The h Bar

dmckee

12:14 AM

Comment I want to write: "Double facepalm!"

Comment I actually write: "Algebraic mistake here."

GBeau

12:52 AM

@FenderLesPaul heard anything from ann arbor yet?

ACuriousMind

2:05 AM

@3507: You are an icosahedron again!

3507

@ACuriousMind I always will be.

though this icosahedron is kind of different from a regular one.

I shall be called d30 now instead of d20?

ACuriousMind

@3507 Oh, it's a...triakontahedron?

3507

@ACuriousMind I don't think so, I made it up.

by drawing a large triangle in the centre.

ACuriousMind

So it isn't a thirty-faced polyhedron?

I thought that because you said d30, so that would be a triakontahedron

3507

I know, I was only guessing it had 30 faces.

ACuriousMind

2:11 AM

Ah

So you don't know how many faces you have.

3507

It seems that way.

someday i'll count them.

@ACuriousMind can you help me count?

it has 22 faces from the view on my profile image.

idk how many faces in total that is in 3d.

ACuriousMind

@3507 We all have to count our own faces

3507

2:32 AM

damn I'm hopeless.

Bernard Meurer

@DanielSank I'd never recommend Python for large projects, unless it's a silly one. It's just good to bootstrap the idea and prototyping things quickly

user54412

@user507974 Like what others have said, for actual performance (which is a rare thing most people never have to deal with) it has to be fortran (if you hate yourself and your colleagues), c, or c++

Bernard Meurer

Fortran is the fastest of those tho

user54412

c++ can be as fast as c (our group wouldn't use it otherwise), but you have to cut out all that computer science nonsense like abstraction

user54412

@BernardMeurer just not true

user54412

2:46 AM

fortran compilers haven't been written in many years -- all the existing ones translate to c before compilation anyway

user54412

people who claim fortran is faster are always doing unfair comparisons, because the default compiler options differ between languages

Bernard Meurer

@ChrisWhite from what I gave seen at least. When Brazil began exploring pre-salt oil all the geophysical simulation models/programs had to be done from scratch

They built prototypes in C and fortran and the timing difference was very significant

user54412

the most notorious is fortran assumes without checking that you didn't alias arrays, whereas c doesn't assume this -- both languages can be made to do the other behavior, but you have to tell it

3

dmckee

@BernardMeurer Listen to Chris: he does this stuff for a living. Or ask the couple of other regulars here who also do it for a living.

Bernard Meurer

I'm don't doubt what you're saying, I was just saying what I saw

user54412

2:49 AM

I believe you saw it, I just don't believe their results ;)

dmckee

Fortran isn't going away, but it no long reigns supreme and unchallanged for scientific computation.

Bernard Meurer

@dmckee I never overestimate my position here as a noob, I value what you guys have to say a lot

I just feel like discussion is always fruitful when people aren't dicks

user54412

honestly, most people don't even know to put -Wall or equivalent in their makefile (and plenty don't even use makefiles!), so indeed most programmers miss all the subtleties with compiler options

dmckee

Mine you, I do know at least one person whose does it for a living who swears by fortran to this day. As far as I can tell he's just comfortable with the style.

Bernard Meurer

I'll be honest and say I'm lazy for make files. I have an alias called "makeitright" that just has all the flags I want

guest

2:53 AM

Nobody ever talks about BASIC anymore.

user54412

I'll be perfectly honest, part of my choice of adviser was finding one of the few computational people in the department who doesn't use fortran anymore.

Bernard Meurer

There's also "makeitwrong" that ignores warnings and stuff

user54412

^ cute

dmckee

@BernardMeurer I'm guessing your projects don't involve more than a dozen or so files. After that lazy people use graph-based build tools (i.e. make or scons or whatever).

Seriously, building a big project is not a job for a person. Neither is deciding the right build sequence. These are jobs for a program.

Bernard Meurer

@dmckee they never do, not in C at least

I'll be honest, programming in C is to me like writing in Portuguese

dmckee

2:55 AM

Well, my advice would be to start learning a build tool now if you're going to do any bigger programming.

Bernard Meurer

It's too complicated, has too many rules and I always screw up a semicolon

dmckee

But I wouldn't push you at make which has as many warts as Fortran 77.

Bernard Meurer

@dmckee I know how to use makefiles, I'm just a lazy ass when the code is going to be laying around on my computer

user54412

I was so pleased with myself when I pieced together all the information on the internet to construct a gnu makefile that rebuilt only exactly what was needed based on calls to the actual preprocessor. But in practice no one wants that and we just make clean before any build. ::sigh::

Bernard Meurer

I do feel sorry for whomever tries to decipher what I was doing when I leave my job

dmckee

2:57 AM

@ChrisWhite Oh! Bliss, indeed!

Bernard Meurer

Just my .bashrc has enough magic to make Gandalf have a stroke

dmckee

I have this feeling that a language should have a facility for outputting it's own dependency graph built into it's module system.

Bernard Meurer

@ChrisWhite I love it when makefiles are well built like that. Reminds me of compiling xorg on my calculator ; yikes!

LA is a really cool city from what I saw today

But it's too damn dry

ACuriousMind

@Danu: Someone has the same picture as you :P

guest

Did you go to Hollywood?

Bernard Meurer

3:02 AM

@guest nah I just had some food, bought some girlscouts cookies and walked around the stores

Then I went to the supermarket and bought enough crap to make me have an instant heart attack

user54412

oh wait it's girl scout cookie season?!

user54412

must find thin mints

Bernard Meurer

@ChrisWhite THEY ARE EVERYWHERE

dmckee

@ChrisWhite Yes, the pushers have deployed across the nation.

Bernard Meurer

I got the caramel with peanut butter one

Pretty damn tasty

user54412

3:04 AM

alas no scouts in my area, so I have to be proactive

Bernard Meurer

Even though the little girl told me the thin mints where the bomb

Not in those words tho

guest

@ACuriousMind how can anyone ping that kind of username?

user54412

@BernardMeurer I don't understand how a place can be too dry.

user54412

Too dry for farming perhaps, but I really learned to love the lack of humidity while living in LA

ACuriousMind

@guest "Danu" may be weird, but why shouldn't I ping that?

Bernard Meurer

3:05 AM

@ChrisWhite I come from a land where we have 100% humidity all year long. The air has more water than the water itself down there

Everything is dry to me. My eyes hurt and my nose is crying blood (quite literally)

guest

I meant the profile you linked to @ACuriousMind :)

ACuriousMind

@guest I know you meant the user I linked. I think non-ASCII usernames show up in the autocompletion first, before you have typed anything.

So you ping them by typing just @ and hoping there's not too many of them

guest

I see.

user54412

(I really want to pop into that chat room to see more of those flagged messages. They seem so inpirational)

guest

Seems overly complicated.

Bernard Meurer

3:08 AM

Dammit mobile doesn't show them

ACuriousMind

@ChrisWhite That...doesn't sound good, does it?

3507

what happens if you ping yourself? @3507

Bernard Meurer

Someone print it to me!!!

@BernardMeurer

ACuriousMind

@3507 One can even reference one's own message

Bernard Meurer

Nothing

3507

3:08 AM

it doesn't work...

ACuriousMind

@ACuriousMind See?

3507

cool.

ACuriousMind

@BernardMeurer You can't see flagged messages in any case because you're below 10k, what are you talking about?

Bernard Meurer

Oh, I thought he was referring to the star wall

Nevermind, nevermind

ACuriousMind

flagged != starred

Bernard Meurer

3:11 AM

My brain is kaput okay?

ACuriousMind

No, that's not okay

Bernard Meurer

I flew for 20 hours today ;-;

user54412

anyone else always hear != as being shouted in their inner voice?

ACuriousMind

@ChrisWhite It's shouting "not"?

user54412

basically

3507

3:12 AM

it's not even caps.

Bernard Meurer

It's shouting "It's not" to me

At least it's not in italics

user54412

!=

FenderLesPaul

@GBeau yes I got in

Bernard Meurer

What did you just call me @ChrisWhite?

3507

@ChrisWhite kind of now.

Bernard Meurer

3:13 AM

Wanna fight huh?

user54412

@BernardMeurer =!

Bernard Meurer

Bring it irl ill reck u and ur italics

FenderLesPaul

@GBeau I'm waiting on UChicago and Princeton

ACuriousMind

@FenderLesPaul: lol, did you decide you were excited? :P

Bernard Meurer

That's abusive

FenderLesPaul

3:14 AM

I didn't get into Caltech

@ACuriousMind I realized I was somewhat excited :p

so it wasn't an accurate statement haha

3507

I get my offer of admission in may.

because my marks are bad!

FenderLesPaul

@GBeau If I get into UChicago I will be ecstatic because I can meet Bob Wald!

But my top choice is still UCSB so I'm not as anxious as before

ACuriousMind

@FenderLesPaul Only completely hysteric half of the time now? :D

Bernard Meurer

@ACuriousMind his shoulder is exciting

FenderLesPaul

@ACuriousMind I would like to say a third hehe

i.e. I check my email less frequently

and generally feel better about myself

Bernard Meurer

3:16 AM

@FenderLesPaul I'm still completely paranoid 100% of the time

ACuriousMind

That's nice

Bernard Meurer

Check my email some 8 times a day

3507

@BernardMeurer did you get in anywhere?

come to waterloo.

FenderLesPaul

@BernardMeurer hang in there bud!

Bernard Meurer

@3507 Only one that came back already was UIUC which didn't appreciate my magic jokes enough

@FenderLesPaul Working on it. Bought a helmet to be able to hit my head on the wall more safely now

FenderLesPaul

3:19 AM

Unfortunately I have very little motivation to get any work done now :/

user54412

@FenderLesPaul Their loss. Also, neither did I for grad school or postdoc.

FenderLesPaul

@ChrisWhite <3

You got to go to Princeton anyways

which is about as badass as it gets

user54412

that's a new adjective for Princeton

FenderLesPaul

what was your thesis on?

(not that I'll understand any of it)

user54412

usually it's described as "quiet" or "focused" or "a good place to get work done, I guess"

user54412

3:24 AM

@FenderLesPaul MHD simulations in GR, modeling black hole accretion

FenderLesPaul

ooh that sounds pretty sweet, is it online?

Bernard Meurer

Princeton is absolutely badass

user54412

it's not written yet :p

FenderLesPaul

ah

that's fair :p

3507

@ChrisWhite not even 50%?

Bernard Meurer

3:25 AM

Yeah the name of mine is Solving decoherence on quantum computers

It will be written in some 10-15 years

3507

@BernardMeurer I bet you will decide on something else by that time.

user54412

@3507 Well, here is the code method paper. My thesis will be that, plus some more detailed notes, plus some applications of the code.

Bernard Meurer

@3507 when I was four I said I would be a magician

Today I'm going for Computer engineering

I do t change my mind ever

FenderLesPaul

Fancy

3507

@ChrisWhite Cool, too bad I am unable to appreciate it with my subpar gr and programming knowledge.

ACuriousMind

3:28 AM

When I was four I wanted to be a garbage man because they get to ride on the garbage truck. Yeah, I don't know what I was thinking, either.

5

Bernard Meurer

Let's make a crowd funding to get @ACuriousMind a garbage truck

3507

I think I said this before but the most chill job is a dry cleaner.

they literally sit there all day and do whatever they want.

user54412

@3507 It's okay. There are probably no more than 50 people in the world who would fully appreciate it.

3507

I would consider being a dry cleaner after I do my ph.d.

Bernard Meurer

Gotta head to bed now folks, got a long day tomorrow. Going to UCSB in the morning

Night all

FenderLesPaul

3:32 AM

Whaaat?

Dope

Night!

user507974

7:20 AM

@FenderLesPaul can you give me a rough idea of what you were trying to get in with, planning on applying there myself

gonenc

7:45 AM

well look at the book recommendations of my theoretical physics teacher...

user507974

8:34 AM

lol

@gonenc basically if it has a -ik you are good

that being said what level are we talking about, the LL sequence definitely isnt the friendliest for undergraduates

Slereah

9:01 AM

@gonenc Dude loves his Landau

Slereah

10:00 AM

Can all particles interact together

via whatever interaction

Like can neutrinos and photons interact via $\nu + \gamma \rightarrow \nu + e^- + e^+ \rightarrow whatever$

I assume they can, though that's some pretty light interaction

user507974

10:32 AM

@DanielSank I actually learned it pretty well about a week ago (in a grad stat mech course)

Hi ppl

Hello.

Bonjour.

10:48 AM

BO UN JUR

asaa

Is there anyone to help me

!

guest

askaway

asaa

what is eigenvalue of P1/nP1/n operator if we know eigenvalue equation of PP ?

up vote
1
down vote
favorite
If PP is an operator and PΨ=pΨPΨ=pΨ ( pp as the eigenvalue ) then is it true to say P1/nΨ=p1/nΨP1/nΨ=p1/nΨ ( n is an integer and positive number )

1

Q: what is eigenvalue of $P^{1/n}$ operator if we know eigenvalue equation of $P$ ?

If $P$ is an operator and $PΨ=pΨ$ ( $p$ as the eigenvalue ) then is it true to say $P^{1/n}Ψ=p^{1/n}Ψ$ ( n is an integer and positive number )

eigenvalue

Secret

11:37 AM

$$P\Psi=p\Psi$$
Diagonalise P
$$P=UDU^{-1}$$
where $UU^{-1}=I$

Suppose there is $S$ such that
$$S^n=D$$
Then
$$UDU^{-1}=US^nU^{-1}=US^{n-1}SU^{-1}=US^{n-1}ISU^{-1}=US^{n-1}U^{-1}USU^{-1}$$
Thus get the recurrence relation
$$US^nU^{-1}=US^{n-1}U^{-1}USU^{-1}$$
Repeat and use associativity of linear operators
$$US^nU^{-1}=(USU^{-1})^n$$
Thus
$$(USU^{-1})^n=P$$

Since $D$ is diagonal, $S$ is also diagonal, thus the entries $d_{ii}=s_{ii}^n$

Not sure if that will be sufficient to determine that

$$P^{\frac{1}{n}}=USU^{-1}$$ though .... ?

Danu

1:32 PM

@Secret Your "recurrence relation" is trivial: $A B^n C= A B^{n-1} B C$ for every $A,B,C$.

Also note that you cannot necessarily diagonalize $P$ (the spectral theorem gives sufficient conditions)

FenderLesPaul

3:01 PM

@user507974 trying to get in where?

Danu

3:28 PM

3

Q: What is this red corn-like fruit?

I've had these in my garden for years but only saw the inside of one today. I remember seeing something like this in a salad once. What is it, and is it edible?

fruit

Lol

0celo7

Well that was dumb

@DavidZ Mind telling me what that was for or should I just go with the flow

ACuriousMind

@Danu What's funny about someone not knowing what a pomegranate is?

0celo7

@ACuriousMind have you watched The Boondocks?

ACuriousMind

@0celo7 Never heard of it

0celo7

3:46 PM

@ACuriousMind Hmm, you probably wouldn't like it anyway. It's partially a satire of black culture in America...I don't know if a German would appreciate that.

Slereah

Garbage Man - The Simpsons

►

0celo7

You should watch the first episode and report back, @ACuriousMind.

Danu

@ACuriousMind Welp...

FenderLesPaul

@0celo7 look who's back...

0celo7

Back again

0celo7

4:16 PM

How many citations for a paper is considered "good"?

FenderLesPaul

1

0celo7

what if that's your mother

what?

you heard me

fite me irl

4:22 PM

ok

you want my office address?

FenderLesPaul

Nah

Gimme the address to your heart

pats self on back

David Z

@0celo7 here?

0celo7

@DavidZ I don't particularly care.

David Z

Well, it's same thing as always, the dialogue between you and John Duffield becoming inappropriate for this chat room

0celo7

What exactly? AFAIK nothing was deleted, so nothing was flagged.

And I don't understand why he was suspended too.

David Z

4:33 PM

You can't assume that anything flagged gets deleted, and you can't assume that a chat suspension is always triggered by messages that get deleted

0celo7

Uh-oh

You can't say that!

FenderLesPaul

Can we just not talk about this?

Why does it matter?

Let it go.

Danu

Disney's Frozen "Let It Go" Sequence Performed by Idina Menzel

►

SING ALONG, ERR'YBODY!

0celo7

You do know that movie is about irresponsible mentally ill monarchs, right?

user116211

@0celo7: Make a distance from him, always.

0celo7

4:39 PM

@user36790 Impossible.

Danu

@ACuriousMind Did it ever bother you that $h\geq 0$ or even strict inequality is assumed in CFT books, or am I missing something?

@0celo7 The only true kind.

FenderLesPaul

Don't you get ghosts if you have $h < 0$?

Danu

@FenderLesPaul Okay, you can argue in terms of the whole Kac determinant story etc etc

Books always seem to be tacitly assuming it before discussing that, though.

0celo7

What bothers me is that BLT doesn't bother explaining the Kac determinant, monodromy charges or ANY of the "advanced" CFT.

FenderLesPaul

@Danu Ah I see what you're saying

Danu

4:42 PM

@0celo7 That's because B from BLT wrote a book on CFT :P

FenderLesPaul

Yeah I agree it's bothersome

Danu

They have references ya know :P

FenderLesPaul

They make the assumption far too early

0celo7

@Danu No shit.

Ain't nobody got time for another book.

Danu

@FenderLesPaul Yeah, it makes me feel like there is perhaps a model-independent (so not requiring unitarity or anything) way of seeing it.

Especially, actually, because sometimes you can drop such "obvious" HEP-type assumptions in condensed matter theories

FenderLesPaul

4:44 PM

@Danu I've actually been curious of that exact same question i.e. how does one argue for $h \geq 0$ in condensed matter systems?

Unitarity I guess is still valid in that context so maybe the argument involving ghosts in the spectrum still works

but it's not clear to me

Danu

Yeah, maybe...

@0celo7 In any case, why would you expect "serious CFT" in a book that's not about CFT, even if it happens to emphasize the CFT approach to strings?

0celo7

Lack of intelligence.

What kind of answer do you want?

Danu

I guess it was mostly a rhetorical question

Intended to mean "I don't understand why you [...]"

0celo7

@Danu Ok, the answer to your rhetorical question is "Lack of intelligence"

Danu

You seem so bitter lately :\

0celo7

4:53 PM

bitter?

ACuriousMind

@Danu I have never read a CFT book, so no, it didn't bother me :P

Danu

@ACuriousMind ...but perhaps you've taken a course...

John Duffield

@DavidZ : can you point to this "inappropriate dialogue" please? I had a physics discussion, then found myself on a three-day suspension. Meanwhile not-nice comments by other posters have not attracted a suspension.

ACuriousMind

@Danu Yes, but I do not recall us assuming anything about $h$ before showing $h<0$ doesn't have unitary representations.

FenderLesPaul

@Danu he's bitter because he found out he can't grow facial hair

0celo7

4:55 PM

Being a 10 yo girl does have downsides.

Danu

@ACuriousMind Hmkay. So that's right where you guys started off?

ACuriousMind

@Danu No, but where would you need $h\geq0$?

I can't remember any reason one should need that constraint except for unitarity of the rep

Danu

Nothing in particular. It's just that, even before showing that one "reasonably" has $h\geq 0$, the books already only consider such situations

David Z

@JohnDuffield more or less in the first half of this

ACuriousMind

@Danu Well, the point is that there are no situations where $h<0$, so how could they consider them?

Even if you haven't yet seen that this is due to unitarity, such situations just don't occur, so why waste time on them?

Danu

5:02 PM

Then something like "As we will soon see, only models where $h\geq 0$ are physical and hence we will [...]" would be nice.

0celo7

@DavidZ I seriously see NO reason for a suspension there.

That was a civil conversation.

Danu

Is MathJax broken on the site for anyone else?

0celo7

No.

Danu

:(

ACuriousMind

@Danu Yeah, probably. Still, I don't consider it a big deal

David Z

5:05 PM

@0celo7 y'know what, if you want to discuss this I think it's best we take it to another chat room

ACuriousMind

@Danu Works fine here

Danu

@ACuriousMind I guess it's just me then (and @FenderLesPaul).

FenderLesPaul

I stand by @Danu

:)

0celo7

@DavidZ What's wrong with the public administration of justice?

Danu

Oh, it's back for me now too, after about 5 minutes

@0celo7 lmao

EVERYTHING

Lynch mobs and such

ACuriousMind

5:06 PM

I'll get the torches and pitchforks

2

0celo7

If you're worried about embarrassing me -- pretty sure I've said I like boys and am a 10 yo girl.

David Z

It distracts from other conversation. For example ^^

0celo7

@ACuriousMind Hope they're at least decent quality.

Danu

Only the most rusty pitchforks are good enough :)

0celo7

:(

John Duffield

5:11 PM

@DavidZ : Please be specific. I can't see this "inappropriate dialogue" from me. I can see insults from Danu and user36790, who called me insane and who has since compared me with Crothers. I'm nothing like Crothers. And like 0celo7 just said, ours was a civil conversation.

0celo7

@JohnDuffield David invited me to a private chat to discuss my suspension but won't allow you in.

I think there's something wrong with that.

John Duffield

Don't worry about it.

David Z

@JohnDuffield I'll follow up in another room.

If the two of you want to discuss this between yourselves, go ahead, but find somewhere else to do it.

Danu

@JohnDuffield I don't think I wrote any insults. I remember saying (1) that the fact that you're not around as much in chat has been good for the general atmosphere and (2) that many discussions with you have been unfruitful, but that doesn't necessarily mean anything for you personally, just for how I experienced the general interactions between you and others (including myself) in this room.

John Duffield

@DavidZ : OK.

David Z

5:17 PM

ahem not here please

or, at least, not now

Danu

@DavidZ Alright, sorry

John Duffield

@DavidZ : noted.

Jacobadtr

5:30 PM

When normalising a wave function, does my normalisation constant have to take into account the constant from my integration?

It seems like it is impossible to pin down a value if that's the case

ACuriousMind

@Jacobadtr What do you mean? Which integration?

Jacobadtr

@ACuriousMind $\int |\psi (x)|^{2} = 1$ with $\psi (x) = C_2 (\frac{1}{x + \lambda})$. I compute the integral and try to find a value for C_2 that satisfies the normalisation condition, but because my integral is over all x I pick up a constant from the integration

ACuriousMind

@Jacobadtr An integral $\int_{-\infty}^\infty$ does not "pick up a constant from the integration". You're confusing an integral over all of $\mathbb{R}$ with an indefinite integral.

Danu

With the appropriate boundary conditions you should not pick up a constant

Jacobadtr

@ACuriousMind I think you're right. So I am to consider the infinities in the same way as I would an indefinite integral?

ACuriousMind

5:41 PM

@Jacobadtr No. It's an improper integral, not an indefinite integral. The latter gives you an integration constant, the former does not, it is just a number.

What you do is compute $\int_a^b \lvert\psi\rvert^2$ (which is a number dependent on $a$ and $b$) and then take the limits $b\to\infty$ and $a\to-\infty$.

Jacobadtr

@ACuriousMind I meant to say "definite integral", but I see this is an extension of that. Thank you for your help, i'll practice this

GBeau

6:00 PM

that reminds me, I was explaining to somebody how to find $\int _{0}^{\infty} x^{2n}e^{-x^2}\,\mathrm{d}x$ the other day and nobody I was explaining it to had ever seen the trick $$\int _{0}^{\infty} x^{2n}e^{-ax^2}\,\mathrm{d}x =(-1)^n\frac{\partial ^n}{\partial a^n}\int _{0}^{\infty} e^{-ax^2}\,\mathrm{d}x$$

which I use quite often for cheesy integrals

Jacobadtr

That looks very similar to the hint at the bottom of my h/w sheet.

$ \int dx x e^{\gamma x} = \frac{\partial}{\partial \gamma} \int dx e^{\gamma x}$

GBeau

@Jacobadtr it's the same trick, but that integral can be solved with integration by parts just as easily

Jacobadtr

6:15 PM

Yep, that's what I did.