The h Bar

ACuriousMind

00:00

Now you're just being dramatic :P

Sir Cumference

@heather Grad school pays, but not much. Having a job earlier would be much better

0celoñe7

@ACuriousMind Now?

He's been bitching on an internet forum for months now.

Emilio Pisanty

@SirCumference don't underestimate the amount of stress and luck-basedness in whatever other alternatives you're considering

heather

@SirCumference ...better...for your wallet? for you, personally? for your general happiness?

ACuriousMind

@EmilioPisanty Already told him life is, in general, a luck-based affair :P

Sir Cumference

00:01

@ACuriousMind I wish I were. There just doesn't seem to be anything redeeming about the field, except for its beauty and importance. But that doesn't seem to matter

Emilio Pisanty

such as e.g. engineering jobs

heather

maybe it's better for your wallet. i don't know about the second question, but it seems like you'd be really happy studying for a PhD.

0celoñe7

@SirCumference What importance?

ACuriousMind

@SirCumference Well, if you have already decided there's nothing redeeming about it, why are talking about this?

rob

@SirCumference It's totally reasonable (and probably advantageous) to work for a few years with a BS before starting grad school. I know several folks who did that. They're mostly financially more comfortable than I am.

Emilio Pisanty

00:02

@SirCumference There's plenty that's redeeming about scientific research as a career. It's just up to you to decide what it is you do and do not value in a career.

Sir Cumference

@heather For children or families I have. I can't live on a very small salary and support them, nor would it be fair to disrupt a child's general happiness for my own

If I get a PhD first and make no use of it, I'd be in a bad situation at a later age

Emilio Pisanty

@SirCumference how so?

Sir Cumference

@EmilioPisanty I'd have paid off my debts by then, and be more employable, if I'd gotten an MS in some other field

0celoñe7

Statistically you're best off if you get an MBA in grad school.

Sir Cumference

@ACuriousMind Sadness D:

I don't know. It's just hitting me

0celoñe7

00:04

@SirCumference You know you're still looking at this the wrong way if money is your objective.

Sir Cumference

@0celoñe7 Money isn't my objective. Financial stability, in its barest form, is my objective...

0celoñe7

The top engineers get paid what, 200k at most?

heather

@SirCumference consider this: if you are really sad about this, and it's clear that you are by the number of times you've come onto this forum to beat your head against a wall about this, then why don't you consider what this decision will do to your health/well-being?

Sir Cumference

@heather I certainly won't be as happy if I didn't learn the physics I wanted. But becoming a physicist and keeping a job is stressful as hell

heather

depends on the job, surely.

Sir Cumference

00:06

@0celoñe7 I'd be fine with far less, but I need to know that jobs are common and I won't be wasting my time waiting for opportunities that I may well be fired from

heather

and, consider that some portion of what you have heard is probably academics grumbling about the worst parts.

0celoñe7

Corporate lawyers are probably more stressed than physicists.

Emilio Pisanty

@SirCumference I would suggest that you consider the possibility that you're just in a downward spiral psychologically, that it is making you less able to consider the pros of a scientific career in an objective fashion, and that it may be wise to hold off from the topic for a few days until you're able to take more objective stock of the possibilities.

2

Sir Cumference

@EmilioPisanty Perhaps...

0celoñe7

@SirCumference Have you been reading Carroll?

Semiclassical

00:07

I'll refrain from commenting, on the grounds that there's a reason I joked earlier that I said my name should perhaps be 'Semicynical.'

Sir Cumference

@0celoñe7 I've been spending the last few days trying to figure out my career, see if I could get the research I'd need to be remotely acceptable into grad school, making sure my grades are fine, etc.

Emilio Pisanty

@SirCumference Or, more to the point, none of the data you've been presented in this conversation has seemed to have any impact on your outlook, which makes me suspect that you may not be in a mood to consider it with due detachment.

0celoñe7

@SirCumference Is your school hard enough that straight As are not expected?

Sir Cumference

@0celoñe7 It seems that the bare minimum is perfection.

@0celoñe7 Definitely. As are prized.

0celoñe7

@SirCumference No matter how perfect you are, there is a Chinese/Indian kid more perfect than you.

ACuriousMind

00:09

::goes back to ponder own existential crisis::

0celoñe7

@Semiclassical Did you read/see/care about what I wrote?

Semiclassical

Haven't looked through it yet. It's a bit removed from what I know about.

What might be more helpful is a clear diagnosis of what goes wrong when the potential is $V(x)=-x^4$.

Sir Cumference

@0celoñe7 And by the way, the reason I felt confident was because I got into a mindset to work hard as hell to get into a field I love. I thought I could do it. Though now it seems luck-based and unstable

I'll take @EmilioPisanty's advice and think a bit. Maybe I'm just panicking

rob

@SirCumference What year are you in undergrad?

Sir Cumference

@rob Sophomore

rob

00:12

@SirCumference You're a Brazilian national in Portugal? Do I remember that right?

0celoñe7

@Semiclassical I'll write a little note on it.

@rob Lol

You confused him with my brother @BernardoMeurer

rob

@0celoñe7 Ah. Ooops.

You people all look alike :-)

0celoñe7

@ACuriousMind do you play any multiplayer games?

Semiclassical

I would imagine a potential that's unbounded below at infinity is going to have problems with self-adjointness.

rob

@SirCumference Your school has a career services office. Talk to them about where graduates from your program have gone.

@SirCumference You have resources to help you make this decision. Use them.

heather

00:14

@0celoñe7 I've been reading about topology like you suggested - it's so cool! I think i understand some of the simple stuff. i found a nice video series i'm watching that's pretty good.

0celoñe7

@Semiclassical No, actually.

If $V\in L^2+L^\infty$, the Hamiltonian is bounded below on the Sobolev space $H^2$.

Sir Cumference

@rob I doubt they'd just say "most don't get a job lol"

Semiclassical

...huh.

rob

@SirCumference Do you think that's true? I think it's not.

Semiclassical

So $-d^2/dx^2-x^4$ is bounded below?

0celoñe7

00:16

@Semiclassical That's certainly not in $L^2$ or $L^\infty$

Semiclassical

Then I'm confused.

0celoñe7

$L^\infty$ means "bounded" in a measure-theoretic sense.

ACuriousMind

@0celoñe7 Lately mostly Dota 2, and occasionally Borderlands 2.

0celoñe7

@Semiclassical Why? I said $V\in L^2+L^\infty$, meaning $V=V_1+V_2$ where $V_1\in L^2$ and $V_2\in L^\infty$.

I wasn't saying iff, I'm just saying there are unbounded $L^2$ functions and the corresponding Hamiltonians are bounded below.

Semiclassical

Ah.

Sir Cumference

00:18

@rob Plus there are only a handful of physics majors who go here. As in, there are more astrophysics profs (about 8 people) than there are astrophysics students

rob

@SirCumference Do you mind to say where?

Semiclassical

But surely a smooth potential which goes to -infty at infinity isn't going to be such an example?

0celoñe7

@Semiclassical Right.

The limit would have to be undefined at infinity, but it could still be unbounded.

Sir Cumference

@rob Yeah, I'd rather not leave a trace of my identity with the stupid things I say here

Semiclassical

I guess this comes down to what we're envisioning as examples, and my carelessness with definitions.

rob

00:19

@SirCumference That's fine, I mostly do the same.

Semiclassical

Plus the word 'smooth' is a pretty strong demand I imagine.

Sir Cumference

@rob Can only mods see full names on someone's profile?

ACuriousMind

@SirCumference Yes, and access to that is logged.

Semiclassical

But anyways. The implication seems to be that $V=-x^4\not\in L^2+L^{\infty}$

Sir Cumference

@ACuriousMind As in, what I write is logged?

Semiclassical

00:21

Or as in "if you look at someone's name, that's logged"

0celoñe7

@Semiclassical Indeed, but as I said that result is not an iff result.

ACuriousMind

@SirCumference As in, there's a trail in the system for each time a mod looks at that information.

Semiclassical

Fair enough.

rob

@SirCumference @Semiclassical Well, both

0celoñe7

The harmonic oscillator is a really nice Hamiltonian but $x^2$ is a "bad" function.

rob

00:21

There's "personally identifiable information" that mods can see. What you store there is recorded, but it's also recorded when a mod looks at it.

ACuriousMind

And yes, since the chatlogs are eternal and public, what you write is also logged...

Semiclassical

Hmm. In what sense 'bad'?

Emilio Pisanty

@Semiclassical why do people keep talking about how the $V=\pm x^4$ is self-adjoint or not without including the kinetic term like it isn't essential to the question?

0celoñe7

@EmilioPisanty Abuse of notation.

Semiclassical

I guess I'm taking it for granted in this discussion.

0celoñe7

00:22

I am including it, mentally.

Semiclassical

Ah.

0celoñe7

Not when I say $V\in L^p$, etc. of course.

Sir Cumference

@rob Sigh, there's no discrete way to share that then

Emilio Pisanty

@0celoñe7 well, that abuse of notation makes whatever people say with that abuse completely unintelligible

0celoñe7

@Semiclassical It's in none of the usual spaces analysts like to work with.

heather

00:23

@SirCumference email via your SE email?

Semiclassical

Does stuff that people say in chat but delete within five minutes stay in the system?

That's at least not public.

0celoñe7

@EmilioPisanty Well excuse me but in my message to you I wrote $H=p^2+x^4$, did I not?

rob

@Semiclassical No, deleted chat messages have a history that hangs around.

Emilio Pisanty

@0celoñe7 which is why what you say is understandable and what others say is not

Semiclassical

Gotcha. But they do have the advantage of not being public knowledge.

skullpatrol

00:25

Yeah, you can't google search a deleted message.

Semiclassical

I feel like I'm getting confused on this other business, though.

heather

@Semiclassical chat.stackexchange.com/messages/39073419/history

0celoñe7

@Semiclassical There are also results that require $V\in L^2+L^\infty +\{f\in L^2_\mathrm{loc}: f\ge 0\}$ that give essential adjointness for $H$.

Semiclassical

@heather huh

0celoñe7

People have written books about these questions

Semiclassical

00:27

Ah. So your point is that there's more than one way to achieve adjointness (not an iff).

ACuriousMind

The history of a deleted message, though, is once again only accessible to mods (looking at that is not logged, though)

0celoñe7

@Semiclassical Right, I am just giving some conditions I am aware of as examples

This is certainly not my field

Semiclassical

Right.

0celoñe7

I would like to know more mathematical QM, but lazyness

Semiclassical

Funnily enough, I actually do care about potentials like $V=aq^k$ right now, but not exactly in a quantum context

ACuriousMind

00:28

More in a...semiclassical context?

0celoñe7

@Semiclassical I will endeavor to read Lieb's "The Stability of Matter in QM," which proves that large quantities of quantum mechanical matter don't explode/implode.

Bernardo Meurer

@rob What the hell man

That's me

Semiclassical

@ACuriousMind rimshot

Bernardo Meurer

I'm the only Brazilian here

and the only one living (not anymore) in portugal

ACuriousMind

@BernardoMeurer that we know of

Bernardo Meurer

00:29

@rob How did you not know me

ACuriousMind

Need I remind you of:

Feb 18 at 14:55, by Bernardo Meurer

@ACuriousMind Why are you vandalising my city?

rob

@BernardoMeurer It's been a while. I'm bad with names. Your little squares are the same size. I'm a bad person. I prostrate myself before you. Et cetera, et cetera.

0celoñe7

@Semiclassical don't worry, I will write a thing on $p^2-x^4$ in a bit

Semiclassical

I'm interested in integrals of the form $\int_{-\infty}^\infty e^{-S(x)}\,dx$ where, for instance, $S(x)$ is some quartic in $x$.

and understanding how that behaves under analytic continuation of the coefficients of $S(x)$.

The simplest case being something like $S(x)=x^4+\mu x^2$.

skullpatrol

(removed)

0celoñe7

00:31

@Semiclassical That seems much more grounded than the usual mathematical physics we see in this chat :P

Semiclassical

lol

ACuriousMind

Hey! :P

Semiclassical

If QM is like a d=1 field theory, this is like a d=0 one.

Emilio Pisanty

@Semiclassical so, isn't all of that already done in some 1970s paper by Michael Berry?

Semiclassical

@EmilioPisanty Probably.

0celoñe7

00:32

@ACuriousMind You gave up your right to defend yourself when you said that 4 dimensions are not enough for you

4

Emilio Pisanty

it tends to do that with alarming frequency

Semiclassical

It's definitely in the realm of Borel stuff.

ACuriousMind

@Semiclassical Studying the physics of motion in no direction, then? ;)

Semiclassical

The paper which I need to sit down and read proper is one of Witten's, where he talks about this stuff (including some toy examples like the one here, thank goodness)

@ACuriousMind lol

0celoñe7

@Semiclassical Interesting. I am reading a Witten paper too...

There is a Witten paper for everything

Semiclassical

00:33

The reason I'm interested in it is because that potential has one minimum for $\mu>0$ but two for $\mu<0$.

ACuriousMind

@0celoñe7 the world is not enough!

@0celoñe7 Truer words have never been spoken

Semiclassical

What's really hilarious is that I actually saw this paper when it came out a few years ago, and read into it enough to remember this stuff.

0celoñe7

In math there is a Yau paper for everything

Semiclassical

But only realized "oh yeah I should go back and look at that again" when another paper referenced it

skullpatrol

Ok

0celoñe7

00:34

@skullpatrol Yau

Yau even did quantum mechanics for a while

ACuriousMind

...I was looking at a Strominger-Zaslow-Yau paper just yesterday

skullpatrol

Terrance Tao is good too.

0celoñe7

You mean Tao

ACuriousMind

Tao. Eastern philosophy, not Greek letter :P

rob

You mean Terrance 2π

skullpatrol

00:37

:-D

Bernardo Meurer

@rob You broke my heart man, not cool

@ACuriousMind Lol, that was funny

I remember seeing that and being like "Fuck"

Semiclassical

It's this paper, for reference: arxiv.org/abs/1001.2933

rob

@BernardoMeurer Words cannot express my sadness. I haven't been in chat for a while. Please forgive.

Semiclassical

though I don't care at all about the field theory in there :)

skullpatrol

and forget

0celoñe7

00:39

@Semiclassical This Lieb book is actually closely related to what we've been talking about. He examines the ground state energy for various Hamiltonians to prove they are stable.

Semiclassical

Ah, neat.

0celoñe7

@Semiclassical For instance, it follows from Sobolev inequalities that hydrogen atoms don't implode.

Semiclassical

lol

ACuriousMind

Praise be upon Sobolev, then

Never thought I'd say that

0celoñe7

@ACuriousMind There is hope for you yet!

rob

00:40

@BernardoMeurer Every single time I teach a class, I have two students whose names I mix up all semester, no matter how hard I try. One of my courses last year, the two students I kept mixing up were the only two black men in the class. They noticed and gave me an extra-hard time about it.

skullpatrol

:O

rob

Well, I got it straight eventually.

0celoñe7

@Semiclassical If you squint hard enough the energy expectation value $\int |\nabla \psi|^2+V|\psi|^2$ looks like a Sobolev norm...

Semiclassical

maybe if you know what a Sobolev norm is :)

skullpatrol

How many people were in the class?

@rob

rob

00:42

@skullpatrol Thirty.

0celoñe7

@Semiclassical $(\int |f|^2+|\nabla f|^2)^{1/2}$

Semiclassical

Ah, yeah.

skullpatrol

Ok, you're forgiven :P

rob

@skullpatrol How many were you imagining? Three?

skullpatrol

Strange how the brain works sometimes.

Nah, 10.

rob

00:45

@skullpatrol Yes, that'd be different.

skullpatrol

Was it a math class?

ACuriousMind

@rob Do you actually need the names? I'm pretty sure most TAs/profs here don't know half the names of the students in their class, unless the classes are really tiny.

rob

@skullpatrol Intro physics.

0celoñe7

I just cut myself on a plastic spoon

skullpatrol

-_-

rob

00:48

@ACuriousMind I think it's important to know my students' names, and I try hard at it. It certainly makes them more comfortable asking questions. This is also in a lab class, where we have conversations like "why is your experiment broken?" Names are an excellent lubricant.

0celoñe7

@ACuriousMind Most of my professors know most of the names

My thermo professor knew all 60 of us by name

skullpatrol

Impressive^

0celoñe7

Handler couldn't give less of a shit what our names were

And I think Spanier legitimately hated all of us, so he didn't know either

rob

@skullpatrol It's a skill. There are techniques. I do a little better every semester.

skullpatrol

Cool.

ACuriousMind

00:51

@rob I witnessed a conservation of that type: A friend of mine had to explain why the bob of the pendulum (which had a sharp metal end so you could read its location off a scale mounted behind it) was now firmly embedded into the table. Apparently "I wanted to see what happened when turned that screw" is not a valid answer.

0celoñe7

So you're looking for experiments which prove that the standard treatment of quantum mechanics is wrong? — Cort Ammon 34 mins ago

@ACuriousMind I think my answer to this was a little flip, but at the same time not.

Thoughts?

ACuriousMind

Got nothing on the TA who poured a dewar full of liquid nitrogen on a student's bag by accident, though

Semiclassical

Damn.

0celoñe7

@ACuriousMind what the hell

ACuriousMind

@0celoñe7 The same TA also ran out of the room two hours before lab time was over, yelling "Oh god, my train!"

It was a bit surreal

0celoñe7

00:54

#GermanyProblems

skullpatrol

Did you put a bandage on your cut?

0celoñe7

@skullpatrol cut the inside of my mouth

I was licking the spoon after putting leftovers in a box

skullpatrol

plastic spoon?

ACuriousMind

@0celoñe7 I think you might increase your chance of getting the answer you want if you explained in more detail/in an example what sort of sloppiness you mean because right now the commenters seem pretty confused about what you're actually talking about

0celoñe7

@ACuriousMind Do you know what I am talking about?

ACuriousMind

00:57

@0celoñe7 I think I do

0celoñe7

@ACuriousMind And I think that anyone who knows enough math to know what I am talking about will understand me.

skullpatrol

An example never hurts.

ACuriousMind

@0celoñe7 Well, but the point is that you need someone who actually has an overview over the experimental literature, and I think most people who know what you're talking about will, like me, don't have that overview. I mean, I already pointed out the domain issues thing with the HUP on a ring/in a box which I think should be in principle measurable, but I have no idea whether anyone ever did that.

So the better you explain the issue, the larger the chance someone with juuust the right amount of knowledge of both the math and the experiments might catch on

skullpatrol

A well thought out example will make the question much more "concrete."

0celoñe7

@ACuriousMind Yeah, that is a good answer. Did you see that in a class?

ACuriousMind

01:03

I think it's in Gieres' paper "mathematical surprises in Dirac's formalism", which was indeed recommended to us by our QM lecturer

This one

0celoñe7

@TheDarkSide See page 5 of ^

Figure 2.1

@ACuriousMind I know it

skullpatrol

Why not put the link in the question?

0celoñe7

@skullpatrol Calm down, I am thinking

skullpatrol

yes sir

0celoñe7

@ACuriousMind In the last displayed eq. in that answer, do you really mean $D(A)\cap D(B)$?

That commutator doesn't really make sense on that space. The last equality does, but how did you jump without using $\psi\in D(AB)\cap D(BA)$?

ACuriousMind

01:09

@0celoñe7 Ah, I don't mean the commutator makes sense - just the r.h.s. and the l.h.s. I'd have to think about how one gets that inequality not using the commutator, but I'd rather not do that at 3 am ;)

0celoñe7

@ACuriousMind Apparently the actual derivation of the HUP goes from your last equation to the commutator.

ACuriousMind

I would suspect that, yeah

Yes, it does

0celoñe7

@ACuriousMind Maybe you knew this, but on $\Bbb R$ one can show that the HUP holds in $D(X)\cap D(P)$, one doesn't have to worry about products.

0celoñe7

01:35

@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

heh, I figured it'd be something to do with the boundary term in integration by parts

0celoñe7

@Semiclassical There's a less computational abstract nonsense proof

Semiclassical

What's $H^*$ supposed to be?

0celoñe7

@Semiclassical The adjoint of $H$, defined in a message to you above.

Semiclassical

ah.

0celoñe7

01:42

@Semiclassical In the abstract proof, one shows that $H^*$ has an "almost eigenvector" with an imaginary eigenvalue.

Which of course cannot happen for symmetric operators.

Semiclassical

Hmm.

That sounds right, if only because the potential would be classically unstable, and so one would expect particles to have a finite lifetime

Which is exactly what an imaginary part of an energy eigenvalue would correspond to.

0celoñe7

How so?

Semiclassical

If $H^*\psi =i\lambda \psi$, then $e^{i H^* t}\psi = e^{-\lambda t}\psi$.

Which would amount to the particle being less and less likely to be found anywhere. Thus, finite lifetime.

I would think this becomes further interesting if $V=-x^4+ax^2$ with $a>0$, since then there's a local minimum at zero. Hence one does have a metastable state.

(If the particle was classical, then it'd remain at the origin if it starts there and there's only a small perturbation. But quantum mechanically it can always tunnel past the barrier and escape to infinity.)

0celoñe7

right

interesting

Semiclassical

The case of $V=x^3-ax$ is interesting for similar reasons: when $a>0$, there's a local minimum. but it's still unbounded below

0celoñe7

02:01

@Semiclassical Also interesting in this Lieb book is that they estimate $\alpha$ based on the anthropic principle

stability holds only for $\alpha$ small enough, stuff like that

Secret

02:25

Interesting how particle lifetimes can be thought in terms of how likely it tunnels forever down to somewhere that is unbounded below

But is it physically possible to have an unbounded below position in a potential surface without the diverging amount of energy that is expected to release as the particle roll downhill indefinitely?

Secret

02:41

[Unrelated worldbuilding] A potential energy well with a torus like topology, such that falling far enough will loop back to the top. Thus particles can fall forever in this state. It is possible, however that such perpetual motion system has to have its entropy maximised somehow to prevent any further release of energy in the process, otherwise it will introduce divergence

Downcycling

Downcycling, also referred to as cascading, describes the recycling of waste in cases where the recycled material is of lower quality and functionality than the original material. An important example of downcycling is the accumulation of tramp elements in secondary metals, which may exclude the latter from high-quality applications. Steel scrap from end-of-life vehicles, for example, is often contaminated with copper from wires and tin from coating. This contaminated scrap yields a secondary steel that does not meet the specifications for automotive steel and therefore, it is mostly applied in...

Upcycling

Upcycling, also known as creative reuse, is the process of transforming by-products, waste materials, useless, or unwanted products into new materials or products of better quality or for better environmental value. Upcycling is the opposite of downcycling, which is the other half of the recycling process. Downcycling involves converting materials and products into new materials of lesser quality. Most recycling involves converting or extracting useful materials from a product and creating a different product or material. == Background == The first recorded use of the term upcycling was by Reiner...

Circular economy

A circular economy is a regenerative system in which resource input and waste, emission, and energy leakage are minimised by slowing, closing, and narrowing material and energy loops. This can be achieved through long-lasting design, maintenance, repair, reuse, remanufacturing, refurbishing, and recycling. This is contrast to a linear economy which is a 'take, make, dispose' model of production. == Scope == The term encompasses more than the production and consumption of goods and services, including a shift from fossil fuels to the use of renewable energy, and the role of diversity as a ...

More philosophically, it does make me wonder, do the concept of loops special compared to other concepts

for it is really the only known concept known to our species that can make infinity bounded without diminishing its magnitude

Secret

03:05

in Mathematics, 1 min ago, by Secret

What else, besides cycles and convergences, can tame infinity?

to me, (analytic) philosophy allows you to play with concepts as if they are particles and ask what happens when you brought them to interact

bu then, there's this danger of the map/territory fallacy and then you lost track of reality

0celoñe7

@BernardoMeurer ahahah get rekt

Bernardo Meurer

@0celoñe7 What was funny

0celoñe7

michelle

@BernardoMeurer I need to learn C

Bernardo Meurer

@0celoñe7 I can teach you :P

The Raiders of Las Vegas

ABC you're done.

Bernardo Meurer

03:20

@TheRaidersofLasVegas More like ABC SIGSEGV

0celoñe7

@BernardoMeurer latest h3 video is nsfl

Secret

printf ("Hello world");
for i = 1, i < k, i+=5
{
printf ("Countup: i");
}
printf("Bye world");

Bernardo Meurer

@Secret That's not valid syntax

at all

Secret

must have missed/added a bracket or ; somewhere...

Back in my high school, my most common syntax error is missing out ; somewhere

But it has been years since I last touched C, so...

0celoñe7

@SevenSidedDie Ah, apparently there is a way to partially hide a mesh -- useful when you want to reduce clipping from things that don't actually need to be shown.

dmckee

03:29

@SirCumference I'd like to echo what @EmilioPisanty said. A lot of people get into grad school without doing the hard thinking first. It makes a lot of us jump in to explain the (non trivial) downsides first.

0celoñe7

@dmckee

dmckee

There are some real upsides in terms of self-actualization and the pure pleasure of digging into a subject you enjoy at great depth, and most people who make it through grad school describe it as being a time of great enjoyment as well as a time of great stress.

@0celoñe7 Gotta love VSTOL aircraft, don't 'ya?

@SirCumference You've been doing the hard thinking, so I wouldn't want to only tell you the bad parts.

0celoñe7

@dmckee Not a VSTOL en.wikipedia.org/wiki/Airbus_A400M_Atlas

it's a big damn plane

dmckee

Grad school will make you cry on the bad days, but it will also take you to some dizzying heights on the better ones.

Bernardo Meurer

@Secret Missing parenthesis on for arguments, missing declaration of i, argument separator is ;, missing appropriate string formatting for i (right now it prints the character i, not the variable), missing main function, missing stdio header

I think that's all

dmckee

03:35

@0celoñe7 VSTOL is "very-short take off and landing" it applies to a crafts capabilities. That qualifies on the take-off part at least.

0celoñe7

@dmckee I know what VSTOL is, and that plane is not explicitly labeled as such

I thought VSTOL was carrier-capable

Bernardo Meurer

#include <stdio.h>

int main (){
printf ("Hello world\n");
int i = 1;
int k = 100
for(int i = 1; i < k; i+=5) {
    printf ("Countup: %d\n", i);
}
printf("Bye world\n");
}

Now it's right I think @Secret

Secret

yeah. looks good to me

(forgot whether there is a %i for integers though, but double is also fine)

Bernardo Meurer

%d is for decimal

%lf is for double IIRC

actually just %f works for float and double, right @dmckee?

Dawood ibn Kareem

%d is for ints. I'm fairly sure that whether %f works for float and double is actually platform dependent.

But I may be wrong because I haven't programmed in C for a very long time.

Bernardo Meurer

03:54

@DawoodibnKareem %d is for ints, yeah

I meant that I think they chose "d" because of "decimal"

@DawoodibnKareem On most system both Float and Double implement IEEE754

With single and double precision respectively

Long double with quadruple precision, but still with IEEE754

IEEE 754

The IEEE Standard for Floating-Point Arithmetic (IEEE 754) is a technical standard for floating-point computation established in 1985 by the Institute of Electrical and Electronics Engineers (IEEE). The standard addressed many problems found in the diverse floating point implementations that made them difficult to use reliably and portably. Many hardware floating point units now use the IEEE 754 standard. The standard defines: arithmetic formats: sets of binary and decimal floating-point data, which consist of finite numbers (including signed zeros and subnormal numbers), infinities, and special...

I've had problems with this before

Trying to make an FPU in an FPGA

dmckee

05:16

@BernardoMeurer Well, ... you can pass a float, but it get promoted to a double as part of the default behavior of variable arguments.

So the %f specification formats doubles.

John Rennie

@dmckee ah, I had never realised that. I guess it makes sense to try and impose some order on variable arguments.

I've never been sure whether the variable arguments are an amazingly useful feature that every language should have or a disastrous hack responsible for a near uncountable number of kernel dumps. Possibly both :-)

0celoñe7

To coffee or not to coffee

The Raiders of Las Vegas

That is the question

Loong

That is no question here.

The Raiders of Las Vegas

To coffee or not to coffee, that is the question.

Loong

05:31

Heh, I could get a week of main control room simulator training.

I don't really need it, but why not.

The Raiders of Las Vegas

paid training?

John Rennie

I might have another coffee ...
Some mornings just seem to be slow starters.

Loong

@TheRaidersofLasVegas Yes, I am paid for my job. :-) And if management decides to send me to our simulator during my work time, I probably don't say no.

The Raiders of Las Vegas

Go for it (The training, I mean).

0celoñe7

Skyrim is finally playable

The Raiders of Las Vegas

05:37

Nothing like getting paid to learn @Loong :-)

Loong

:-)

0celoñe7

oh no

I need to do laundry

it's 1:40 AM though

I need a butler

The Raiders of Las Vegas

Nobody does laundry at 1:40 A.M.

0celoñe7

except for me apparently

The Raiders of Las Vegas

Can't you live with dirty clothes for a day?

Joshua Lin

05:46

? i do laundry at like 1 or 2 sometimes too

The Raiders of Las Vegas

Ok ok. I stand corrected.

0celoñe7

@TheRaidersofLasVegas they are clean and half folded on my bed

have to finish putting them away

The Raiders of Las Vegas

icic

djsmiley2k

06:14

Laundry at 1am means it's finished by like... 9am

which if you start work late, is ideal.

The Raiders of Las Vegas

Sounds like a graveyard shift of laundry.

DanielSank

@djsmiley2k 8hr laundry?

djsmiley2k

well the washing machine takes like 4 hours

Rumplestillskin

07:01

Does anyone know the significance of the following situation: you calculate the Einstein tensor in spherical coordinates and the components $G^{22} = G^{33}$?

John Rennie

@Rumplestillskin The Einstein tensor $G$ as in $G = 8\pi T$ ?

Rumplestillskin

Yep, the Einstein tensor. I think it's to do with spherical symmetry is that correct?

@JohnRennie

John Rennie

The Einstein tensor is proportional to the stress energy tensor, so it just means $T_{22} = T_{33}$. That may or may not be interesting depending on your system.

Rumplestillskin

07:16

Nah, it arose studying an exterior vacuum solution. @JohnRennie

Dawood ibn Kareem

07:59

@dmckee Yes, I stand corrected. %f will work for either float or double, because of the promotion rules, but you need %Lf for long doubles. Also, %d and %i seem to be synonymous. @BernardoMeurer

In my defence, the last time I wrote a C program was in 2000.

Slereah

@Rumplestillskin Because of the spherical symmetry

you can probably prove it by Killing vectors

Slereah

08:14

the wiki article on Misner space is still shit

Let's edit it

Slereah

09:07

Misner space

Misner space is an abstract mathematical spacetime, discovered by Charles Misner of the University of Maryland. It is also known as the Lorentzian orbifold R 1 , 1 / boost {\displaystyle \mathbb {R} ^{1,1}/{\text{boost}}} . == Metric == The simplest description of Misner space is to consider two-dimensional Minkowski space with the metric d s ...

Bare minimum to make it less terrible

The old article didn't even have the metric

user228700

09:45

@JohnR: Yello! :-)

John Rennie

Morning. In Kerala now?

user228700

Yep. I've left Chennai :'-(

John Rennie

Don't be down. You'll be back in ... 6 weeks was it?

user228700

Yep, yep.

user228700

However much I have learned to despise Kerala though, I gotta admit that it's fracking beautiful:

John Rennie

09:49

Greener than Chennai anyway :-)

Are you at your gran's house?

user228700

John Rennie

That does look nice

Bought the mattress?

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