk/postgrad/mathiii/handbook.pdf I mean this thing

Eugene

this is why you shouldn't go to shitty schools.

Paul Slevin

The examiners here are like a mysterious group of entities

like the Jedi council, I wouldn't even know how to get in touch with them

Matt N.

: )

Paul Slevin

I think another reason people don't ask about their grades is that they are too traumatised by the exams to care

t.b.

votes please

Nimza

21:39

@tb thank you a lot! but I can't understand, why if $M$ is a set of uniformly bounded Lipschitz functions, then $\sup\limits_{x \in M} \langle \Lambda, x \rangle$ is continuous function of $\Lambda$

t.b.

@MattN I'm terribly sorry. I should know by tomorrow night or Thursday morning.

Matt N.

@tb Don't worry. I'm being silly. Well, with a tiny bit of truth in it. Note that I'm not (at all) criticising your response time. : )

Eugene

why this got downvoted is nonsense. it is a perfectly legitimate answer. whoever downvoted this is just lazy to work it out.

Paul Slevin

+1 from me

t.b.

@Nimza No. What I was saying is: $\Lambda \mapsto \langle \Lambda, x\rangle$ is a Lipschitz continuous function of $\Lambda$. Since $M$ is uniformly bounded, you're taking the supremum of Lipschitz with bounded above Lipschitz constant. Hence the supremum is Lipschitz continuous.

Eugene

21:44

@PaulSlevin thanks. i don't get what's wrong with it. can someone tell me?

Jonas Teuwen

Hmm, students hardly ever mail me, @Eugene :D.

Paul Slevin

If they don't leave a comment why then they probbaly don't have a good reason

Eugene

@JonasTeuwen lucky you. =(

Jonas Teuwen

When they ask such idiotic questions, I would surely let them notice I think it is an idiotic thing to ask.

Stuff like: "plz giev me all solutiosn to ch 7".

Then I CC the director of education in the reply.

Eugene

@PaulSlevin oh well as long as it's not wrong. i hope my knowledge of linear algebra hasn't decayed THAT much.

@JonasTeuwen the problem is the canadian higher education system is not as critical of its students

Jonas Teuwen

21:46

Neither is the Dutch, but I like at least some respect.

Eugene

every tutorial section i get question to the effect of "what's the answer to question xx"

Jonas Teuwen

I'm not their drinking brother, that one could write to me in that way 8-).

Eugene

and most of the time it's not even to the effect. they ask it outright.

Jonas Teuwen

They demand from me a decent reply, then they should write a decent e-mail in proper Dutch (or English).

Eugene

that is good on you.

i wish i could do that.

Jonas Teuwen

21:48

Why can't you?

Eugene

today they were talking so loud i had to yell.

Jonas Teuwen

I asked the director of education and he fully agreed.

Eugene

@JonasTeuwen my instructor gave explicit instructions to be nice to them.

Matt N.

@Eugene Why not just scratch across the blackboard with your fingernails?

Eugene

@MattN cause that would annoy me as well.

Jonas Teuwen

21:48

Well, I don't think he means you should be nice to them if they think this is a children playground.

Matt N.

Sissy : )

Eugene

@JonasTeuwen he's limited my powers to telling them to shut up.

Jonas Teuwen

I would say something like: Ladies and gentlemen, this is not the restaurant. This is on the next floor.

Eugene

politely on top of it

Jonas Teuwen

And if they don't shut up, don't speak until they do.

If they don't kick some out.

That works!

Matt N.

21:50

I'd scratch the board. I'm quite sure if I scratched it a few times even the last one of them would shut it. : )

Eugene

i'm serious. i tried being hard on them. they complained that i was condescending. i got reprimanded for it

Jonas Teuwen

If that still doesn't work, well I don't know. I would just leave.

What?

Eugene

here's what happened.

i was solving examples on the board.

Matt N.

Perhaps you have the wrong attitude and they notice.

Eugene

someone asked me a homework question.

Jonas Teuwen

21:51

Basically I asked our director of education if this was okay to do. He said: Of course, they should have at lease some respect for the lecturer and you did this in the right way.

Matt N.

I've tutored a few classes, too. I've never encountered anything like this.

Eugene

i literally wrote the answer on the board in my examples (unknowingly)

i said you should know this. i did this on the board.

i got reprimanded.

Jonas Teuwen

That sounds stupid.

Eugene

it is.

Jonas Teuwen

I would complain to somebody above the lecturer 8-).

Just some basic social rules, what the...

If you want to be an idiot, fine, but not in my lecture room, now I am the boss for once! 8-).

Eugene

21:52

i told the instructor they were talking the whole tutorial so i told them they should know it because i didn't want to explain it again.

he said you should be nice to the weak students.

needless to say, i am powerless.

Paul Slevin

I have a great fear of having rowdy students

Jonas Teuwen

Oh, something like that. But then he responds to the last statement which is true.

You should of course help the weak students who know when to stfu.

Matt N.

@PaulSlevin What's a rowdy student?

Paul Slevin

ones that mess around and make noise

throw paper planes etc.

Eugene

@JonasTeuwen haha. ah i wish i was in one of those anonymous schools.

Jonas Teuwen

21:54

@PaulSlevin Uh, kick them out?

Eugene

@JonasTeuwen if only!

Paul Slevin

how does one go about that

Jonas Teuwen

I doubt they do not allow you to kick out the people that ruin it for the rest.

Paul Slevin

I imagine saying please leave the room and they just sit there and make me look like an idiot

Eugene

today i was this close to telling the noisy ones to get out of my classroom.

Jonas Teuwen

21:54

@PaulSlevin Something like: Please talk softer, if this is not possible leave the room.

Well, then you call security to remove them.

Matt N.

@PaulSlevin You say: "You there!" point finger at him and give stern look "Please leave this room, as you are disturbing the other students in here who are trying to learn."

Jonas Teuwen

I recon this will only be necessary once...

Paul Slevin

throw the chalk duster at them

Jonas Teuwen

No, you cannot do that.

Eugene

that was EXPLICITLY forbidden

Paul Slevin

21:56

damn.

Jonas Teuwen

Do not use any physical method.

Eugene

seems like it happens often enough!

Paul Slevin

well actually

my friend who does compute science was telling me, he was late for class once, and the lecturer took a complete flaky and got up and shoved them all out the room

Matt N.

: D

Jonas Teuwen

Hmm, I have a button on my desk to lock the doors.

(from the outside)

Matt N.

21:57

Oh noes! How did it get so late again!?

Eugene

@MattN time has a way of doing that.

Matt N.

The aliens again...

But I accidentally slept 9.5 hours last night, maybe that's why I'm not too sleepy.

Paul Slevin

I don't mind if my people are late

I was late for my first ever university class (statistics)

Jonas Teuwen

Neither do I, they can enter from the back door.

Paul Slevin

ahh

Transcript for

$Mathematics$ Mathematics