Mathematics - 2016-12-10 (page 3 of 6)

kayak

13:01

Hi from Korea

DHMO

@kayak 아녕하세요

Sophie

@kayak How is the new leader going? Do you like Kim Jong Un better than the last one?

kayak

Hahaha @Sophie

안녕하세요

Sophie

that's a bunch of squares

kayak

My leader is impeached.

DHMO

13:03

@kayak 한국인이에요?

kayak

Court is waiting for her.

Yes I'm I'm the one who was talking to you

DHMO

@kayak 하씨?

kayak

Yes.

DHMO

:o

왜

kayak

So many friends of mine is doing this MSE

haha.

I don't like both kim jung un and the last one.

Alessandro

13:05

When you have your paper Möbius strip cut it along the middle, but first try to guess how many rings you'll get and if they'll be linked together or free @sophie

DHMO

@kayak 이름 왜 달라요?

Alessandro

(Just in case you needed more ways to procrastinate :P)

kayak

My name? @DHMO

DHMO

@kayak 예

kayak

My name is Heonjin Ha. It's same.

Nick name in MSE is kayak

DHMO

13:07

how do you say "nickname"?

kayak

In korea?

DHMO

yes

kayak

별명 or we say 'nickname'

DHMO

I see

@kayak so "이름" is only for the real name?

kayak

Yes.

DHMO

13:09

how do you say "name" in general then?

kayak

what's difference btwn name and real name haha

DHMO

well nick name is also a name

kayak

no korean word for 'general' name. I think.

DHMO

I see

kayak

Oh

for publish area

public area we use 성함

like in Office, in passport

이름 can be used for general one.

DHMO

13:12

What about 성명?

Oh, I have a question about Korean grammar

Secret

DHMO

@kayak in Facebook, "view comments" become "XXX 보기". Why do we use "보기"?

Sophie

this is art

Secret

The boundary of the moebius strip is indeed homeomorphic to a cirlce

DHMO

@Secret a trefoil knot is also homeomorphic to a circle

kayak

13:13

@DHMO haha that's really funny thing

DHMO

@kayak I'm serious

kayak

성명=성함

DHMO

I see

kayak

Are you english origin?

DHMO

no

kayak

13:14

I mean mother toughning adsoifjasopi

bad english

I have

Then do you know 한자?

Secret

Now that I can finally twist the ordinary moebius stripe mentally into the sudanese one, it should not be too hard to visualise the real projective plane

DHMO

@kayak 홍콩사람이에요

kayak

Chiness characters?

Ohhhh

There was MaMa concert in 홍콩

DHMO

안 봤어 :/

kayak

Ok haha

보기 is from 보다=view

maybe 보기=viewing=seeing

DHMO

13:15

모르고 볼 수 없었어

kayak

모르고, and 볼 수 없었어?

DHMO

@kayak so my question is why we use "보기" instead of something like "봅니다"

@kayak yes

Balarka Sen

@Alessandro More interesting questions for procrastination: If you have a knot or a link in R^3 (embedded circle), an orientable surface (2-manifold with boundary) which has that as the boundary is called a Siefert surface. Can you see what the Siefert surface of the Hopf link (google for picture) is? What the Siefert surface of trefoil knot is?

kayak

@DHMO 봅니다=I see=see(command or order to someone)

보기=viewing(noun)

DHMO

why do we use the noun here?

kayak

13:17

lolll

Your question is keen haha

DHMO

maybe "보십시오" should be used?

kayak

You can think like that I know that.

Lollll

DHMO

하씨도 몰라요?

kayak

You r right.

You can think like that, I know that.
I forgot to put colon here

I know that.

보십시오 can be used. It's really good one and very respectful.

DHMO

I mean, 왜 "보기"인 게, 하씨도 몰라요?

just that the noun feels strange

kayak

13:20

I know why they use '보기' instead of '보십시오'

DHMO

you won't say "viewing XX comments"

@kayak why?

kayak

Yes noun feels strange.

I guess : Facebook used translator haha

Alessandro

I don't know what the hopf link or the treefoil knot are @Balarka, I'll look them up later, I'm supposed to be studying numerical analysis now...

Balarka Sen

Ah, sure.

DHMO

@kayak 생각 않아요...

kayak

13:21

And people don't like to use 'long' word.

보기 is short.

Let's see = 보자 is short but not respectful.

보십시오

보십시오 : too respectful.

DHMO

보세요?

kayak

Oh 보세요 is good.haha

You r better than me.

DHMO

what

kayak

Oh.

DHMO

I just started learning Korean 6 months ago lol

kayak

13:23

보기 has 'If you want to see, click this'

보세요 has 'look at this'

DHMO

@kayak 보면?

kayak

보면 = 'if you see

DHMO

so "보기 (싶으면)"?

kayak

Yes!

DHMO

but....

kayak

13:24

You really good

DHMO

we say 보고 instead...

kayak

???

보기 is not that common word.

DHMO

보고 싶으면 o
보기 싶으면 x

kayak

This is why I say Facebook used translator.

Alessandro

To be honest that question sounds more intriguing than numerical analysis though @Balarka

DHMO

13:25

maybe

Balarka Sen

lol.

kayak

보고 싶으면 o
보기 싶으면 x
쏘ㅑㄴ ㅑㄴ 갸홋.

보고 싶으면 o
보기 싶으면 x
This is right.

DHMO

ok

Balarka Sen

It's a good exercise in undertanding Siefert surfaces, yes, @Alessandro

kayak

보기 has implication your thought.

DHMO

13:27

@kayak 하씨 한국말 할 수 있어요?

kayak

당연하지!!

난 한국인이니까ㅋㅋㅋ

이거 읽을 수 있어?

DHMO

@kayak 예

kayak

ㅋㅋㅋㅋㅋㅋㅋ 여기에 얼마나 많은 한국인이 왔었을까?

DHMO

@kayak 어디?

kayak

이 채팅방

this chat room

DHMO

13:30

너만 생각해

@kayak 난 읽을 수 있어

kayak

너만 생각해 : ??

Mike Miller

@Balarka what is

DHMO

여기의 하국인 너만 있는 게 생각해

Balarka Sen

I asked him what the Siefert surfaces of the Hopf link and the trefoil are, @MikeMiller.

Nothing special.

Mike Miller

oh

kayak

13:32

여기의 하국인 너만 있는 게 생각해 : I think you r the only person who is korean here?

DHMO

@kayak yes, can you teach me how to say that properly?

kayak

물론!

But how?

DHMO

well, how would you say that sentence?

kayak

What sentence?

여기의 하국인 너만 있는 게 생각해 this one?

DHMO

예

kayak

13:34

Should I say ... Yeogiui hankukin... like this?

DHMO

No

I think my sentence was clumsy

kayak

Yeogiui hangukin nauman itnungea seang gak hea

DHMO

I mean

kayak

Ahl..

여기에 너만 한국인이라고 나는 생각해.

DHMO

thanks

@kayak "여기" "이리" 같아?

kayak

13:37

not same...

DHMO

어떻게?

kayak

not many words are same haha...

For being a good teacher.

Do I have to say 'it's same'..?

Ok I just tell them.

DHMO

??

kayak

여기 = here. 이리 is not a word.

이리 와= come here.

와=come 이리 to here.

이리 = 이쪽으로=to this direction.

DHMO

일았어

kayak

13:39

이리 와 : not respectful. its an order.

이쪽으로 와 is better.

이쪽으로 오세요 : respectful.

DHMO

이쪽으로 오십시오 lol

kayak

Yes.

good student.

DHMO

thanks xd

@kayak "한국말" vs "한국어", which one do you use?

한국어 재미있어

kayak

Good question.

한국말 is used by forign people.

한국어 is correct

DHMO

lol

kayak

13:42

I guess 한국말 is wrong.

There are words that is not correct but commonly used.

I guess( Im not a languagest) 한국말 is wrong.

DHMO

linguist

kayak

Thanks haha

http://math.stackexchange.com/questions/2052269/has-a-unique-solution-for-the-elliptic-equation-over-special-case-mu-lambda
Is my question is that difficult? No one is interested in my quesiton TT

DHMO

@kayak how do you say "could you XXX"?

kayak

I've learnt 'Could you'='Would you'='Should you' = 해줄수 있어?

DHMO

oh, thanks

kayak

13:48

Could you check this?=점검해줄 수 있어?

Could you do homework? = 숙제 해줄 수 있어?

DHMO

@kayak is it polite to use "너"?

kayak

Not polite.

DHMO

and "나"?

@kayak

kayak

나 is me

DHMO

is it polite?

kayak

13:54

Is 'I' polite?

Idk haha

DHMO

is '나' polite

well, would it be appropriate to say '너' here?

kayak

ah!! '나'is not polite

저 is more polite that 나

It means 'I' samely

DHMO

but can I use '나' here?

kayak

Yes you can

not that unpolite.

DHMO

can I use '너' here?

kayak

13:56

No you can't

It's aggressive.

DHMO

I see

kayak

hahahahaha lol

DHMO

so how would I refer to you?

kayak

님

kayak님

DHMO

하님?

kayak

13:57

Or 하님 Ok

DHMO

하씨 seems too polite

kayak

헌진 님

Not too polite. not more polite than 하님

DHMO

I see

대학생이야?

kayak

grad student

Not that old

haha

DHMO

무슨 대학?

kayak

13:59

Postech.

You can google it.

DHMO

Pohang University of Science and Technology

Pohang University of Science and Technology (POSTECH) is a private research university in Pohang, South Korea dedicated to research and education in science and technology. In 2012-2014, the Times Higher Education ranked POSTECH 1st in its "100 Under 50 Young Universities" rankings. == Introduction == === History === POSTECH was established in 1986 in Pohang, Korea by POSCO, one of the world's leading steel companies, for the purpose of providing advanced education for budding engineers and laying the groundwork for future technological development. The founder of POSCO and the founding chairman...

포항공과대학교

kayak

www.fb.com/hihunjin
If you want you can add me.

DHMO

싫어 xd

kayak

Ok

haha

I have many foreign friends who want to learn Korean.

mercio

I want to because there is this webtoon that noone is translating ;w;

kayak

14:02

@mercio You want to add me?

mercio

I don't use facebook

lol

Balarka Sen

I plan to learn Russian at some point. Whimsical thoughts are harder to turn into reality than cooking it up though.

DHMO

@kayak 한국 어떻게 생각해?

kayak

Sorry but I have to sleep TT

You mean about president?

Alessandro

I considered learning Russian too @Balarka, according to my sister who's studying to become an interpreter it's pretty damn hard though

DHMO

14:07

anything

kayak

I like my country

really safe country isn't it.

I love Korea

Balarka Sen

@Alessandro Ya, so I heard.

kayak

Bye @DHMO

DHMO

bye

Hey-men-whatsup

hellow....

0/

noɥʇʎPʎzɐɹC

14:25

@KajHansen I know.

Mike Miller

14:42

Icelandic seems unnecessarily hard

meow-mix

good morning / afternoon / evening

Alessandro

Hi @meow

Are you learning icelandic? @Mike

Balarka Sen

IIRC Icelanding is by origin Germanic. But I don't know anything much about it.

Mike Miller

nordic

@Alessandro nope

Balarka Sen

ah, ok.

meow-mix

14:56

i'm so confused on this

Alessandro

What's this?

meow-mix

some of @TedShifrin's projective geometry book

only one specific part

Mike Miller

are you trying to use inner products again

meow-mix

??

no it has to do with him representing projective $2$-space with the plane

Balarka Sen

Can you elaborate?

meow-mix

15:05

so umm one second

let me get a snap of this

why is $x_0 = 0$ represented as a diagonal downwards line?

(this is $\Bbb P^2$, with homogeneous coordinates $[x_0,x_1,x_2]$)

mercio

well because $x_0=0$ is the equation of a line so it should be a line

Mike Miller

those are the "lines at infinity"

Alessandro

Can't you choose any line as the one with $x_0=0$?

Balarka Sen

The whole picture is not quite clear to me, but it intersects $x_1 = 0$ and $x_2 = 0$ because that's what happens in P^2: any two lines intersect at a point

Alessandro

Since there's a projective transformation sending the line at infinity into your chosen line

Semiclassical

15:11

Welp, I hope this is the laziest question I see today: math.stackexchange.com/q/2052566/137524

mercio

lol

Alessandro

Let's say the handwriting is better than average? @semi

Balarka Sen

Give that man a cookie for the handwriting.

s.harp

@Semiclassical this question is lazier, isn't it?

Balarka Sen

Doesn't count.

meow-mix

15:22

@mercio obviously....

but this isn't $\Bbb R^2$

Balarka Sen

@meow-mix Of course not. He's just drawing a schematic.

Lines are represented by literal lines in R^2 in a way consistent with the geometry.

meow-mix

ok

Sophie

sigh today is a bad day :(

meow-mix

why?

Sophie

because ISIS is threatening to capture Palmyra

DHMO

15:30

@Semiclassical lazy as in hand-writing the whole question?

You do have a strange definition of lazy

Balarka Sen

Lazy as in putting no effort in making this question fit as per the guidelines in MSE.

He already had the problem handwritten. He just snapshotted it up and didn't even show his efforts on the problems.

That's pretty lazy to me.

Alessandro

And image posts are discouraged since the link might die in the future, which is why questions are supposed to be self contained

Ramanujan

@DHMO hi!

I want some proofs

Astyx

Any proof ?

Sophie

we all do

Astyx

15:41

Does anyone know what motivated the use of Tchebychev polynomials ?

DHMO

255

Q: Proofs without words

Can you give examples of proofs without words? In particular, can you give examples of proofs without words for non-trivial results? (One could ask if this is of interest to mathematicians, and I would say yes, in so far as the kind of little gems that usually fall under the title of 'proofs wit...

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eurocoder

What does an intersection sign between spaces of functions mean? I keep seeing this lately but I don't know what it means! For example, let $\Omega$ be a bounded domain in $\mathhbb{R}^2$. What does $u \in C^1(\Omega) \bigcap C(\overline{\Omega})$ mean?

Ramanujan

meow-mix

can anyone check if my post is sound? math.stackexchange.com/questions/2052560/…

Ramanujan

In (ii) I got how to show,but iam not getting how to do (i)

DHMO

15:44

@Ramanujan If that sequence converges, then $y = \sqrt[n]{f(x) + y}$

$y = (f(x)+y)^{1/n}$

Alessandro

The roots of the Chebyshev polynomials of the first kind are the so called Chebyshev nodes which are used in numerical analysis (polynomial interpolation more precisely), but I don't know anything about Chebishev polynomials apart from that @Astyx

DHMO

@Ramanujan $\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{(f(x)+y)^{(1/n)-1}}{n} \cdot \left( f'(x) + \dfrac{\mathrm dy}{\mathrm dx} \right)$

Astyx

@Alessandro Yes, I was wondering what motivated the study of Tchebychev polynomials in polynomial interpolation and approximation

@meow I agree with koch on his comment

Alessandro

The point of the Chebishev nodes is that they don't have some convergence issues when used for interpolation that other nodes (i.e. equally spaced ones) have

meow-mix

@Astyx that's not my proof

DHMO

15:46

@Ramanujan Also, from $y=\sqrt[n]{f(x)+y}$, we have $y^n = f(x)+y$

meow-mix

@Astyx mine is the one below lol

Alessandro

I can elaborate on that when I return home since I'm on mobile now if you're interested @astyx

DHMO

@Ramanujan So $\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{(y^n)^{(1/n)-1}}{n} \cdot \left( f'(x) + \dfrac{\mathrm dy}{\mathrm dx} \right)$

$\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{y\cdot y^{-n}}{n} \cdot \left( f'(x) + \dfrac{\mathrm dy}{\mathrm dx} \right)$

$\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{y}{ny^n} \cdot \left( f'(x) + \dfrac{\mathrm dy}{\mathrm dx} \right)$

$\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{1}{ny^{n-1}} \cdot \left( f'(x) + \dfrac{\mathrm dy}{\mathrm dx} \right)$

$\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{f'(x)}{ny^{n-1}} + \dfrac{1}{ny^{n-1}} \cdot \dfrac{\mathrm dy}{\mathrm dx}$

Astyx

@Alessandro Yes they limit the runge effect, but historrically why did Tchebychev study these particullarily ? Is it because of their norm is minimal ? How did Tchebychev (or was it even him ?) "know" the roots of these polynomials would give the "best" approximation when interpolating ?

DHMO

@Ramanujan $\dfrac{\mathrm dy}{\mathrm dx}\left( 1 - \dfrac{1}{ny^{n-1}} \right) = \dfrac{f'(x)}{ny^{n-1}}$

$\dfrac{\mathrm dy}{\mathrm dx}\left( ny^{n-1} - 1 \right) = f'(x)$

Astyx

15:49

@Alessandro My question is more about their appearance than what their use is (I know the proofs of why they do approximate well, but I want to know what motivated their study in the first place)

Alessandro

I have no idea about that, they don't teach us much history

DHMO

@Ramanujan $\dfrac{\mathrm dy}{\mathrm dx} = \dfrac{f'(x)}{ny^{n-1} - 1}$

And we're done

Astyx

Yes it's a pity really

Ramanujan

@DHMO yeah,thanks mathemagician

DHMO

you are welcome

Ramanujan

15:53

Some more questions are there to discuss

Why?

Astyx

Does it make sense to say that $\overline {\Bbb Z} = \Bbb Z$ ? Or does convention have it $\overline {\Bbb Z} = \Bbb Z \cup \{-\infty, +\infty\}$ ?

Ramanujan

@DHMO why is it like that?

DHMO

@Ramanujan I do not understand what you wrote

@Astyx no sequence in $\Bbb Z$ converges to $-\infty$ or $\infty$

Ramanujan

$\sin(a,b)\cos(a×b,c)=1

Then, sin(a,b)=1 and cos(a×b,c)=1

DHMO

What does sin(a,b) mean?

Astyx

15:58

I was taught that $\overline {\Bbb R} = \Bbb R\cup\{-\infty, +\infty\}$ (the extended real line) Is that specific to $\Bbb R$ ?

Ramanujan

a , b and c are vectors

DHMO

What does sin(a,b) mean?

Ramanujan

(a,b) means angle between vectors a and b @DHMO

meow-mix

what do you guys think of this tikz figure i made for induction?

DHMO

@Astyx oh, I thought $\overline {\Bbb Z}$ means the closure of $\Bbb Z$ lol

@meow-mix you should start at S(0)

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$Mathematics$ Mathematics