Mathematics - 2012-07-04 (page 4 of 4)

robjohn

19:00

Which could be expressed as $\binom{n}{2\vphantom{0}}-\binom{n}{1\vphantom{0}}+\binom{n}{0}$

Mr.Anubis

hmmm you got it right I guess

robjohn

Or $\frac{(n-1)(n-2)}{2}$

Mr.Anubis

@robjohn How do you comeup with these solving reasonings?

I always get stuck at problems, dammit!!! :/

robjohn

@MrAnubis working lots of problems and practice. Once you have seen enough problems, you start to make connections.

Matt N.

Didn't people (non-unilaterally) agree on meta that closing questions unilaterally is wrong?

Mr.Anubis

19:06

yeah seems fine justice

@MattN Hi, how're you?

Matt N.

@MrAnubis Hi there, thanks, ok, and yourself?

Mr.Anubis

@MattN ok too , thanks :)

robjohn

@MattN A moderator has a hard time doing anything else.

Matt N.

@robjohn What do you mean?

robjohn

@MattN when a mod votes to close, it closes.

Matt N.

19:08

@robjohn Exactly. That's why mods are only supposed to vote to close if there already are 4 close votes.

robjohn

@MattN where on meta was that discussed?

N3buchadnezzar

@MattN Should not mods have the power to instantly close questions ?

robjohn

@N3buchadnezzar they do :-)

N3buchadnezzar

@robjohn I know, but reading Matt`s message, he seems to want moderators only to be able to close questions after receiving 4 votes.

robjohn

@N3buchadnezzar he said it was discussed on meta. I must have missed that.

Matt N.

19:13

@robjohn Here for example.

@robjohn In particular, Akhil's answer.

bbl

robjohn

@MattN That is in keeping with the MO policy for minimal moderator meddling. However, when something is obviously spam or a duplicate, I don't see why a mod should refrain. They should minimize their meddling, but not be completely inert.

Matt N.

@robjohn Q seems to meddle in $\mu$-almost everything though. But: shrug

robjohn

@MattN That depends on how you define meddling.

Matt N.

19:28

@robjohn I define it to mean do something that I do not approve of.

: )

robjohn

@MattN well, then. You should be quite annoyed with moderators :-)

Matt N.

You bet I am! : )

@robjohn Btw: have you seen my teddy? I thought I'd dropped it around here somewhere...

But I can't seem to find it.

N3buchadnezzar

Check the starred messages =)

robjohn

@MattN Last thing I see from him was this

Matt N.

@robjohn "Soon". Aha. Yeah I saw that. I was being silly, I know he's AWOL again.

But I really need a carrot or a (virtual) hug.

Feeling miserable comes in waves when I prepare for exams.

robjohn

19:35

@tb MattN is missing you :-)

He was active on the main site 3 hours ago. Perhaps he will return with a page.

Gigili

@MattN Especially the new ones?

Matt N.

@robjohn I didn't want to ping him because I assume he's got more interesting stuff to do than wasting his time on chat.

@Gigili Not especially. Bill has quite surprised me by being well-behaved. Or at least afaik.

@robjohn If he sees your ping and enters chat it'll fill the "cache" of his mind with chat and he'll lose more than just the time he'll waste in here.

robjohn

@MattN well, now I've pestered him. He can choose to ignore my message in his inbox if he's too busy.

Matt N.

@robjohn True dat. OTOH, people can be quite weak. : )

robjohn

@MattN I won't tell him you said that.

Matt N.

19:38

@robjohn I didn't mean anyone in particular : )

I shouldn't be here either. I should be studying.

Gigili

@MattN Well, you always disagree with me!

Matt N.

@Gigili Not on purpose, I can assure you : )

user19161

@MattN Hugs

user19161

@MattN Good luck for the exam.

Gigili

19:55

@MattN Good, good.

Matt N.

20:40

Good night.

user19161

21:11

@MattN I see you don't like my hugs. :-(

2

Mariano Suárez-Alvarez

21:39

Questions that are very difficult to distinguish from what should be a blog post annoy me muchly... :/

2

anon

hey look it's Mariano!

hmm. @robjohn you there?

user19161

@MarianoSuárezAlvarez Do you mean the question or the answer is very long?

Mariano Suárez-Alvarez

Neither

:)

I mean, when the question is just an excuse to rant about something

you can tell, because in those question nothing is really asked: they are simply assertions

robjohn

@anon Yes. What's up?

Mariano Suárez-Alvarez

(even if there is a question somewhere, to keep with form :) )

robjohn

21:42

@anon whee! I just got 30K :-)

anon

@robjohn earlier in chat we were talking about the EM formula and how it gives a useful asymptotic for the generalized harmonic numbers (basically) and there was a question that you had an answer on you linked to. I want to link to it when I edit when of my old answers.

@robjohn ooooooh

user19161

@robjohn Did you also mysteriously get some rep on old posts just now?

robjohn

@JasperLoy I haven't investigated where it came from. Perhaps I did :-) (and thanks, I assume)

@anon just a sec...

@anon this link?

anon

nono, on MSE

user19161

@MarianoSuárezAlvarez It should be simply much and not muchly there. :-)

anon

21:47

the one that gets $\sum_1^n k^{-s}\sim \frac{k^{1-s}}{1-s}$ via Riemann summation, and then lower terms $\zeta(s)+O(n^{-1/2})$ with Euler-Maclaurin (between the two answers anyway)

Mariano Suárez-Alvarez

It is a poetic licence, dear Jasper

Jordan

well this sucks, I found out if I want to go to college in the US I pretty much can't withdraw from my class

Mariano Suárez-Alvarez

oh nice

my favorite subject

user19161

@Jordan Isn't there a date before which you can withdraw? You exceeded it?

Jordan

I can withdraw Monday, but if I withdraw from another class it will look really bad if I want to go into science/engineering

user19161

21:51

@Jordan Don't worry about looks. Just explain yourself later on.

user19161

And yes I think it is better to withdraw than flunk.

Jordan

@JasperLoy I might be able to get a C, not sure if it is better to get a C or 3 withdraws

user19161

@Jordan Do you need to take this class? Do you think you can do better next time? Consider these.

Jordan

definitely a needed class and I will not do better next time, the teacher is much more difficult next semester

robjohn

@anon Ah, sorry, I had to go afk. let me find it.

user19161

22:01

@Jordan It's a tough decision Jordan. Well, think about it, decide, and don't regret later.

robjohn

@anon perhaps this?

anon

yes that's the one

robjohn

@anon :-)

I have to go get ready for our $4^{\text{th}}$ of July barbeque. I won't be back for several hours.

Independence Day

Jordan

I have to spend all day studying for a class I am going to get a D in, take that England

robjohn

@Jordan England?

Jordan

22:09

fourth of July, we get to celebrate our independence from England

robjohn

@Jordan Ah, I see. Good luck with the exam.

Jordan

Thanks

user19161

@robjohn LOL at the th.

user19161

@Jordan This is calculus right?

Jordan

@JasperLoy Yes

I am really stupid, I pretty much gave up in the class when I get a D on my first test

user19161

22:19

@Jordan Well, first you should stop calling yourself stupid, because all humans are stupid. Do you follow the syllabus or are you having much difficulty with most concepts?

Jordan

@JasperLoy Honestly I think I just need to learn how to study, actually sit down and repeat some task for 4 hours

Peter Tamaroff

@JasperLoy Hey there.

@Jordan I agree with the first thing you said, not the second.

Studying is not repeating a task.

user19161

@Jordan Yes, but for now you need to decide whether to withdraw or not.

Peter Tamaroff

@Eugene I'm getting better at this, or maybe it is just I got some sleep.

user19161

@Jordan Learning to study is an important skill. You need to read with understanding, come up with your own examples and try to see the relation between different concepts.

Peter Tamaroff

22:23

(I hope I am getting better)

Let $u \in f\left(\bigcup_{\alpha \in I} X_{\alpha}\right)$. Then $u=f(x)$ for some $x \in \bigcup_{\alpha \in I} X_{\alpha}$ so that $x \in X_{\alpha}$ for at least one $\alpha$. Then $u=f(x) \in f(X_{\alpha})$ and thus $u\in \bigcup_{\alpha \in I} X_{\alpha}f(X_{\alpha}$

This proves $$ f \left(\bigcup_{\alpha \in I} X_{\alpha}\right)\subset \bigcup_{\alpha \in I} f(X_{\alpha})$$

@anon Hey. How's the $4^{th}$ unfolding?

LOL 9gag.com/gag/4680297

Jordan

I saw that on reddit

Mark Dominus

22:41

I was talking to a guy I am working with in China. I asked where exactly he was. He said "I am in Shanghai. Have you heard of it?"

"Shanghai, hmm… doesn't ring a bell. Is it a big place?"

BenjaLim

@MarkDominus hey

are you familiar with Algebraic topology?

@MattN Hey

You're familiar with Algebraic topology no?

Mark Dominus

I am not very familiar with algebraic topology, only a very little.

I did take a class in it in 1990.

BenjaLim

@MarkDominus Do you have any idea for this: math.stackexchange.com/questions/166543/…

Chris advised to look at just the continuous functions from $X $ to $X$ say that are homotopic to $\textrm{id}_X$

robjohn

@PeterTamaroff I just dropped in while getting ready to leave for our barbeque. That is quite surprising ;-)

NOT

BenjaLim

@robjohn hey

robjohn

22:54

@BenjaLim what's up? I won't be here for long. We have to leave soon

BenjaLim

is it a tradition in the US to clean your barbecue sets after using them?

robjohn

@BenjaLim Yes, but we generally clean by turning it up high to burn off the gunk.

Then a quick scrape or wire brush later.

BenjaLim

@robjohn In australia people don't even bother to clean them :D

That's why I asked if it's standard practice there :D

People in australia are so lazy they don't even bother to clean it

I've been to too many where the hotplate was just black with solidified grease from the previous use

robjohn

@BenjaLim as long as the gunk hasn't grown mold, I guess it's not too unhealthy.

Mark Dominus

I think that is common in the US too.

robjohn

22:58

@BenjaLim ew

Jonas Teuwen

I have been trolling for hours. I need a break.

Hi guys!

Mark Dominus

But there is also a certain fraction of Americans who are pathologically afraid of germs.

robjohn

@JonasTeuwen answer a question. earn your keep :-)

BenjaLim

@robjohn I have had sausages, steak, etc where they smelled of grease

old grease

I dunno why

robjohn

@BenjaLim that doesn't sound appetizing.

BenjaLim

22:58

people just can't be bothered to clean up after making a big mess

@robjohn I guess it's that laid back chilled out attitude

Jonas Teuwen

Basically, that is usually a rationalization the "afraid of germs" usually what comes first is some kind of compulsion to wash hands. One tried to explain this to not sound like an idiot or mentally ill to themselves. So it must be the germs. But really, that is the chicken and not the egg.

BenjaLim

perhaps the one propagated by surfers and stuff

Jonas Teuwen

@robjohn But people do not appreciate my answers. 8-). I like to add a heuristic argument, but that seems to be not-done here.

robjohn

I am cooking at someone else's grill for a couple dozen older people, so I definitely have to clean up

BenjaLim

@robjohn perhaps this movie gives a good idea: youtube.com/watch?v=E0K6lUm5ynw

@robjohn High cholesterol levels with a lot of grease :D

robjohn

23:02

@BenjaLim 2005! that is older than I thought

BenjaLim

@robjohn the movie was set in 1975

@robjohn you live in LA yes?

What kind of shoes do teenagers like to wear there?

robjohn

@BenjaLim yep

BenjaLim

I have a feeling skate culture has had a big impact on what teenagers wear here

robjohn

@BenjaLim I don't know. I wear thongs during the summer.

3

BenjaLim

for example all but finitely many teenagers here wear vans shoes

robjohn

23:04

@BenjaLim there was a Vans store just around the corner here, but it closed recently

BenjaLim

I dunno how even non-skaters like me wear these shoes too :D

robjohn

gotta go, bbl

BenjaLim

bye

Jonas Teuwen

My name is Gollum, and Luke I am your father.

Please, please save me.

I ate his liver with some chava beans and a nice Chianti.

@BenjaLim Are you a consensus taker?

BenjaLim

what da ya mean

Jonas Teuwen

23:09

Hannibal ate a consensus taker his liver with some chava beans and a nice Chianti? I cannot remember. I've seen that movie in the 90's and I was a babeh back then.

user19161

@ben Just a thought. Look at your course syllabus and the contents of the books and decide which to read. IMHO Lee would cover the syllabus in most undergrad AT courses.

Jonas Teuwen

@JasperLoy Is that Justin Bieber?

BenjaLim

@JasperLoy Vigleik told me he wants to cover chapters 1 and 2 of hatcher

Jonas Teuwen

Hatchet versus...

user19161

@JonasTeuwen It was a while ago. I change quite frequently. Depends on what you are seeing. If it is a cute face then it is.

user19161

23:12

@BenjaLim What is the title of the chapters?

BenjaLim

@JasperLoy math.cornell.edu/~hatcher/AT/at1-tc.html

user19161

@BenjaLim I see. Well, then I think Hatcher is probably your best bet.

BenjaLim

I looked at rotman

Jonas Teuwen

I don't wear anything in the summer, so certainly not thongs. Not even things. Yes.

user19161

Sometimes I walk naked at home.

Jonas Teuwen

23:14

I think it is summer as we speak actually. I should follow my own credo. Practice what you preach!

user19161

@BenjaLim Then there is Massey and also Fulton.

BenjaLim

I know

but with so many to choose

best to stick to a few

user19161

@BenjaLim What is wrong with Hatcher? It is your course text and it is the canonical text.

BenjaLim

I think atm hatcher's book is not as gentle for me as rotman say

user19161

@BenjaLim You mean you find the text difficult to understand?

BenjaLim

23:16

At the moment I find it a little sketchy

especially the bit on CW complexes

not a lot of details are given

Jonas Teuwen

I find everything difficult to understand, except what I say myself. What does this mean about me?

BenjaLim

and it's kinda hard for me to imagine what they are

user19161

If you are thinking of Chapter 0, it is not meant to be rigorous.

BenjaLim

@JasperLoy how am I supposed to do exercises at the end of it then?

Jonas Teuwen

Rigor is like so overrated.

user19161

23:17

@BenjaLim After reading the other chapters, maybe.

Jonas Teuwen

Mathematicians just think they are being rigorous but they are not.

user19161

Actually you are not the only one who thinks Hatcher is not good.

Jonas Teuwen

I have to find the first bro that actually can write down their statements in FOL without them having logic as their field! 8-).

user19161

I dislike Hatcher myself, so it is Lee for me, but that's not enough for your course.

user19161

So I would supplement it with Bredon.

BenjaLim

23:19

@JasperLoy me?

How come?

Jonas Teuwen

You guys read like all these books... I am quite illiterate.

user19161

It's just like Evans is the canonical text for PDEs, but I dislike it.

Jonas Teuwen

Because it sucks? Yes. Full of mistakes bro. But that keeps you sharp. But actually it is cool.

I once used it for a very practical application!

BenjaLim

@JonasTeuwen I am told of the legend of evans

user19161

@BenjaLim I mean if I were to seriously study I would use Lee for myself, and supplement it with Bredon.

user19161

23:22

@JonasTeuwen I have not really studied these things really, I just like to compare books.

BenjaLim

Right now I feel a little all over the place

Jonas Teuwen

I mean, you know this right, when you have a table and the floor is not really level of the table sucks?

I mean, like Evans is really thick and has many pages.

user19161

@JonasTeuwen For PDEs, I think Michael Taylor's 3 volumes is God.

Jonas Teuwen

So you can quite accurately make something such that the table does not wiggle so much.

This proves the wide applicability of theoretical methods in functional analysis to real-life problems.

BenjaLim

@JasperLoy learning by one's self is hard

Jonas Teuwen

23:24

Oh yeah. Taylor and his series. Oh, the book guy you mean. Excellent. They are really perfect. They look so cute on your book shelf. Great for visitors! Makes you look like a genius. You also have Bourbaki?

user19161

@BenjaLim Whatever little I know about math, I learn by myself. My courses all sucked.

BenjaLim

@JasperLoy first AT question: math.stackexchange.com/questions/166543/…

user19161

@JonasTeuwen Er, no. Bourbaki makes you look stupid actually.

Jonas Teuwen

So I am doing it wrong? Damn. Why can't I ever do something good.

Is that the reason I can't do mathematics?

user19161

@JonasTeuwen I think you just had some whisky.

Jonas Teuwen

23:25

Some crazy French dudes. I should have listened to Sokal and Bricmont.

No. I just drank water.

BenjaLim

@JasperLoy It's from Rotman

I am going to head off to the library to take another poke at it

Jonas Teuwen

I also like to poke books in the library, it is good fun.

user19161

@BenjaLim OK good luck. Note that Massey's different editions are quite different.

Jonas Teuwen

All these books. What do they learn you? Gibberish. Erdos only had one book. Just think for yourself, the monkeys do the same and they are quite succesful. Did you ever see a monkey read a book? I didn't! And they seem to enjoy life.

user19161

@JonasTeuwen The library that I used to visit, they hid many of the GTMs underground.

Jonas Teuwen

23:28

So no GTM poking uh?

user19161

@JonasTeuwen Teach, not learn. I notice you make this mistake quite frequently.

Jonas Teuwen

@JasperLoy Why didn't you tell me earlier on? 8-). Can you also explain me: why?

When do I use teach and when learn?

user19161

@JonasTeuwen The teacher teaches the student who learns.

Jonas Teuwen

But a book is a dead object.

I learn from the book who is teaching me...?

user19161

So teach and learn are in this sense opposite.

user19161

23:30

@JonasTeuwen Yes, something like that.

Jonas Teuwen

Excellent. Thank you.

user19161

@JonasTeuwen Also, explain to me.

Jonas Teuwen

I don't know where they hide their GTMs. I just order them.

user19161

@JonasTeuwen Also, successful.

Jonas Teuwen

Yes, I knew that...

Err... That's a Dutchism. I know that! 8-).

But! Many Dutch would write: succesfull. So I am already ahead of them.

user19161

23:31

It's weird how many people confuse teach and learn.

Jonas Teuwen

Like succesfull is full of success.

@JasperLoy If it is "many" it is actually not strange. They just copy.

That is how I've learnt English: I copy.

user19161

@JonasTeuwen Yeah, I am wondering whether there is a natural explanation for the confusion.

Jonas Teuwen

@JasperLoy Yes. People are in general morons.

Same problem in Dutch.

But, the morons will win.

user19161

Oh also note I usually use British spellings, not the American ones.

Jonas Teuwen

That is like evolution, you are strange man. You want to spell correctly and stuff... That's bad.

If you put your head above the rest... chop chop!

user19161

23:33

According to my dictionary, whisky is the British spelling, and whiskey is the American or Irish spelling.

Jonas Teuwen

@JasperLoy Is there an American spelling? I was not aware of the fact that there was one. They all seem to write things differently! 8-).

@JasperLoy Your dictionary sucks.

Would you also trust your dictionary on the definition of mathematical terms?

user19161

@JonasTeuwen British and American punctuation differs too. Commas and quote marks are so complicated, ten books will tell you ten different things.

Jonas Teuwen

I think mathematicians are more competent in such things.

user19161

@JonasTeuwen Well, they are for the lay person.

Jonas Teuwen

Yes, I have the Chicago manual of style?

In Dutch we have this "Taalunieversum". These are the dudes that state: you should write it this way. If you do not, it is wrong.

Truely lovely.

user19161

23:35

Ah, the CMS is an authoritative source in American English. Or you can just use Straus's Blue Book at grammarbook.com for AmE.

Jonas Teuwen

In Dutch one can make really cute words. There is also a competition for writing words in Dutch correctly.

user19161

This chat is helping me practise my typing skills.

Jonas Teuwen

I often try. Many times they state this word and you are like: what the bugger monkey is that?

user19161

Now I can type somewhat faster.

Jonas Teuwen

Excellent.

Onomatopeeinflatie. Beautiful word.

user19161

23:36

So your harmonic analysis research is mostly in Euclidean space?

user19161

@JonasTeuwen Onomatopoeia is an English word by the way.

Jonas Teuwen

@JasperLoy Yea. I know. How about "onomatopeeëufemismeinflatie"?

@JasperLoy Well... Not really.

user19161

@JonasTeuwen Nope, that looks German to me.

Jonas Teuwen

@JasperLoy It is Dutch.

It just states: Onomatopoeia eufemism inflation.

user19161

Do you distinguish between "fourier analysis" and "harmonic analysis"?

Jonas Teuwen

23:38

Not really.

I use Fourier analysis when I talk to people that don't know any mathematics.

user19161

Yeah, I guess both can be used for Euclidean space or topological groups.

Jonas Teuwen

Like everybody that does not know what harmonic analysis is.

user19161

It seems that many things which can be done in dimensions 1 and 2 can be generalised to dimension n.

Jonas Teuwen

Yes, but not everything.

There are some odd things. Kissing numbers!

user19161

Breakfast, see you!

Jonas Teuwen

23:41

@JasperLoy It is like only 1:42AM. Craaazy.

Q: "What do you work on?" A: "I work with balls." Q: "Oh! So you are a harmonic analyst!" A: "Uh... A what? I am an urologist."

Transcript for

$Mathematics$ Mathematics