Mathematics - 2012-05-08 (page 3 of 6)

11:11 AM

When I was in secondary school there was a nine-grade scheme: U for "ungraded" (fail), and (in increasing order) G, F, E, D, C, B, A, A*, where C and above meant "good pass".

I found it quite absurd, since anything less than C would basically be inadmissible for further study.

J. M.

@ZhenLin How ever did they keep track? :o

...and was there a point in being able to tell how much of a failure you are? (i.e. the "underwater" grades)

Zhen Lin

Well, I suppose it must be a leftover from the old days when they merged two (or more...?) separate exam systems. Apparently there was one ("O-levels") for people who intended to continue past the age of 16 and one for people who did not.

I think the "O-level" grades got mapped to the E - A range.

Mind you, the G - D range are still considered pass... at least officially. In school comparison statistics I think it counts as a fail.

J. M.

Yeesh. Grades are one of the things I don't miss seeing from school...

Jonas Teuwen

11:33 AM

@JM Meow?

Ilya

@JonasTeuwen hi

Jonas Teuwen

@Ilya Hi! 8-).

Ilya

@Jonas: it's broken only in the corner, but I have to change the whole glass of course :(

J. M.

Hello Ilya and Jonas. Why does Jonas have whiskers today?

Jonas Teuwen

@Ilya What is broken? :-).

Ilya

11:35 AM

@Jonas: here

Jonas Teuwen

@Ilya Oh how come?

Ilya

dropped it on the floor at home, even the cover didn't save it

Jonas Teuwen

Sucks. What does that cost?

A little less than 200 EUR it seems...

robjohn

@Ilya Is there an Apple Store you can get to?

Ilya

@robjohn hi, 250 EUR there, and 5-10 working days

t.b.

11:38 AM

Haha: Iwan IwanOwitch got balls: O much sorry. But both mathematicians have much research on their keybords.

robjohn

@Ilya Hmm. My son got his fixed for free, but we had AppleCare.

Ilya

@RobJohn that's why I guess

@Jonas: yeah, there is a nodefix center in den Haag, 200 EUR there and 5 days. There is one repair center in Leiden, 150 EUR and 1 day

robjohn

@Ilya You didn't buy AppleCare?

Benjamin Lim

hey any moderator around?

robjohn

@BenjaminLim JM is here

J. M.

11:40 AM

I'm not a mod here... :P

Ilya

@robjohn nope. I thought I'm old enough not to drop it on the floor. I was wrong :(

J. M.

"Certainly, all of calculus is trivial and I can do it even without thinking." - what the ass?

Zhen Lin

My friend just sold his iPad for £200+...

t.b.

@JM Heh, I saw that. Tempted to reply: so is algebraic topology, simplicius

Ilya

@tb the latter comment of him is also nice. Or maybe, the last one

J. M.

11:42 AM

@tb "If I fail I will be deleted." - :D

Ilya

@JM we have a new president now, you know

Jonas Teuwen

This Applecare is way too expensive. You will probably not break your next five iPads 8-))).

Ilya

@Jonas: oh, you're playing with a fire :D

J. M.

@Ilya Oh, not Medvedev anymore?

Ilya

@JM nope, but he maybe will be a new prime-minister

@JonasTeuwen I don't remember how much was it, but it was about a half of price of an iPad

Zhen Lin

11:45 AM

@Ilya A new-old president.

J. M.

Can we have a few hatchets in here?

Jonas Teuwen

Can I haz screwdriver?

Ilya

@JonasTeuwen ?

Jonas Teuwen

Yes, I want to marinate something!

Ilya

@JonasTeuwen ?

Zhen Lin

11:48 AM

??

Jonas Teuwen

Stop mocking my unicorn!

Tara B

@Ilya: About half the price of new iPad. You might actually be able to get a second-hand one for the same price as fixing the screen.

Ilya

@JonasTeuwen ?

@TaraB why do I need it? :)

Jonas Teuwen

@Ilya 8-). Do you know the Ornstein-Uhlenbeck semigroup?

Ilya

@JonasTeuwen quadratisch praktisch gut

@JonasTeuwen not much more that about any Markov semigroup. Why?

Jonas Teuwen

11:50 AM

Bunny will hunt you down and feast on your soul!

@Ilya Okay. I want to prove the contractivity.

Tara B

@Ilya: Well, it might be quicker than getting yours fixed.

Ilya

@JonasTeuwen weak one?

@TaraB how do I know that a new one is ok, ah?

Tara B

@Ilya: Or are you not going to get the screen fixed?

Jonas Teuwen

@Ilya $\|e^{t L} f\| \leq \|f\|$.

J. M.

@TaraB It's the funny thing nowadays: buying a new device is cheaper than having your old one fixed. Jeez.

Ilya

11:52 AM

@JonasTeuwen which norm?

Tara B

@JM: Yes. I dislike it. It's especially noticeable with mobile phones.

J. M.

@JonasTeuwen Screwdrivers don't taste so good, even when marinated...

Jonas Teuwen

@Ilya $L^1(\gamma)$.

@JM Hmm... Then I must pick something else!

Ilya

@JonasTeuwen pick pickles

Jonas Teuwen

Marinated pickles?

Ilya

11:53 AM

@JonasTeuwen yes

@JonasTeuwen it is not done yet?

Jonas Teuwen

But then that bastard Asaf will devour my pickles :-(.

@Ilya It is! But in infinite dimensional spaces 8-)).

(By my advisor)

Ilya

@JonasTeuwen don't worry, he is far away from you

@JonasTeuwen so you want to prove the result proved for infinite-dimensional space for a finite-dimensional case? 0_o7

or it is an exercise?

who the hell has flagged that???

@Jonas: Dynkin has the theorem which gives necessary and sufficient conditions for a linear operator to be a generator of a contraction semigroup

everybody left...

everybody right

everybody, hands up

everybody fight

Jonas Teuwen

@Ilya No, I want an easier proof.

@Ilya I use Hille-Yosida!

Ilya

@JonasTeuwen easier than your supervisor?

Jonas Teuwen

@Ilya Easier than his proof 8-).

Ilya

11:59 AM

@JonasTeuwen the same as in Dynking: based on resolvents

Jonas Teuwen

@tb Do you actually know a strongly continuous semigroup with operator norm strictly smaller than $1$? I have some proof (thanks Markus!) which states this is not possible as you have something like if $M$ is the norm that $\|x\| \leq \frac{M}{\lambda} \|Ax\| + M\|x\|$.

Ilya

render

Jonas Teuwen

So then you send $\lambda$ far far away on an eternal journey.

Benjamin Lim

@JM I wanna delete a question

Ilya

@Jonas: what about taking a strongly continuous $P_t$ and considering $\frac12 P_t$?

Jonas Teuwen

12:02 PM

@Ilya Hmm... There is something missing! 8-).

Ilya

@JonasTeuwen what?

J. M.

@BenjaminLim why can't you do it yourself?

Jonas Teuwen

I don't know.

Benjamin Lim

@JM There are already answers on it

J. M.

@JonasTeuwen Well, it has the legs for walking...

Jonas Teuwen

12:03 PM

@Ilya You get this from $A R(\lambda, A) + \text{stuff} = \text{stuff}$.

J. M.

@BenjaminLim Then that wouldn't be fair to the answerers, no?

Benjamin Lim

well um

@JM could I notify the rest?

Ilya

@Jonas: I better call you - are you in the office?

Jonas Teuwen

@Ilya :-). Yes.

J. M.

@BenjaminLim Yes, you could try asking the answerers...

t.b.

12:06 PM

@JonasTeuwen You mean $\|P_t\| \lt 1$ for all $t \gt 0$?

Ilya

render

Jonas Teuwen

@tb Yes, but I seem to be confused...

@Ilya springerlink.com/content/125602m07m360296

Kannappan Sampath

@JM Is there a way to hammer a CW into all my posts at once?

J. M.

@KannappanSampath None that I know of. So that's why I was seeing those old questions suddenly...

Kannappan Sampath

@JM But, making it a CW bumps posts?

J. M.

12:10 PM

Only temporarily, it seems. They disappear when I refresh the front page.

Kannappan Sampath

Good for me. only 300 posts. It should be over in an hour.

Jonas Teuwen

@KannappanSampath What the? Why would you do that? 8-).

Kannappan Sampath

For fun?

Jonas Teuwen

You're even more wacko than I am. Did one of those monkeys that devoured your biscuits bite you?

Ilya

a strange way of doing fun

J. M.

12:12 PM

I don't believe that's the kind of CW that can be reversed by mods. Be sure you know what you're doing...

t.b.

@JonasTeuwen right now I can only think of boring examples.

Kannappan Sampath

I don't want to reverse that at all. Soon, I'll also write to the mods that my account be deleted. But before that, I'll delete all my comments.

Jonas Teuwen

@tb Yes, under some conditions you can show using the resolvent that $\|x\| \leq \frac{M}{\lambda} \|Ax\| + M\|x\|$ where $M$ is the operator norm?

@KannappanSampath Huh. Why?

Do you have rabies?

Kannappan Sampath

Because this place is full of so many good people. I guess I am not worthy to be a user on this site.

Jonas Teuwen

Hmm... That's a strange reason.

But there are many more idiots than there are many good people!

And you're one of the good people.

Benjamin Lim

12:17 PM

@kahen hey

@KannappanSampath please don't freak out.

Nimza

Hello again!

Kannappan Sampath

@Ben I am not freaking out. But, this time, I am sure about what I am doing.

Benjamin Lim

@KannappanSampath why are you sure?

N3buchadnezzar

Ayhoy thare Landlubbers, ye oldie mate is back again =)

Ilya

@Nimza hi. Did you also get this task?

Jonas Teuwen

12:19 PM

@BenjaminLim I think he got bitten by one of them holy monkeys!

N3buchadnezzar

Anyone want to give me some hints about a flux integral ? Or calculating the flux out of a surface.

Kannappan Sampath

Hmm, the circumstances prevailing in this site lately clearly indicate to me that I am not a worthy user of this site. That I should quit at the earliest possible for the best functioning of this site. So, I'll oblige to the call of the community. I will quit, but I need my own time before I can settle this issue properly.

Nimza

@Ilya hi. первый раз вижу :)

Ilya

@N3buchadnezzar which one? Gauss formula, maybe?

Kannappan Sampath

I may not be able to hammer CW all at once. But i'd finish as quickly I can.

Ilya

12:21 PM

@Nimza говорят, Иван Иванович - распространенное русское имя

Jonas Teuwen

I learnt some Russian yesterday! - Itina hoeij!

But Ilya has explained that it is not a good thing 8-).

N3buchadnezzar

@Ilya I have $F = (x,y,z)$ and need to calculate the flux out of the triangle bound by the coordinate axis and (1,0,0) (0,2,0) and (0,0,3)

Ilya

@JonasTeuwen ah, sorry - I had to escape and I hope it was not rude from my side just to write a translation

Jonas Teuwen

No :-)).

N3buchadnezzar

Pjalsta

Ilya

12:23 PM

use the formula via projections:
$$
\iint x \mathrm dy\mathrm dz+ y\mathrm dz\mathrm dx + z \mathrm dx\mathrm dy
$$

render

N3buchadnezzar

Yeah, I was thinking about using stokes

And do a projection onto the xy plane, does that sound good?

J. M.

Kannappan, I don't know what else to say, but: be sure; think long and hard and be sure that this is what you want.

Ilya

@N3buchadnezzar it does. I mean, the surface suggests to do that, I think

don't forget to calculate the Jacobian - although it's just a determinant of a constant matrix in this case

J. M.

There are only a few worse feelings than regretting something that was entirely done on whim and caprice.

N3buchadnezzar

@Ilya I know, but why the xy plane, I mean would it work if I did it on any other surface?

Jonas Teuwen

12:25 PM

@JM Can holy monkeys carry rabies?

N3buchadnezzar

@JonasTeuwen I do not think a rabbi, would be happy to be carried by anyone. Especially not a holy monkey.

Ilya

@N3buchadnezzar sure, Jacobians would be different and that's it. When you do the projection, you parametrize the surface on another surface (usually on the plane, of course) and then do an integration of the original function on the another surface, paying for this the price of Jacobian

J. M.

@JonasTeuwen Yes, monkeys can be rabid... any mammal can be rabid.

N3buchadnezzar

@Ilya This is all very new to me, thanks a lot for trying to explain it.

Ilya

@N3buchadnezzar I like your trying :D

N3buchadnezzar

12:28 PM

So by stokes theorem I can do a path integral in the xy plane, so this would be a path for example (0,0,0) to (1,0,0) and to (0,2,0)

Ilya

@N3buchadnezzar which stokes theorem do you refer to?

N3buchadnezzar

OH, sorry I forgot there were more..

Jonas Teuwen

@JM But is it common? Say with the ones that come into your kitchen to devour your biscuits! 8-).

N3buchadnezzar

$$ \oint_C F \cdot dr = \iint_R \text{curl} F \cdot \hat{N} ds $$

Ilya

render

Jonas Teuwen

12:31 PM

@Ilya There is this Australian professor (used to be from the Sovjet-Union). He just passed me and said: "Now I know what you like to do in your spare time! Let's do this together one day"

Ilya

@N3buchadnezzar which is in 3d?

Jonas Teuwen

So I was like... What the?

Apparently some guy told him I like to drink 8-).

Ilya

@JonasTeuwen you can only hope for this :) isn't it a supervisor of @BenjaminLim?

N3buchadnezzar

@Ilya Is this not in 3d? In regard to the triangle we sort of have a 2d surface right?

Jonas Teuwen

@Ilya No, he is from Sydney.

Ilya

12:32 PM

@N3buchadnezzar F is 3d or not?

N3buchadnezzar

F is 3d.

Ilya

@Jonas: but who told you about иди на хуй? I guess, not a professor :)

@N3buchadnezzar well, ok. But in your case you don't know $F$, you know only $\operatorname{curl} F = (x,y,z)$, right?

N3buchadnezzar

Opposite

Ilya

ah, so you need to find
$$
\oint\limits_{\partial T }F \mathrm dr
$$
where $T$ is the triangle?

why not to do it directly?

N3buchadnezzar

Yeah, or the problem only asks me to find the fluks out of the surface S.

Where S is the surface made by the triangle.

Ilya

12:36 PM

@N3buchadnezzar ok, write me here an integral you think you're intended to find

N3buchadnezzar

$$ \iint_S F \cdot n = \iiint_T \text{div} F \, \mathrm{d}V $$

Ilya

render

@N3buchadnezzar there are two integral. which of them do you need to find? what is $S$ and what is $T$?

Kannappan Sampath

My group theory tag is completely CW now. Tommorrow I have an exam in probability. So, I'll not be able to spend more time on this. But, atleast this should give the members of the community an indication that this fool is leaving the site, which would be a reason for them to be happy. I am sorry to put you to so much of inconvenience. I'll be done definitely in a few more days. Please bear with me.

2

J. M.

@JonasTeuwen That I have no idea of...

@JonasTeuwen Weren't you bemoaning the lack of drinking buddies many moons ago? This seems like a nice development...

Ilya

12:51 PM

@Kan: what's going on?

t.b.

@JM Is there some recommended action that one should take with edit suggestions such as this one? I copied the comment and posted it to the answer but is this really what one should do? It happened a few times over the last week and I did similar things, but I'm not entirely sure.

J. M.

Well, he misspelled "recommend" the second time... on the other hand, I don't know, it seems what you've done is making the best out of an unideal situation.

t.b.

@KannappanSampath I really wonder how you come to have the idea that people think you are a fool. I'm sure they don't, and I for one certainly do not. You have one conflict with one user that spills over and over again and I find it more tiresome than anything else. I can understand that you're upset, sure, but I think I can also understand the other side.

2

@JM okay, thanks. That's what I thought. Just making sure if there's some ideas out there that one shouldn't do it.

@KannappanSampath In any case I will miss your contributions a lot if you decide to leave. Please take a deep breath and reconsider.

6

Fortuon Paendrag

1:14 PM

@tbee Do you know what precipitated Kannappan's reaction?

skullpatrol

Lack
of
maturity.

Moshe

1:34 PM

Anyone here?

Benjamin Lim

Are there any algebraists around?

Moshe

I'm trying to find the term containing x^3 in the binomial expansion of (3x-2)^10.

I'm a teensy bit confused though.

If I multiply everything out, I end up with 1080x-128, which doesn't contain the power of three anymore.

Did I do it wrong?

homework

Benjamin Lim

@Moshe why don't you post a question

@Moshe let us work carefully

the coefficient of $x^3$ in the expansion is:

or rather let's look at the $x^3$ term

we have:

$\binom{10}{3}(3x)^3\times 2^{10 - 3}$

Tara B

@BenjaminLim: Yes, why?

Benjamin Lim

@TaraB Let $S$ be the following multiplicative set

$S = \{1,f,f^2, \ldots \}$

I want to consider the basis open sets of the Zariski topology so let's assume that $f$ is not nilpotent

Otherwise $S^{-1}A \cong 0$

Now

In Atiyah Macdonald

Tara B

1:40 PM

@BenjaminLim: I was about to say before you started asking your question: although it might depend what sort of an algebraist you're looking for. I do groups and semigroups.

Benjamin Lim

@TaraB Familiar with localisation and the zariski topology?

Tara B

@BenjaminLim: Sadly not really.

Benjamin Lim

ah ok

@TaraB are you postgrad or something?

Tara B

I read a tiny bit of Atiyah Macdonald once, but only because I was using a theorem from it.

Postdoc.

Benjamin Lim

@TaraB May I know where? I'm at ANU

Moshe

1:41 PM

@BenjaminLim - Trying to, it's messing up the two digit exponent.

Tara B

St Andrews (UK). But I'm from NZ and some of my friends did their masters' at ANU.

Benjamin Lim

@Moshe wolframalpha.com/input/?i=Expand%5B%283x+-+2%29%5E%2810%29%5D

@TaraB Ah ok St. Andrews.

@TaraB I'm just next door! Although I got to say that in the Rugby world cup final last year many people here wanted france to win in the final :D :D :D

because you guys knocked us out!

Tara B

I considered doing a summer scholarship at ANU myself, but then didn't really fancy spending the summer in Australia. Too hot for me.

Moshe

@BenjaminLim Ok, I'll go back to studying. That Wolfram isn't all that helpful. It doesn't show steps and I'm kinda unsure what I'm doing wrong.

Benjamin Lim

@TaraB It's not bad in Canberra. Besides this summer it was freezing. Raining and stuff in sydney, devo......

@Moshe that was computed exactly from what I told you above

Tara B

1:43 PM

Yeah, it's always like that. I watched NZ v France in the world cup before that, and all the English people wanted France to win so that England wouldn't have to face NZ next.

Benjamin Lim

@TaraB hahahahahaha

rugby rivalry, thank god not AFL......

Tara B

France did win. =[

t.b.

updated question, i just afraid spidermen know what i do, so i do not say more

Tara B

What do you call 'freezing'?

Benjamin Lim

@TaraB Where are you from in NZ? I know several people from Hamilton, Wellington and Auckland. In fact one of my best friends at school is now living in Tauranga :D

t.b.

1:44 PM

@Moshe Still there?

Benjamin Lim

@TaraB Freezing was like $15^{\circ} c$

Tara B

I'm from West Auckland.

Benjamin Lim

@TaraB ah ok

Moshe

@tb ya

Benjamin Lim

well it was that cold you had to go into the surf in a wetti :(

Tara B

1:45 PM

Yeah, that's certainly cold for Australian summer. Normal for Scottish summer, unfortunately.

Benjamin Lim

@TaraB well you don't exactly do surfing there......

@TaraB I wanted to go for a surf a few times, had to go in a wetti

Tara B

My friend's boyfriend has been surfing here this week, actually.

Benjamin Lim

what???????????????????

t.b.

@Moshe so, I guess you do know the binomial formula?

Benjamin Lim

that's nuts!!!

Tara B

1:46 PM

Yep.

Moshe

@tb You mean n choose k a to the k b to the n minus k?

Benjamin Lim

@TaraB Well in fact my friend asked to go for a surfing trip near byron bay

t.b.

@Moshe yes. So what do you take as a and b in the present case?

Benjamin Lim

@TaraB In fact evans head, all of this is in NSW near the QLD border

Tara B

I don't really see how there can be enough waves. (West Auckland has awesome surf beaches and I've never seen proper waves in the UK.)

Benjamin Lim

1:47 PM

@TaraB UK is not exactly well known for surfing.....

@TaraB Tauranga has got like this massive long beach

Tara B

Well actually, some parts of it are. Cornwall, for example.

Moshe

@tb a = 3x, b = -2, n = 10, k = 3

Benjamin Lim

Mt. Manganui

@TaraB You hear narrabeen in the lyrics of the beach boys song "surfin' usa"

or newport in california or something

no mention of the UK :(

t.b.

@Moshe exactly and you get (10 choose 3) * (3x)^...

can you spell it out completely?

Moshe

10 choose 3 is 120

@tb Spell what out?

Tara B

1:48 PM

I've been to Byron Bay, but we couldn't go in the water because there were thousands of bluebottles.

Benjamin Lim

@tb Come to australia and surf!!!! It'll be uber rad man......

@TaraB Those things are gnarly

I remember once in townsville

t.b.

@Moshe Just the formula I started. Right 10 choose 3 is 120

Benjamin Lim

I was visiting some guy we wanted to go into the water near magnetic island

and they were like no......

t.b.

@BenjaminLim I'm not much of a surfer, but I sure like to hang out on the beach :)

Benjamin Lim

@tb Let me show you the real australia :

Moshe

1:50 PM

@tb Can we move in here? chat.stackexchange.com/rooms/3366/moshe-is-studying

t.b.

sure.

Benjamin Lim

@TaraB Avalon, Sydney

@tb there

Tara B

I might see about learning to surf when I move back to NZ. I could barely swim when I last lived there, so it wasn't really a good idea.

@BenjaminLim: Lovely.

Benjamin Lim

@TaraB Exactly, that's what I miss about being in Canberra

the closest place I believe for the beach is batemans bay

t.b.

@BenjaminLim nice.

Benjamin Lim

1:52 PM

that's like 2 hours away

Matt N.

Come to think of it: seeing as you constantly complain about the weather here, have you ever considered relocating to Australia?

Tara B

@BenjaminLim: Yeah, I guess that's why else I didn't fancy Canberra in the summer. It's not even by the beach.

Benjamin Lim

@JonasTeuwen If you want to know what australia culture is like, you can watch this video here: I believe it depicts quite well what the culture is like around the beaches and stuff of sydney. My friend plays in a band and this is their music video. youtube.com/watch?v=-DolfHRTKho

@MattN Was that at @tb?

Matt N.

@BenjaminLim Of course.

Benjamin Lim

@TaraB yeah but if you do a postdoc at sydney

the beaches at sydney in summer are crowded as hell

oh btw

@TaraB and if you go to the smaller beaches there's a lot of localism which can be a problem

Matt N.

1:54 PM

@JM Haha, simplicity strikes again. : )

Tara B

localism?

Benjamin Lim

@TaraB and in the water you can only swim between the flags and usually it's very crowded. You go out a bit and it's the bodyboarders, out even more the surfers and it's very dangerous due to the risk of colliding with another surfer. I know some guy's dad who was knocked out cold and drowned

SauravTomar

@Moshe ,I was wondering how did you embedd a button to your chat message, whats the code for that?

Tara B

Well yeah, I'm used to only being able to swim between flags, because the West Auckland beaches are dangerous.

Benjamin Lim

@TaraB yeah they don't like "outsiders" who are say not from around narrabeen to go and surf in the water, it's like they wanna reserve the best breaks for themselves

Tara B

1:56 PM

Oh, that's not nice.

Benjamin Lim

@TaraB yeah that's what you gotta do :D

Tara B

@BenjaminLim: How did you put the photo in the chat?

Benjamin Lim

I know some guy who got into a fight with someone else because apparently he took some guy's wave and it was actually a good one

to the right of the box where you type stuff is the "upload" button

user19161

@BenjaminLim Waves are free of charge.