The h Bar - 2017-12-11 (page 4 of 5)

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4:00 PM

>>> a = "the quick brown fox"
>>> b = a.split()
>>> print(b)
['the', 'quick', 'brown', 'fox']

user228700

Hmm, and what about if I want to initiate a list with values that the user inputs? As I understand it, you can't use the for loop to do this, as you would with arrays in C++...

user228700

@JohnRennie Yes, thanks so much! :-)

The quickest way to learn these things is to try it ...

Anonymous

208

Q: Create an empty list in python with certain size

I want to create an empty list (or whatever is the best way) that can hold 10 elements. After that I want to assign values in that list, for example this is supposed to display 0 to 9: s1 = list(); for i in range(0,9): s1[i] = i print s1 But when I run this code, it generates an error or...

user228700

I've tried it before, using loops to initiate an empty list, but it's really weird. So even though lists are mutable, you can't say list1[i]=int(input("Input a number"))

Anonymous

4:01 PM

SO has answers to almost all your question ;)

@Kaumudi.H do you mean take inputs from the user one at a time and concatenate them into a list?

user228700

Yepp. Hmm, so I gotta use the append function, apparently, in loops but not when I am saying something like list[1]='a'...

@Kaumudi.H if you have a list with some length N you can use mylist[i] = xxx for any value of i < N

But you can't create a list using that syntax.

user228700

Right, I can modify an existing list, but can't create one like that.

Yes. Because the ith element of the list doesn't exist until you create it, and you can't modify the value of something that doesn't exist.

user228700

4:09 PM

Right. Gotcha! Thanks! :-D

oh no latex

why are you doing this to me

I loved you like a brother

@EmilioPisanty Doing my usual quick scan back through stuff I missed, and I saw your discussion with giS about a potential expert level physics Q&A site.

@Kaumudi.H so for example this is legal:

>>> for i in range(0,9):
...     a.append(i)
...
>>> print a
[0, 1, 2, 3, 4, 5, 6, 7, 8]

>>> for i in range(0,9):
...     a[i] = i*2
...
>>> print a
[0, 2, 4, 6, 8, 10, 12, 14, 16]

user image

TeX thinks this is on a new page

I'd like to express my thanks for your continuing efforts to make Physics SE interesting enough to attract experts here.

6

You've been doing something concrete (and not easy) on a matter that other people only talk about.

user228700

4:11 PM

@JohnRennie Yes, I understand!

(For those you who don't know what I am on about: check out Emilio's questions tab.‌)

hahaaaaaa fixed it

I am the TeX hacker

user228700

Ugh, working with Python after having done C++ is a pain in the neck.

@Kaumudi.H In what way? I'm primarily a c++ hacker, and I like python.

Anonymous

I'm learning C and Python simultaneously (and had Java in school). Often confuses the hell out of me. SO always comes to the rescue. :)

Anonymous

4:17 PM

Python and C++ is a better combination tbh

user228700

Just the fact that Python uses an interpreter and C++ a compiler. It's...weird, when statements just give outputs without invoking the "print" function.

Anonymous

Both are high level languages

Three is nothing fundamental about a compiler/interpreter difference. I've used a c++ interpreter (Well, without the ability to do templates in the interpreter, though it would talk to external libraries compiled from template code).

I like to think of REPLs as a kind of debugging aid rather that a fundamentally different kind of thing.

Anonymous

Well Python does use a compiler...to convert .py to bytecode...

user228700

Well, I guess it's just annoying to me just 'cause I'm learning to give answers on a test :-/

Anonymous

4:21 PM

@dmckee That is very true

The REPL is just capturing and informing you of the result of expressions as you go along.

kind of like step; print [something] in gdb, but it happens automatically.

I really need someone to take math chats offline for at least a week, cannot stand on having 3 vampires on at the same time

there's an ignore button...

2

@BalarkaSen explain these ODEs to me

which ode

ODE to joy

4:27 PM

@BalarkaSen this one i.gyazo.com/36f1751455e7a9a90290ad2ec47db769.png

I get crazy results with an aggressive control scheme

jfc

@BalarkaSen just f***ing crane?

en.wikipedia.org/wiki/Ode_to_Joy?wprov=sfti1

when you have a 7 equation system your best bet is the computer

@BalarkaSen I am doing the computer

user228700

4:31 PM

@Balarka: Background music to revision:

but I am getting very unphysical results

user228700

user image

user228700

x'D

user228700

Repeated 32 times!

:-D

4:33 PM

I like the version with Hitler in the music video

you like something with Hitler in it?

Perhaps @yuggib could help.

what?

@0celo7 Sure. I like the Downfall meme, for example

Explain

13 mins ago, by 0celo7

@BalarkaSen this one https://i.gyazo.com/36f1751455e7a9a90290ad2ec47db769.png

4:42 PM

@dmckee gee, thanks a bunch =)

2

4:53 PM

@dmckee Congrats :)

arxiv.org/abs/1512.02762

I am not a black hole expert, not sure how good these coordinate invariants are

@Secret That moment a paper sounds really interesting but you don't know enough to validate it...

Margaret has gained a family since this morning! #Oxford #uksnow

Tweeted by DMarshallOcean on December 10, 2017 at 4:51 PM

@SirCumference Thanks. She's five months and a few days old now: strongly opinionated, social, and beginning to be mobile. I'm gaining weight and losing hair and happy as can be.

user228700

@Blue: If you have the tiniest of interest in this stuff: apparently Virat and Anushka just got married.

4:56 PM

@dmckee Oh...I somehow thought that was posted 4 days ago...

But that's great to hear

@Kaumudi.H does anyone apart from the media cares?

@Kaumudi since when are you interested in gossip pseudonews about celebrity scumbags?

user228700

Apparently, yeah; I found out about it 'cause my friends (yeah, plural) posted a status about it.

@dmckee How does she express her opinions? Crying really hard?

@dmckee how can a baby be opinionated

4:58 PM

Inquiring minds want to know :P

user228700

@BalarkaSen Eh, I don't follow this stuff in the slightest-just posting 'cause it'll be everywhere soon enough and like I said, I only got to know about this 'cause my friends posted a status about it on WhatsApp.

ok

@Sid That and reaching for things, batting stuff away, smiling when you do something she likes, giggling if it is extra fun, gaping her mouth if she is hungry, turning her head if you offer food she doesn't want and on an on. Mostly non-verbal stuff.

@BalarkaSen Scumbags?

yeh capitalist scumbags

5:01 PM

If I can't call homophobes idiots I don't think you should be able to call random people scumbags.

@dmckee what is the moderators' opinion on this

I don't speak for moderator in the plural. I'd suggest reining in that language a little.

Dec 6 at 18:42, by John Rennie

For the record, whoever flagged that, homophobia is bigotted, small minded and stupid behaviour and Ryan was quite correct to call homophobes idiots.

I agreed with the idiot comment

Dec 6 at 18:44, by ACuriousMind

@JohnRennie I'm around. Just for the record, don't call people idiots even when it's true, though I've reversed the suspension.

Being a celebrity as such doesn't reflect badly on a person. Even being famous for being famous isn't a crime.

5:04 PM

> even when it's true

+1

Though it is inexplicable to me. People are strange.

according to Stack Exchange Laws, Hitler wasn't an idiot

@0celo7 I'd say "sociopath" rather than "idiot"

Hitler knew Jackson for gosh sakes

Hitler learns Jackson E&M

@SirCumference Oh, talking about mental conditions is even worse!!!!

5:05 PM

@0celo7 That kind of passive aggressive twaddle does not reflect well on you.

@dmckee According to Soviet Russia, it is.

I am making a far left standpoint here

@SirCumference I suspect johnrennie and slereah may knew something about it, as it was on arxiv for two years

and both of them like to work with various spacetime metrics including black holes

@Secret Welp, pinging @JohnRennie and @Slereah in case they're interested

@dmckee Not passive aggressive, just amusing

@bolbteppa that's good but not as good as Hilter and clopen sets

Hitler Learns Topology

5:07 PM

I love that video ^^

I want one with algebraic topology

memory error D:

There's also a meta-video about Bruno Ganz on being memed

I don't think I've seen this one haha

@BalarkaSen yeah, that one is tough

it took me a while to realize that the interview is going on and on about whatever else

5:09 PM

Same

Hitler actor Bruno Ganz interview about Youtube Downfall Parodies

Anonymous

@Kaumudi.H "Just"? My classmates already made memes about it hours ago

user228700

x'D Nice!

Indian memes about Indian celebrities

I shouldn't be surprised these things exist, but still

'friendly set'

5:11 PM

aka a set with $C^\infty$ boundary

@0celo7 it boils my blood to see them

@BalarkaSen ...why?

boils it in the finest communist sense

Anonymous

@Kaumudi.H r/indianpeoplefacebook

are you a self-hating Indian?

5:13 PM

I am not racist

I am hating on capitalism

user228700

@Blue Lol.

@BalarkaSen I can't take you seriously

lol:

> "Who the hell came up with these terms?" -- actually, a German Jew (Georg Cantor) .

> David Snyder So he would indeed have him hunted down and killed by the SS.

dark

how is $C^\infty$ defined on sets

5:18 PM

it's not; what he means is that the boundary is a C^infty submanifold

does that make the set a manifold

an open set is always a submanifold

it's the boundary that's usually not. in this case you say it is, and a nice one too

hmmm

An open set can always be given manifold structure? That's not obvious to me..o.o

An open set of R^n, yes

Every point admits a ball neighborhood

of R^n...where was R mentioned...I must have missed too much of the conversation lol

5:20 PM

it was implied

God "clopen"

the lack of rigor is terrible, I hope it will last

uproxx.files.wordpress.com/2015/06/…

I was thinking like (1,2,3) how u turn that into a manifold...

D:

@enumaris that's a zero-manifold

three points

in space

5:21 PM

haha

floating among nothingness

that doesn't make a manifold tho

Is the space separable or

since u can't map it into open balls can u

@enumaris It does. It's locally homeomorphic to R^0

5:22 PM

@enumaris of course it does

a 0-ball is a point

It's a rather dumb manifold

@BalarkaSen have you learned Morse theory yet?

I need someone to check my argument

only superficially

R^0...hmmm

@BalarkaSen Ok it's a kind of tricky argument using the Morse index

nvm then

5:24 PM

mmkay

I guess if u allow mapping to R^0 then that works...

@0celo7 do you want to briefly explain Morse theory like it was multivariable calculus

tbh closed set sounds more (insert suitable word) than an open set. Are there actually closed sets that contain boundary points that are not limit points

@bolbteppa no

@bolb second derivative test

5:25 PM

From browsing his original paper that's the way he framed it

that's how people think about calculus of variations, yes

Vaguely remember he gives a motivation for applying the SDT globally, no functionals just calculus

but I need a result on the cut locus, which is a kind of tricky object

that's the critical set of exp?

no that's the conjugate locus

5:27 PM

oh

cut locus is that + some more points

@BalarkaSen the practical thing is that the cut locus is where the distance function isn't $C^\infty$

and I'm working with distance functions so I have to care about that

painful

5:56 PM

So the morse lemma seems to be generalizing the idea of a function being concave up or concave down, i.e. being an upward pointing or downward pointing parabola, near a critical point, or a real-valued function of two variables being a saddle etc... near a critical point, by factoring it into a sum of squares where the pattern in the signs (index) tells you what kind of surface it is?

Seems like the proof is just shifting to get rid of the $F(x_0)$ point, then diagonalizing the quadratic form, then proving the law of inertia applies to it or something like that?

Morse lemma is a second order generalization of the inverse function theorem

It tells you upto second order what your manifold looks like at the nondegenerate critical point

(namely, like $\sum \pm x_i^2$)

@BalarkaSen wait did you recommend me bott & tu?

or was it something else

I recommended Guillemin-Pollack

ah

Bott-Tu is a hard book. I think there is a book by Tu on intro to diff top

6:01 PM

i remember seeing a manifolds book

by tu

yeah that

I think that doesn't take much background

you should pick it up

uhhh

and GP?

it doesn't take much background either?

i thought it did because rye was reading it last year

That's interesting, so I guess once you're done analyzing points with non-zero derivative (IFT), you next analyze points with zero derivative and end up with the Morse lemma trying to mimic the IFT in some sense, but it seems like it is copying the whole concave up/down thing from baby calculus more directly than the IFT?

3

Q: Proof of the Morse Lemma in dimension 1

This is the Morse lemma in dimension1 : Let $M$ be a smooth $1$-manifold and $f: M \longrightarrow \Bbb R$ be a smooth function. Suppose $p$ is a non-degenerate critical point of $f$. Then there exists a local coordinate system $(y^1)$ in a neighborhood $U \subset M$ of $p$ with $y^1(p)...

oh well let's keep things interesting

and read a book without background

i love doing that

getting this multi-processing to work is pretty hard it seems

6:11 PM

I read GP two years ago

It doesn't require lots of background but it's a thought-provoking book

ya i'm considering saving it for a lil later

what's a nice book that draws from a lot of areas

wtf, half the time I get a filenotfound error, half the time the thing actually runs

with 0 change to the source code

Berger, "Nonlinearity and Functional Analysis"

baffling...

@0celo7 reading the ToC it looks specialized

6:15 PM

Not at all

like for someone who cares about that stuff

seems like a pretty random thing to learn for me

why is it important?

everyone should care about nonlinear functional analysis

@ooolb lots of nonlinear PDEs out there

sure but

i want something more immediately related to QFT/GR

immediately like at physicist level

those are two subjects which are degenerate at physicist level

i'm working on it

i think geometry is a good place to start

to wash away the "degeneracy"

6:21 PM

wut

i'm playing along with it

Anonymous

@ooolb What type of physics do you do? I never asked...

nothing right now

somebody save me from this multiprocessing fiasco

i did qft and ehhh gr some long time ago

long long time back

Anonymous

6:23 PM

So you're a physics undergrad?

yes

Anonymous

Nice

not really

@enumaris I can give you a problem to work on instead.

@Blue math/phys

Anonymous

6:24 PM

@ooolb Ic...cool stuff

@ooolb just read Reed and Simon

ok i'll reed read and simon

ha

I ain't no maths person

fun

@0celo7 alright

what background do i need?

it's even cheaper now that's weird

I would suggest advanced calculus and measure theory

Anonymous

6:26 PM

I started Reed-Simon without any background. Just use youtube videos along with it or ask balarka for help :P

i'd prefer not to get help right now

Anonymous

Will get back to reading it soon after this exams are over

Why would you ask Balarka about functional analysis?

i need to build character

That actually hurts me.

6:27 PM

@0celo7 i wouldn't

@Blue likes to ignorantly offend people and i don't think he even realizes

Anonymous

I have trouble taking you seriously @0celo7 :P

What does that even mean?

like the fact that you just said that @Blue is enough evidence for me to not want to read anything you post in this chat

combined with other things from before

user228700

@Blue: You around?

Anonymous

@Kaumudi.H Ya

user228700

6:29 PM

:-) Great! Have you studied Classes and Objects in Python?

Anonymous

Little bit...but I got a test tomorrow...not sure if I'll be able to help much

Anonymous

If it's a short question go ahead...

user228700

It's OK, I only have one question.

In any case @ooolb unless you're a complete genius it's impossible to read Reed and Simon without background.

measure theory...

6:30 PM

I figured and I'd rather spend the time right now doing something more productive

And you're missing out on a lot of stuff if you do that

user228700

What is the syntax to declare attributes within a class? Must we use self?

@enumaris what about it?

are you trying to be rigorous with the crazy measures you find in the path integral formulation of QFT?

@enumaris No

6:30 PM

@enumaris me?

it will only lead to tears

You need to be rigorous with Lebesgue measure and spectral measures

and heartbreak

And other measures

Screw path integrals

to be honest i don't really understand how rigour fits into physics

6:31 PM

First of all it's spelled rigor

hey man, path integrals are cool

so what if they are all formally infinite

@0celo7 murican

lmao but i'm saying that

right now i'm on a road to appreciating it

in physics

Maybe it doesn't, but physics isn't all that interesting

Anonymous

@Kaumudi.H This has a detailed discussion: toptal.com/python/…

i don't study anything because it's interesting

idgaf actually

like 5% curiosity the rest is for synesthetic reasons

6:34 PM

@ooolb that's completely wrong

which part

you need to find what interests you 100%

and do that

uhm

sounds like it's not math or physics

it is

because other things

it's like 0.5%

or less

6:35 PM

well my usual solution for that situation is not chat friendly

but you know what it is

i don't actually

hint?

lmao

dude you're not getting it

@BalarkaSen are you there?

I don't particularly believe in having to suffer through a tortured existence

whoah my dude

i like physics/math

it's the only thing i like

i'm just saying i don't like it because i find it interesting

50% of it is interest

the rest is how it looks in my mind when i do it

i like the feeling

Anonymous

...

you're high

6:40 PM

lol.....

Anonymous

@ooolb Sounds like something a masochist would say.

user228700

I looked at the Python Documentation and seem to have understood it for the most part. Thanks anyway! :-) Good luck for the exam tomorrow!

user228700

@Blue: I'm so sorry! My connection died :-/

@Blue explain?

Anonymous

@Kaumudi.H All the best

6:41 PM

because what you just said makes no sense

@0celo7 urggg i did not ever do drugs before

Keep these mind

@ooolb before today?

user228700

@0celo7 @Balarka would disagree :-P

no

a boo

aaaaaaaaaaaaaaa

tbh though!

i'd totally be down to do drugs

but

6:43 PM

@Kaumudi.H Balarka doesn't believe in horable ritualistic suicide? I'm surprised.

idk where to go

to find some

Anonymous

@ooolb Come to my place. I'll get you cheap drugs

no i don't want laced shit

why the fock would i go to india to do drugs

Keep these mind

@ooolb because cheap

Anonymous

@ooolb Great pricing

Keep these mind

6:44 PM

and fake

if i ask around i could probably get some xans in 3 hours from now

@ooolb do it and report back

but i don't really want to

Anonymous

Post a video of yourself as proof.

actual video of @ooolb

NAV - Some Way ft. The Weeknd

6:46 PM

@DavidZ I got pretty close to getting the multi-processing to work (required a few more tweaks) but I've run into a "End of File" error that I don't know how to deal with D:

Keep these mind

with today's newspaper

Anonymous

@Keepthesemind lol

send me your energy!

this isn't real

Poppin xannies

6:47 PM

i was roleplaying someone who was for 5 minutes ironically interested in doing drugs and thought they were funny in doing so

@ooolb please don't do that

it's just annoying

sorry

Keep these mind

@ooolb That doesn't quite cut it.

The Great Dictator - Great Speech for Humanity

where are the computer wizzes...I need help getting rid of this end of file error lol

Anonymous

sleeping

6:54 PM

:(

@enumaris Well, "getting rid of this end of file error" is so vague I can't tell whether I can help you or not :P

it involves multi-processing in python

Keep these mind

make bigger file

I don't think the error actually comes from an end of file

lol

cus I'm grabbing chunks of the file, and I never grab the end chunks

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