The h Bar

Or just rename gmon.out gmon.exe to make the existing file work.

Anonymous

Anonymous

It seems changing extension makes it a 16-bit app. My windows is 32-bit

Anonymous

I made a mistake while typing over there

@BernardoMeurer Sure. I worked it in c, too. But you don't have to work the whole thing to get the main message which is 'a compiler is just another program' so that all the theory is a "real" compiler book has a purpose.

Anonymous

5:06 PM

"then"

@blue is this for your course?

@Blue and does the course assume you're using Linux?

@blue not:

gcc gmon.c -o gmon.exe then gmon.exe <in.txt >out.txt

I meant:

gcc gmon.c -o gmon.exe
gmon.exe <in.txt >out.txt

Anonymous

@JohnRennie Actually, yes. But we have only the theory of file handling. We aren't expected to run it in on pc. I was trying it out so that I can learn the usage of cmd

Hang on, where is the C file?

gmon.c or whatever it is?

Anonymous

@JohnRennie On desktop

Anonymous

It's gmon.out

Anonymous

5:13 PM

The .c file is abc.c

Anonymous

Which you can see in the picture

Ah, OK, use:

gcc abc.c -o gmon.exe

to compile the source and produce the executable gmon.exe. Then:

gmon.exe <in.txt >out.txt

to run it.

(assuming you want to call it gmon.exe)

@0celo7 out of curiosity, why do you need to learn K theory?

The -o flag to gcc tells it what to call the object file.

@Blue I asked about unix because Windows 10 has a unix subsystem built in. This works just like proper unix with all the same file name conventions etc.

If your course uses unix this might be easier than coping with the differences between Windows and unix.

@JohnRennie huh, really

that's neat

5:21 PM

@Semiclassical yes, it's full Ubuntu Linux. You just need to enable it as it isn't enabled by default.

kk

Anonymous

@JohnRennie Awesome. It works now!! BTW could you explain why this time it isn't complaining about exe being 16-bit this time?

I think your .exe file had got mangled somewhere in amongst all the garbled commands.

Anonymous

@JohnRennie We normally use Windows in the lab. And, our textbook doesn't mention any OS in particular. It is just a generic C textbook

OK, I guess using the Linux subsystem is a bit pointless then.

5:24 PM

So apparently I got 6 upvotes for this... ummmm... uhh... hmm.

Anonymous

@JohnRennie Yeah, I don't know why my book used Linux syntax (/).

Anonymous

Several people have been telling me to switch to Linux for this reason though

Fawad

Anonymous

Like, some things are much easier to do with Linux

Anonymous

compared to Windows

Anonymous

5:26 PM

I don't know the exact differences between them

Anonymous

Never used Linux

Well, like I say, if you need Linux it is built into Windows. You don't need a separate computer or to reinstall your existing computer.

But if you're used to Windows you'll find Linux a steep learning curve

I think I've had a dumb idea but I feel like there's a chance it's not. For rank nullity, given a linear map $A$, such that $A:V \to W$, if I define an equivalence relation E, such that for $q, p \in V$, $qEp$ iff $A(q) = A(p)$, then take the quotient space of V with E, $V/E$ and then just use the fact that for a quotient space between R^n / R^m, the dimension of resulting space is $n-m$, or that it's bijective to $R^{n-m}$. So then it follows that $dim(V) = dim(V/E) + dim(E)$?

Anonymous

@JohnRennie Oh, can I just download that online? (Without having to get rid of existing Windows?)

Anonymous

@JohnRennie I can try :P

5:28 PM

@Blue Yes. Shall I talk you through it now?

Anonymous

@JohnRennie Well, got an exam tomorrow morning. Maybe over this weekend (if you will be free)? :)

Fawad

@Blue yes I'll be here as usual

Anonymous

@JohnRennie Great. Thanks!

@0celo7 halp

5:34 PM

@Blue C was originally developed in parallel with unix and the bible (Kernigan and Ritchie) was written assuming you were working from a unix command line. Many books since have followed suit.

@Blue I've cancelled the star on the post you wanted removed from the star board

If you want to do K&R style exercises on a lot of other platforms you need some kind of compatibility hack (conio.h, anyone?).

But I've helped people learn on unix, dos, mac system 6, and a windows from the 90s, so there is no huge barrier to learning on non-unix platforms.

Anonymous

@dmckee I see. Didn't know that!

Anonymous

@JohnRennie Thanks

Anonymous

I'm using the Schaum series book by Gottfried

5:43 PM

@Phase what

@0celo7 The question above

about quotient spaces

btw dim(E) was meant to be dim(classes) but hit character limit

@Blue you could also inquire at cseducation.se

Anonymous

Inquire what?

Anonymous

"Beta Q&A site for those involved in the field of teaching Computer Science"

Anonymous

Phew...how many more CS sites do they want...

Bret Victor The Future of Programming

5:47 PM

►

@Phase sorry I’m off duty today

@0celo7 ok math cop

It’s thanksgiving

oh yeah I forgot that exists

Is that just a celebration where people eat Turkey?

and give thanks

5:54 PM

@Phase Turkey the country?

@JohnRennie I know right its so inhumane

You're mixing it up with tanks-giving

That's when thousands of tanks roll across the border :-)

I thought that's celebrated in Ukraine?

And the Crimea of course

Not that the US haven't done their fair share of driving their tanks into other peoples countries ...

Anyway

Since it's the festive season

I mean the surface area of my plate is $\approx 3.14\times 10^{-8}$km$^2$ and there's $\approx$ 320 million americans and turkeys surface area is 783000km$^2$. So to eat Turkey in thanksgiving each American would have to eat $\approx$ 78000 platefuls...

Not too many

5:59 PM

I present to you todays healthy and fat free meal

Brussel sprout risotto!

ewwwww ;p

Someone had to stop Rommel :-)

Oh John have you seen Sainsburys christmas advert this year?

It was nice. I like sprouts.

Can't say that they're my fave.

6:01 PM

@CooperCape yes, I watched it on their web site. It seemed uncontroversial, if rather dull ...

My friend works there and he hates it so naturally I've learnt it and now constantly sing it to him.

@skullpatrol that was us Brits ...

Just interested in a 3rd party opinion ;p

Right, Montgomery.

@CooperCape Meh. It's just an advert.

6:03 PM

faiiir.

John Lewis one this year is... odd.

i miss the pepsi ad

"join the conversation" "drink pepsi"

@CooperCape I don't have a TV so I don't see adverts

What happened with your academic review? @Phase

They decided not to kick me

To my surprise a lecturer I thought hated me vouched for me

cool :-)

6:09 PM

idd :)

that's encouraging

Oh my God!

That's ... that's ... oh, who gives a toss anyway :-)

@JohnRennie at least we can still play Euro Truck Simulator

@Phase it crashes out? :-)

The only thing crashing out is my life out of snooze-ville

all aboard to woke-opolis

6:18 PM

time to show them what you can do when you try hard

@Phase did you get your question answered

Yeah

He said "prolly right"

@JohnRennie I wanna post a funny thanksgiving meme but Idk if it'll get flagged

@JohnRennie Ahh okay... Tbh I don't watch a lot of tv anyways I just get them as youtube adverts ;p

Play it safe and don't @Phase :-)

b...

:(

6:30 PM

You could link it under not safe for haters of something...

if it's on imgur

I'll post a gyazo link

so it doesn't appear as a picture

just some experienced advice pal

gyazo.com/e388f387a3f0f8c63498eb001031ff5e dont click if sensitive

inb4 chatbanned

that's weird

like... weeeeiiird.

6:33 PM

ikr

bolbteppa

@Phase congrats, keep in touch with your tutor and use doctors notes if sleep issues start up again to pre-empt future issues

@bolbteppa still havent even had my appointment with the counsellor yet : P its in a week or so iirc

ty for the congrats and consideration tho

Indeed, best of luck.

bolbteppa

Cool, let your tutor know you have set up an appointment, keep your tutor updated on this stuff (that's what they are there for), I know it sounds lame but who cares about lameness compared to getting kicked out over this s**t

I'll be fine, I've had 100% attendance the past 3 weeks

@bolbteppa he actually had to refer me in the end : P i spent like a week and a half waiting for a response, when he referred me it was instant

bolbteppa

6:36 PM

Good stuff

Are you still going to switch to maths?

Next year, :/\

Im just gonna focus on the day in day out this year

and try to get a good enough grade in everything that everything goes smooth from there

Btw in my mechanics lecture Im pretty sure my lecturer and a question was wrong

Anonymous

@Phase What question?

It went like this "You're in an elevator that's broken, and is falling down in freefall, if you jump does it give you a better chance to survive"

But you cant jump in a falling elevator, it's identical to freefall so you'd just pull your feet off the floor and curl up in the air

relative to the lift

right?

Anonymous

@Phase Umm, no. Think of Newton's third law

6:40 PM

My point is you can't crouch to do the jump

Because you'd be lifting your feet off the floor, rather than lowering your body to the ground

Everything falls at the same rate, right?

what if you pre-crouched...

yup

@CooperCape who walks around precrouched : P

People who are scared of lifts? Idk...

Tbf I kinda hate lifts

Lifts are great

Lifts are less scary than walking 16 flights of stairs because you wanted to buy a sandwich

@Blue do you get what I mean now?

6:42 PM

Yeah true I haven't reached the uni 'this building is very tall' level of tall buildings yet

Nah it was my student accomodation last year

was on 8th floor

that'... tall.

Anonymous

@Phase I think by jumping they just meant pushing on the floor of the elevator using your feet, so that it exerts a reverse force on you

Yeah but you couldn't lower yourself to do the jump

If you were stood straight as it broke free you would be unable to jump

Why can't you bend your knees?

6:45 PM

You can, but your feet will come off the floor of the lift

Anyways surely if you jump it's still freefall you'd just... kinda... increase the height... right?

You'd always decrease your velocity relative to the ground a bit

If you can jump, it's good, but I just dont think you can

Provided you werent crab walking into the lift

Anonymous

I can suggest a crude way of doing it. Use friction of the walls to move as close as possible to the floor (using your hands). When you are sufficiently close to the floor and crouched, then straighten your legs, exerting as much force as possible on the elevator floor. That will reduce your momentum and increase the elevator's momentum

Anonymous

Obviously in such a short span of time, such a thing is impractical

Idd, but my lecturer wasn't convinced by my argument that you wouldnt be able to crouch to the floor

:/

6:49 PM

What is mechanics like in a phys degree cause ngl I kinda dislike it at A level (severely)

It's crap until you do it in terms of energy @CooperCape

Anonymous

You can crouch. But it's gonna be complicated :P

Brilliant

You can't crouch, not really : p you're relying on conditions that aren't stipulated

I.e. there being walls close enough to you that you can use

It's just all this forces n' stuff is really dull... Like idc bout ladders n stuff.

By forces I mean like on a rod...

against a wall

Anonymous

6:50 PM

Even in zero gravity you can throw your clothes off, so that you are pushed towards the wall. :P

yay.

@Blue but the momentum change will be quite minor indeed

Anonymous

@CooperCape Uni mechanics is very very very different

Anonymous

@Phase That's true.

@CooperCape imo it gets fun when you consider Hamiltonians and lagrangians

and before then its boring

6:51 PM

Oh really? I kinda figured (hoped ;p)

Uh huh

Anonymous

It doesn't get easier though :P

you've already encountered hamiltonians in a way

Since you've undoubtedly used $\frac{dT}{dt} = -\frac{dV}{dt}$

Ehhh it's not too bad currently... except for ummmmmm something I struggled with

Oh yeah pulleys cause I fell asleep in class and never got round to learning them...

But if they frictionless I figure you can probs ignore them really

I doubt know what T or V is in that but... possibly.

Anonymous

@CooperCape Try the Irodov problems if you want some brain melting problems in high school mechanics

Uhhhh maybe I'm fine? ;p I'll see if I have a spare moment...

6:54 PM

T is kinetic and V is potential

Like when you consider something going down a ramp

Ignoring friction / drag, the potential energy is converted into kinetic energy

Uh huh...

Yeah...

That comes from considering the total energy to be a constant, H

H = T + V, and then differentiating it

I see... so basically it's what we meagre A level students casually take for granted? :p

Nah, my example is really trivial

Anonymous

But I really don't like using energy method while solving real mechanics problems. Force method always provides you better intuition

6:55 PM

In reality you use funky equations

@Blue but forces are horrid

oooh funky.

Won't lie I'm more of an energy guy on my basic boi problems...

Anonymous

@Phase It's more masochistic

Anonymous

Once you are successful in solving by force method, you'll really understand what you've been doing

Yeah I mean

I love finding the eq of a double pendulum with forces :)

: P

if the elevator is accelerating upward, are you able to jump up off the floor then? @Phase

7:03 PM

Absolutely

Just with great effort

The problem with jumping in an elevator in freefall is that you no longer maintain contact with the surface if make a crouching motion

@Semiclassical o_O remember our Dewitt dialog? enjoyed it, thx for the lead(s)! care to continue? just googled up a storm of eyepopping hydrodynamics/ fluid dynamics connected to QM refs wrt research program with ~1 member, intend to write em up in blog eventually but wanna share em with someone who wont immediately scoff at them (which effectively disqualifies quite a few high/low-rep users around here!), youre the nearest in all of cyberspace at moment, whaddya say :| :) :P

not at the moment. between having just eaten thanksgiving turkey and needing to type up some of my own stuff, I'm a bit preoccupied :)

Sid

@skullpatrol imagine if the acceleration is greater than "g". We don't even have to make the effort to jump. :P

Anonymous

@vzn's style of writing with minimal usage of "I" and "me" is really something unique. Also the slashes!. :P

@Semiclassical lol thats what one gets for asking for permission instead of begging for forgiveness ... have to go to long/ boring family thxgiving mtg myself shortly was hoping for some cyber chat to rescue me :|

7:08 PM

yes, it gets me telling you that I'm not interested instead of me just ignoring you :P

@Blue am so remarkable that others can now refer to me in 3rd person? beams

Yeah @Sid this is a classic question :-)

← truly utterly unique... just like everyone else! :P

Anonymous

@vzn hehe :D

@Blue iirc tried to get you into alternative QM stuff once based on your own questions but it was nobody home :|

7:10 PM

just had thanksgiving lunch, and while it wasn't a long affair I'm definitely in food-coma mode

They don't call it "stuffing" for nothing :P

lol

stuff the bird, then stuff yourselves

tryptofan, natures own drug

The Men Collecting Stardust From Gutters and Rooftops / dailybeast

↑ for the cosmology fans/ geeks/ hobbyists/ DIYers :)

7:40 PM

Anybody good at numerical stuff? My code is totally unstable lol

How's the baby's first thanksgiving? @dmckee :-)

Q: Cannot find a question upon statistical mechanics I commented on

@JamalS just use std code. btw from your profile you are interested in solitons? :) btw have you heard of this, any interest? :) physics.meta.stackexchange.com/questions/7783/…

Physics Meta

0

perhaps you can help me track down a question I commented on (cannot find my comments in my list). It was about the Heisenberg and Schrödinger pictures of classical mechanics. I remember telling the OP about the book by Balescu and promised him to find other sources. I was now going to post an a...

support

@vzn I can't, it's for a class.

@JamalS what is the problem? most scientific problems have std solns.

7:48 PM

@vzn I'm solving $\partial_t v = \partial_{xx}v + v(\alpha-v)(1-v) - u$, $\partial_t u = \beta v$.

@JamalS What sort of numerics?

@ACuriousMind Coupled, non-linear PDE

@JamalS so its a PDE. use a std PDE solver.

Also, can I ask the panel to rate the truth of the following statement as a sanity check:

> Each type of energy is associated with a certain amount of entropy. For example, the mechanical energy, electricity, and laser light have low entropy. Other types of energy are not "entropy free", especially the heat energy.

@JamalS ew ;P

@vzn So your attitude is if you don't know something to find someone else's solution? Re-using code is fine, don't re-invent the wheel after all. But you need to know why it works then, and know why yours doesn't.

7:50 PM

@vzn The point of most numerical physics courses is not to actually solve the equation but to learn the numerical tricks required to solve it, so even if a "PDE solver" exists that can solve this particular equation it would completely defeat the point of these assignments to use it.

@JamalS lol, its called “science + software engr”

@vzn That does not remotely address my argument, and thanks @ACuriousMind

@vzn Have you heard of something called curiosity? Even if this wasn't an assignment...

@ACuriousMind pt taken but learning how std PDE solvers work is still learning. think thats more than ½ of numerical methods.

It's erm, the driving force behind research :P

@vzn Yes, but you can't learn how a PDE solver works by using it

7:52 PM

@JamalS what school are you at? undergrad? impressive profile

Yeah but I'm not going to read a massive codebase to solve a single PDE.

@JamalS obviously you dont have to.

My hands are tied using C, so I've just done explicit finite differences. If I was doing C++, I'd have implemented FAS multigrid on an implicit method.

@ACuriousMind it hasnt been established yet what course hes taking.

@JamalS ok, what field of physics is the eqn from? how do you know its “unstable” in your solver? etc

@vzn It's to model neurons, it's the Fitzhugh-Nagumo equations. I looked at results online and explicit finite diff isn't ideal but it supposedly works.

I believe mine is unstable as after 6 timesteps the values all go to nan lol

7:55 PM

ok, reasonable evidence. seems likely an incorrect implementation if you ask me

I have 10 years of C++ experience, so maybe the flaw is in the method, but definitely not the implementation.

are any of the constants “large”? dont see how it could diverge so “quickly” otherwise

No, all of order 1.

It's very bizarre.

just output intermediate values & try to diagnose it

@vzn Can I take you through how I handled the boundary conditions? Maybe I'm faulty there.

7:57 PM

@JamalS Does that happen regardless of which boundary conditions you choose?

@ACuriousMind I've used the ones given to me by the problem, which are suppose to not cause any problems. I've played with values.

@ACuriousMind Do you think the kerning on connected sum in standard TeX is too narrow?

Anonymous

@ACuriousMind I think that does make some sense. They're referring to entropy as a measure of energy dispersal. Indeed laser light has lower entropy than non-coherent monochromatic light. Low temperature diffuse heat has high entropy while electricity has low entropy. I'm not totally sure about the mechanical energy part. Need to check that.

Entropy (energy dispersal)

@Blue What does "electricity has low entropy" mean? Entropy is a property of a statistical system, not of "energy".

I mean, these phrases sound like they mean something potentially correct to me, but I can't quite see how anything in the actual formalism supports that.

@0celo7 I have no opinion on that

Anonymous

@ACuriousMind Actually, there's a different notion of entropy that exists too:

Anonymous

8:01 PM

In physics education, the concept of entropy is traditionally introduced as a quantitative measure of disorder. While acknowledging this approach is technically sound, some educators argue entropy and related thermodynamic concepts are easier to understand if entropy is described as a measure of energy dispersal instead. In this alternative approach, entropy is a measure of energy dispersal or distribution at a specific temperature. Changes in entropy can be quantitatively related to the distribution or the spreading out of the energy of a thermodynamic system, divided by its temperature. The energy...

@vzn The smaller I make my step size dt, the sooner it becomes unstable...

@Blue Gotta say that this isn't wrong but it has always struck me as a crippled, fuzzy-word-pictures attempt to do a proper statistical description without math.

@Blue You do see the giant disclaimer on that article, yes? :D

Also, I really think this is formally nonsense: Entropy is a function of state of a statistical system, but systems have energy even in non-statistical mechanics.

Just here . . . . reading over again defs of sphere in anal

Anonymous

@ACuriousMind I did. :P That's why I mentioned : "a different notion". You can find low entropy electricity mentioned in several electrical engineering papers

8:05 PM

going over some topology in anal

Heck, you can even do statistical mechanics where a macrostate is not necessarily fixed-energy (e.g. grand canonical ensemble), but of course fixed-entropy rather by definition

Anonymous

Even in some books they mention that electricity has lower entropy than diffuse heat

Anonymous

Like this

Anonymous

I guess mostly engineers would use such a notion

@Blue I've now read the article and I have no idea what the precise notion of entropy is supposed to be here

The article complains about "disorder" being vague and then proceeds to wave its hands around saying something about energy dispersal without ever really giving a definition of entropy.

8:08 PM

where's "rigour" when you need him :P

Anonymous

It's not really a well established term. Anyway, it's used by engineers. I doubt any good physics book would use entropy in such a way. It IS hand-wavy, and most of the articles I read on it are hand-wavy too.

Anonymous

As dmckee says:"crippled, fuzzy-word-pictures attempt to do a proper statistical description without math."

ok spheres, balls, simplices . . .

is that a picture of Las Vegas in your avatar? @Cows

hehehe yes

@sku

@skullpatrol yes, how did you know?

8:12 PM

Been there.

@skullpatrol nice. yeah it was some time ago, hehe

My team is planning to move there.

@skullpatrol team?

Raiders.

@skullpatrol oh nice

8:14 PM

Were you there during the shooting?

No I wasn't . It was quite a sad day. I live in California though

Yeah, I don't plan on going there to watch any games.

(for that reason)

well, . . there is danger everywhere, you have to be able to find a way to keep living

True dat.

Yeah I want to master real analysis. I want to be able to write physics with rigor. So every so often I open up an analysis text or surf the web for such

I wanted to start blogging (keeping a journal of sorts) of mathy and physics things I do in my spare time, but I have not found fiscal incentives for this yet hehe

@skullpatrol I take it you study math, or are a math prof?

Well I have a few , but the one I feel comfortable saying i read is the one by rosenlicht hehehe

8:23 PM

cool

I have looked at a few others recommended by users of this site, but eh lol

do you have a math blog?

nope

yeah, blogging takes quite a bit of time, and effort. Writing and Latex-ing is hard

yup, time better spent...

So, you a math student?

prof may be?

oh, that's cool lolz, was just curious hehe

yeah anonymity is pretty cool. Sometimes it enables one to navigate the internet without additional weights

So Happy Thanksgiving by the way

8:29 PM

Thanks, same to you pal :-)

:D

I bet Turkeys aren't excited though hehe

hehe

Anonymous

@Cows Why would you expect random people in the physics chat to be math profs rather than physics profs? :P

Anonymous

I mean you shouldn't even expect any profs here

Anonymous

They are usually too busy to chat (unless retired)

8:33 PM

We've known each other for awhile.

@Blue I dunno, I just spur the moment typed the question. Was not thinking too much about it hehe

hehe

Anyway, best of luck in your studies @Cows cya

@skullpatrol ok nice chatting

Mithrandir24601

@Blue dmckee's a lecturer I think

Anonymous

@Mithrandir24601 Yeah, but he rarely chats ;)

Mithrandir24601

8:40 PM

@Blue I guess so?

@Blue Well, he also has a tiny human to take care of!

@Semiclassical my advisor has told me how envisions my career going and some K theory is in there

And I agree

"I see K theory in your future" - worst fortune-teller ever ;P

Anonymous

@ACuriousMind Well, hehe :D Tbh, not only professors, but even most professionals have their work life and their family life. So they're almost always preoccupied.

Anonymous

People who want free time, shouldn't get married :P

user685252

8:46 PM

?

@Blue You may have a weird idea of marriage, then :P

Anonymous

Dunno, lol. I want to be like JR: hack computers, do physics and eat delicious food day and night.

Mithrandir24601

@Blue Well, I read books, do physics and eat delicious food day and night, so it's not too hard to do something similar :)

@Mithrandir24601 there is a difference. You get paid to do so

Anonymous

@Mithrandir24601 You're still young. I was talking about a bit older people, who have crossed the average marriage age

8:55 PM

Money is the most important thing on the planet. Trust me

2

It can make or break you

user685252

Not everything that counts can be counted.