The h Bar

Bernardo Meurer

1:05 AM

Nspire CX Playing Doom on Linux

►

quartata

This needs spam flags:

-2

A: Force of an object "skidding"?

yeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeet @loganpaul.com/shop

0ßelö7

@BernardoMeurer how do we know you're not feeding video through that cable?

Bernardo Meurer

@0ßelö7 Because that's way more work than running Doom, lol

0ßelö7

@BernardoMeurer it seems laggy af

Bernardo Meurer

1:21 AM

It's a calculator

0ßelö7

@BernardoMeurer Skyrim port coming to TI Nspire in 2019

Bethesda getting dat high school math student market

Bernardo Meurer

If it runs on Linux I can get it to run

lol

Does Skyrim run on Wine

If it does it could be possible :P

With a large enough USB drive

0ßelö7

possible?

does the thing even have enough RAM?

Bernardo Meurer

No, which is why we need a large USB

to have a huge SWAP

In fact

We could have many USBs with a RAID-0 swap

:O

It'll probably saturate the USB bus though

0ßelö7

lol

@BernardoMeurer oh god I have to do cubic splines

help

Bernardo Meurer

1:36 AM

Jesus

Run

0ßelö7

@BernardoMeurer can't; have student loans

Sir Cumference

I mentioned the Big Rip to a cosmologist. Got told it was "crackpot science"

0ßelö7

@SirCumference It is.

Sir Cumference

You gotta appreciate the formal term "crackpot" that has arisen in physics

@0ßelö7 Wait, since when have you known about the Big Rip?

0ßelö7

years

Sir Cumference

1:48 AM

Well I mean, the reasons for it being "crackpot science"

0ßelö7

unless you have a regularity condition in your GR claim, I don't believe it

Semiclassical

Here's a question I should know an answer to (motivated by a discussion problem for tomorrow)

0ßelö7

@Semiclassical Ah, you probably know stat mech well, right?

Semiclassical

pretty well

Integration by parts: $$\int_{-\infty}^\infty u(x) v'(x)\,dx =[uv]_{-\infty}^\infty -\int_{-\infty}^\infty u'(x)v(x)\,dx$$

If $uv\to 0$ at infinity then the boundary term doesn't survive.

0ßelö7

@Semiclassical Emulating stat mech, if an operator $A$ has eigenvalues $0\le\lambda_0\le\lambda_1\le\cdots$ (repeated according to the multiplicity), we say that the partition function of $A$ is $Z_A(t)=\sum_{j\ge 0}e^{-\lambda_j t}$. Given $Z_A(t)$, how can I extract the $\lambda_j$'s?

@Semiclassical sounds reasonable

Semiclassical

1:55 AM

To extract $\lambda_0$, take the free energy $ \frac{1}{t}\ln Z_Z(t)$ and note that this goes to $\lambda_0$ as $t\to\infty$.

One can do a similar trick to get the next eigenvalue, but it's not particularly nice.

0ßelö7

what if $\lambda_0$ is repeated?

Semiclassical

hmm

0ßelö7

also I'm not seeing how that's true

is there a log rule for sums I'm forgetting?

Semiclassical

i mean, the basic trick I'm exploiting is that $Z_A(t)\sim e^{-\lambda_0 t}$ for large $t$ since $\lambda_0$ is the smallest positive eigenvalue.

so I guess I missed a minus sign.

Rumplestillskin

Does anyone know if it's possible to get data from a satellite orbit? Or what program can be used to do something like that?

satellite orbit simulation***

Semiclassical

1:58 AM

oh, and I should've had Z_A earlier

0ßelö7

@Semiclassical Hmm...large $t$

Oh, if I multiply by $e^{\lambda_0t}$ and take $t\to\infty$ it should kill all of the terms except for $e^{-\lambda_0t}$

Semiclassical

Right. Same trick.

But that's an easier statement.

Secret

Final plunge of Cassini into Saturn will start on 15/9/2017

0ßelö7

So I have $\lambda_0=\sup\{a\in [0,\infty):e^{-at}Z_A(t)<\infty \text{ as $t\to\infty$}\}$

and then the multiplicity is the value of the limit

Semiclassical

I actually had to deal with a scenario where the eigenvalues $\lambda_k$ could either be real or occur in complex-conjugate pairs, with the first eigenvalue $\lambda_0$ being positive real and having the smallest real part.

0ßelö7

2:01 AM

@Semiclassical Now I redefine the partition function and do the same thing.

Semiclassical

That leads to the 'partition function' having subleading oscillatory behavior with $t$...which is weird.

0ßelö7

ew

Semiclassical

Right.

0ßelö7

@Semiclassical So what about integration by parts?

Semiclassical

If memory serves, it reflected that the system slightly preferring to have a length which was an intger multiple of a certain length scale

right

So we love when we can toss out those boundary terms

And that happens quite a bit in the context of 1D quantum mechanics, since in most of the applications the wavefunction will vanish at infinity.

I'm trying to remember, though, if there's an easy example of where this goes wrong and the surface term survives.

0ßelö7

2:05 AM

@Semiclassical we were talking about this ~1 month ago.

Jul 28 at 1:35, by 0celoñe7

@Semiclassical There are more details than anticipated. The proof goes roughly like this. Using integration by parts one shows that if $\psi\in C^\infty\cap L^2$ and $-\psi''-x^4\psi\in L^2$, then $\psi\in D(H^*)$. One then constructs such a $\psi$ such that $$\langle \psi,H^*\psi\rangle -\langle H^*\psi,\psi\rangle =-\lim_{A\to\infty}[\overline{\psi(x)}\psi'(x)|^A_{-A}-\overline{\psi'(x)}\psi(x‌)|^A_{-A}]\ne 0.$$

Semiclassical

I guess I should clarify: Is there an easy example within common physics applications?

a potential which is unbounded below doesn't really count in that regard.

0ßelö7

@Semiclassical Not "at infinity" but you can put boundary conditions on $[0,1]$ to get stuff

Semiclassical

you mean, like a particle in a box?

if memory serves, that does actually create some issues when one wants to compute $\langle p^2\rangle$ for a particle in a box wavefunction

since the wavefunction vanishes at the boundary but not the first derivative.

so maybe I can mention that.

0ßelö7

@Semiclassical if you define the momentum operator as usual but give the functions the boundary condition $\psi(0)=\psi(1)=0$, the operator isn't self-adjoint

But it is symmetric, so that's neat.

Semiclassical

sounds right.

0ßelö7

2:12 AM

@Semiclassical so unless your kids like functional analysis, that might not be helpful

Semiclassical

heh, no.

0ßelö7

@Semiclassical I find it interesting how we need horrible $L^2$ functions for the math to work out but everyone always assumes the wavefunctions are $C^1$

Semiclassical

nice functions make life easier.

0ßelö7

@Semiclassical when doing beamer and inserting \pause, how do you prevent the editor from spawning 100s of slides and making editing impossible?

Semiclassical

2:27 AM

no idea, i haven't touched beamer in years

0ßelö7

do you use powerpoint?

Semiclassical

it's more than I haven't had to do presentations in quite a while.

something I'd prefer not to get into, tbh

welp, I can't track down the example I was remembering

oh well

Nick Alexeev

0

Q: Peltier "saturation" effects

What happens when a Peltier cooler is unable to maintain the listed gradient because the cooling required is too great? Specifically, if I have a cooler that is rated to provide 1 Watt of cooling when there is a 100C gradient, and it was the only point of heat transfer between two infinite heat ...

0ßelö7

2:47 AM

A for effort

Semiclassical

lol

user400188

what are they trying to fit to?

Sir Cumference

@3075 Is that obe?!

0ßelö7

don't be silly

Sir Cumference

He's literally had that name before

0ßelö7

2:52 AM

@user400188 idk, it's just an example

user400188

Looked like a bad fit to a fibrillating heart.

Secret

chat.stackexchange.com/users/153493/obe

Sir Cumference

@Secret Huh?

3075

yes hello

Secret

o, must be a different one then...

Sir Cumference

2:55 AM

@3075 How was Ireland?

3075

hmmmmmmmm?

Sir Cumference

Didn't you go away?

Someone here told me you were in Ireland

3075

lmao no

0ßelö7

too easy

3075

sorry but you got trolled.

Sir Cumference

2:56 AM

Wait then what happened?

0ßelö7

@3075 did you get good?

Sir Cumference

@0375 Were you Blue?

3075

@0ßelö7 no

it's too early

0ßelö7

@Blue people are talking about you...

3075

actually to tell you the truth I logged into my old laptop and it was on sleep mode on the h bar logged into this account so yeah here I am.

it was unintentional

Sir Cumference

3:00 AM

@3075 He's leaving us again

3075

sorry

I'll come back someday but not right now.

The Bear of Bad News

Hi

3075

also @0ßelö7 do you have any advanced linear algebra book recommendations which is a bit more advanced than hoffman/kunze but not insane? since hoffman/kunze is out of print. asking for a friend.

The Bear of Bad News

@3075 Com on man you gotta stay

3075

oh, who are you?

0ßelö7

3:03 AM

@3075 get a pdf of hoffman-kunze

3075

would that be the best option versus a printed version of a different book?

0ßelö7

I don't know any other linear algebra books

3075

okay I'll let my friend know :p

0ßelö7

what linear algebra could possibly be more advanced than hoffman-kunze

3075

roman?

0ßelö7

3:05 AM

it's 18th century math

@3075 that's esoteric

3075

maybe

The Bear of Bad News

@0ßelö7 Rusty says hi

0ßelö7

@TheBearofBadNews who the hell are you

3075

and why do they keep leaving the room after each message

I'm taking so many courses right now it's ridiculous

I'll probably end up dropping out of a few of the higher ones but I'll attend class anyway for exposure.

Sir Cumference

@3075 Preaching to the choir on that one >_>

0ßelö7

3:09 AM

why can't you just do classes like normal people

3075

because I am an insane dude

0ßelö7

clearly

The Bear of Bad News

@0ßelö7 bear of bad news

0ßelö7

@GPhys i am procrastinating so hard right now that I just started flossing

3075

@SirCumference you're doing 7+ of your uni's more difficult courses in a semester?

0ßelö7

3:11 AM

show-off

3075

anyway I will probably have to commit to only a few in the end due to time but I'll still go to the rest anyway.

Sir Cumference

@3075 Eh, 5 of the more difficult courses

0ßelö7

oh you people

3075

hahaha

okay that does seem like showing off but it doesn't really mean anything

anyone can take a course...

but to ace it is a different story

Sir Cumference

@3075 Yeah :/

0ßelö7

3:12 AM

@3075 are you ready for my list of problems yet?

3075

give me

7 MONTHS

okay bye!!!

0ßelö7

@3075 I will give you 7 months for one of them

3075

do you want to send it now? because my skype is basically dead forever.

Sir Cumference

@3075 ...

3075

i don't have the e-mail or password since I forgot it.

and I signed out

sigh

0ßelö7

3:14 AM

@3075 Show that $\mathscr D(\Omega)$ with the usual LF topology, is separable.

No hints

gl

3075

okay I only know some of those words but sure i'll save it

cya in 7 months!!!

The Bear of Bad News

@SirCumference Who are you??

Sir Cumference

I dunno how to answer that

The Bear of Bad News

Oh wait nvm, you're not him

0ßelö7

@ACuriousMind help, this person is scaring us

3075

3:16 AM

also I forgot @ACuriousMind hi hope you're doing fine

GPhys

@0ßelö7 I still need to finish up what I have of this homework and go to bed

3075

bye

0ßelö7

@GPhys I have to do a cubic spline by hand

in theory I know how to do it

in practice I'd rather take the 0

GPhys

it's due tomorrow morning because somebody convinced the professor to make it due 4 days after it was assigned

0ßelö7

@GPhys sounds like a dilligent student

what are you doing, you lazy [redacted]

Anonymous

3:17 AM

@0ßelö7 What?

0ßelö7

@Blue What?

Anonymous

Which people?

0ßelö7

who?

Anonymous

23 mins ago, by 0ßelö7

@Blue people are talking about you...

Anonymous

24 mins ago, by Sir Cumference

@0375 Were you Blue?

Anonymous

3:22 AM

Oooo

Anonymous

meh

Anonymous

I thought there was some conspiracy going on....boring....:P

Sir Cumference

Blue gets on once obe leaves

Coincidence?

Secret

Conspiracy theory:

As The Past returns, something big will happen in 2020

Perhaps, big enough to finally be able to destroy the Source Code

0ßelö7

@SirCumference obe is Indian

3075

3:37 AM

That is a lie. and I have no idea how you would conclude that. also you made me reset my password on this comp to log in and say this :p

you have it backwards but yeah, bye!

0ßelö7

@JohnRennie time for a benchmark?

John Rennie

Morning :-)

0ßelö7

got worse again

@JohnRennie hi

Anonymous

@0ßelö7 I need analysis (multivariable calculus) halp...

0ßelö7

@Blue why the ellipses

Anonymous

3:51 AM

For differentiability of $f$ why should there exist a function $\phi(h)$ such that $f(c+h)=f(c)+h\phi(h)^{+Ah}$ where $\phi(h)\to 0$ as $h\to 0$ ?

Anonymous

I'm not sure how they got the $+Ah$ stuff up there...

0ßelö7

where are you getting this from?

Anonymous

@0ßelö7 Professor's notes :/ I was absent that day...

0ßelö7

what is $A$?

Anonymous

Trying to decipher it...

Anonymous

3:57 AM

:P

0ßelö7

@Blue are you trying to prove the chain rule?

@Blue c'mon

Anonymous

@0ßelö7 How's chain rule related?

0ßelö7

@Blue I am wondering why you need that

and need to know before I go to bed so I don't worry

vzn

@Rumplestillskin sounds like kerbal space program kerbalspaceprogram.com/en

@0ßelö7 what class is that anyway? Game Development? :P

0ßelö7

@vzn quantum cohomology

vzn

4:02 AM

@0ßelö7 huh, really? what dimension are the splines? what is the application?

0ßelö7

$4-\epsilon$

vzn

@0ßelö7 ok. just remember, "builds character" :P

Downgoat

5:09 AM

I was wondering from a primitive perspective, what is mass, in school we learned it is the 'amount' of something but what is 'amount' when you're talking about things like particles which don't always have mass, things like the photon have zero mass but they exist so what does 'mass' mean. Is it energy?

It seems that mass is basically energy, but Einstein's $e^2=\left(mc^2\right)^2+\left(pc\right)^2$ seems to imply that mass and energy is distinct

John Rennie

5:27 AM

Energy emerges from a symmetry of the action called time shift symmetry. For any system that exhibits this symmetry there is an invariant property that we call the energy.

And the energy is related to the mass and momentum by the equation you cite. This comes from the fact that the norm of the four-momentum is an invariant.

So for any system we have another invariant called the invariant mass, that is the $m$ in your equation. You can regard the invariant mass as being defined by this equation.

@Downgoat I'm not sure I would go along with the statement mass is basically energy. The mass is a property of a system just as the energy and momentum are properties of the system. They are related to each other but are all distinct properties.

Sir Cumference

5:57 AM

@0ßelö7 Honest question. Considering how much you read on your own, have you ever found a math course challenging in college?

user228700

6:11 AM

Hi, everyone :-)

user400188

Hello @Kaumudi.H

user228700

Hi.

user228700

@JohnR: In At The Deep End is dead, eh? Is there any way to retrieve it at all?

John Rennie

@Kaumudi.H chat rooms get suspended if they aren't used for two weeks (or some time interval of that order). If the room still exists we can ask a mod to unsuspend it, or we can just create a new room.

user228700

Ah, nice.

John Rennie

6:16 AM

I tried searching for it and it seems the room no longer exists. So you can just create a new room with the same name if you want.

user228700

@JohnRennie No, no, it does.

John Rennie

Link?

user228700

♦ In At The Deep End

John Rennie

Odd. I wonder why it didn't show when I searched for it. Oh well. As soon as one of the mods appears we can ask them to unsuspend the room.

user228700

OK :-)

John Rennie

6:18 AM

Are you thinking you'd like to restart the questions about physics?

user228700

Yes, but not this week. It will have to be after my exams, which end on next Wednesday, I think.

user228700

I will ask a mod. to unsuspend the room after then, how about that?

John Rennie

Yes, or you could just create a new room.

Good luck with the exams BTW. What exams are you sitting?

@dmckee are you around? I see your avatar is live ...

user228700

@JohnRennie Thanks :-) They start next Monday.

user228700

I'm sitting all of them-ICP, ISE, BEE, Cal., Phy. and EGR.

user228700

6:25 AM

:-)

dmckee

@JohnRennie I'm up for a few minutes with the baby. What's up.

John Rennie

@dmckee can you unfreeze a chat room taht has been frozen due to inactivity?

user228700

Yes, please? _/\_ :-)

dmckee

@JohnRennie Yeah. Which one?

John Rennie

♦ In At The Deep End

dmckee

6:27 AM

Done.

John Rennie

@dmckee Thanks :-)

user228700

Thank you! :-)

dmckee

On a completely unrelated note, I just want to say how much I loathe the abbreviations '+ve' and '-ve'. And also why young people should stay off my lawn.

John Rennie

:-)

user228700

Hehe. Why do you hate those abbreviations?

dmckee

6:28 AM

I can see using them in notetaking. The full words are long, but not on Stack Exchange, please.

user228700

Ah.

dmckee

@Kaumudi.H Just one of those things, I guess. I long since decided not to edit them out, but my finger often itch when I see them.

user228700

Right, right, I understand.

Balarka Sen

+---ve

@dmckee does that #trigger you

user400188

It triggers me, and I don't normally have a problem with it.

dmckee

6:33 AM

::chuckles:: Being a particle guy I prefer the proper Trace=-2 approach to relativity.

user228700

There is no other acceptable way of giving oneself the illusion of being productive whilst procrastinating than by organizing one's bookmarks folders:

user228700

Balarka Sen

I just stick all my bookmarks to my bookmark tab

user228700

Oh, geez!

user228700

Additionally, I also use "sophisticated" tools such as Pocket, lol x'D

John Rennie

6:49 AM

@Kaumudi.H are you on the train yet? Or just killing time waiting for the train?

user228700

@JohnRennie Oh, no, no, my train isn't for another 7 hours!

user228700

I was only joking before for I do have an agenda for these 7 hours, and I'm getting on it.

Jasper

If you have no agenda, you can just talk in this room, lol.

@BernardoMeurer A guy in the math chat uses sick to mean cool, lol.

@3075 Advanced Linear Algebra by Loehr covers the linear algebra of modules and multilinear algebra and can be read after Linear Algebra by Hoffman/Kunze or Linear Algebra by Peter Petersen.

John Rennie

@BernardoMeurer is that related to the code you were trying to compile a few days ago? You got it to work then?

Bernardo Meurer

7:17 AM

@JohnRennie No, That never worked

Protobuf screwed me

John Rennie

I assume you've got some acceleration library working since you've compiled the terminal with it ...

Bernardo Meurer

That's just OpenGL, that's EZ

The problem is OpenCV

That's the POS to compile

Sid

7:43 AM

@JohnRennie just help me with this question. I am unable to understand the question.

Question: Unknown mass of ice melts into water at 0 degrees. In doing so, it gains 1 kg of mass. What was its original mass?

John Rennie

@Sid I'm not sure I understand the question.

Unless it means you have to add some energy $E$ such that if you use $E=mc^2$ the $m$ works out to be 1kg. That seems unlikely though.

Sid

Exactly. That's the point. It doesn't mention about adding any Energy

John Rennie

Well ice won't melt if you add it to water at 0 degrees.

Sid

So.. We add energy so that ice melts?

John Rennie

8:26 AM

@Sid We're just guessing. At the moment the question is nonsensical. There must be a misprint or some other information that you haven't given.

CooperCape

8:47 AM

Okay so is a dual vector space, $V^*$ a set of functions that allows a vector space, $V$ to exist? I'm so confused about this.

Wolfram alpha just says that it's the vector space of linear functions $f:V\to R$ but I'm not quite sure what that entails.

Balarka Sen

@CooperCape I can't parse this line. It's just the set of linear functions $V \to \Bbb R$ with a vector space structure.

You think of each linear function(al) as a vector in this space.

I am not sure what's confusing about that, but feel free to ask

CooperCape

but what does it mean by 'dual vector space'?

Balarka Sen

"The vector space of linear functionals $V \to \Bbb R$"

That's the "dual vector space" of $V$, denoted as $V^*$

CooperCape

is... is that it?

Balarka Sen

@CooperCape Yes.

CooperCape

8:58 AM

I feel like it would be more substantial that that...

but okaay. thanks :p

Balarka Sen

I am not sure why you would think that.

CooperCape

jusss sounds more jazzy I guess.

Balarka Sen

If you want simple things to be complicated that's something I guess.

Mithrandir24601

9:27 AM

@Sid I think (although agree with @JohnRennie that it's a bit of an odd question) all it's looking for is that ice and water have different densities at 0 degrees

ACuriousMind

10:10 AM

@dmckee I'm with you there

Jun 4 '16 at 13:08, by ACuriousMind

Why do people write "+ve charge" or "+ve direction"? They seem to mean "positive", but "+" does not mean "positi", so why do they append the "-ve" to "+" instead of just writing "+ direction", which would be a shorter abbreviation that carries the same meaning?

Anonymous

@Sid lol...you are still thinking about that question ? :P

user228700

10:32 AM

@Blue Say, what's happened to that JEE prep. room that S007 created?

user228700

@JohnR: My train leaves in 3 hours :-( I'm not sure why I have kept on updating you about this piece of information but bear with me, please :-P

John Rennie

Problem Solving Strategies

General chat for high school physics. For MathJax see [here](m...

1

user228700

Nice! :-) I'm glad that it survives...thrives.

John Rennie

The trouble is people keep asking me really hard questions in it :-)

user228700

@JohnRennie I see that :-) It will keep your brain from atrophying, at the very least!

user228700

10:38 AM

I made chocolate cake again, BTW, to take back to college.

user228700

Dang, I do miss Doraemon :-/ Wonder what he's up to, these days.

John Rennie

To eat in case of emergencies e.g. having to eat the YWCA food :-)

user228700

@JohnRennie Yes :-)

John Rennie

My lunch today will be boring. I need to eat healthily for a bit to shed the weight I put on staying with my Mum.

user228700

10:43 AM

Ah, 95 more days.

user228700

@JohnRennie Ah. Apples again?

John Rennie

@Kaumudi.H Haven't decided yet. Not apples though. I'm out for drinks with a friend tonight so I need something starchy to soak up the alcohol. Rice or pasta probably.

user228700

Ah, nice.

user228700

Risotto, then?

John Rennie

Probably. I made my vegetable risotto for my Mum while I was staying with her, and she was actually quite impressed.

user228700

10:54 AM

Wow! Nice :-)

user228700

Gah, better do my packing now; I must leave in two hours.

user228700