The h Bar

Bernardo Meurer

00:04

@DavidZ :

0

First of all, I know triple and quadruple pointers are bad practice and are ugly, that's not the point of this question, I'm trying to understand how they work. I'm aware using a struct would be much better. I am trying to write a function that does some memory operations using memmove() and mem...

David Z

OK so there is definitely a null pointer being passed in there somewhere

Running memcpy(0x21c51e0, 0x21c5040, 20)
Running memcpy(0x21c51b0, 0x21c5060, 20)
Running memcpy((nil), 0x21c5080, 20)

Bernardo Meurer

@DavidZ Yep, Valgrind only screams about the memcpy, memmove seems fine

0celouvsky

@Slereah what's a good reference for things like $\hat\sigma_\mu \sigma_\alpha\hat\sigma_\beta=-\hat\sigma_\beta\sigma_\alpha\hat\sigma_\mu +2(g_{\mu\beta}\hat\sigma_\alpha-g_{\alpha\beta}\hat\sigma_\mu-g_{\mu\alpha}\hat‌\sigma_\beta)$

Bernardo Meurer

@DavidZ Check the question. there was an issue in memmove, fixed but the issues remain

But now the problem seems to be memcpy not correctly saving the board

0celouvsky

@ArtOfCode hello

ArtOfCode

00:17

o/

David Z

@BernardoMeurer huh, making the change in memmove fixes the segfault for me

0celouvsky

@ArtOfCode I'm wondering if Bernardo will try to shoo you away :p

Bernardo Meurer

@DavidZ Yes, but the history doesn't seem right

0celouvsky

Do you know C?

Bernardo Meurer

@ArtOfCode Do you know C?

If you don't shoo

David Z

00:18

@BernardoMeurer how do you know though?

ArtOfCode

@BernardoMeurer I spectate C debugging with amusement, but no, I don't know it beyond concepts.

Bernardo Meurer

@DavidZ Because the cells in board can only hold values 0-23. If the value is higher than 23 an error is thrown

And I'm getting that error

meaning board is receiving weird, high, values

which sounds like storing an address instead of a value

@ArtOfCode Shoo

David Z

Oh, that's not part of your MWE though is it?

0celouvsky

Be Nice.

ArtOfCode

@BernardoMeurer uhh... what?

Bernardo Meurer

00:20

@DavidZ Nope, I will amend it, one moment

0celouvsky

@ArtOfCode He's not afraid of you

ArtOfCode

Um... Good?

0celouvsky

then all is well I guess

ArtOfCode

well that was strange

0celouvsky

that's like, your opinion, man

Bernardo Meurer

00:26

@ArtOfCode We're not afraid of bullys like you

David Z

@BernardoMeurer it's not appropriate to be calling someone a bully in public

Bernardo Meurer

@DavidZ Hmm, I cannot get the error to show in captivity

only in the wild

David Z

weird

although that's how it seems to go with memory errors

Bernardo Meurer

Let me run it through valgrind

==3021== Invalid read of size 8
==3021==    at 0x4C2F5D0: memcpy@GLIBC_2.2.5 (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3021==    by 0x402283: boardSave (main.c:536)
==3021==    by 0x401461: main (main.c:122)
==3021==  Address 0x2330e0c0 is 16 bytes after a block of size 48 in arena "client"
==3021==
==3021== Invalid write of size 8
==3021==    at 0x4C2F5D5: memcpy@GLIBC_2.2.5 (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==3021==    by 0x402283: boardSave (main.c:536)

Ta-daa!

ArtOfCode

I seem to have been Cing a lot of C recently...

0celouvsky

00:31

Do you mean seeing?

Bernardo Meurer

@ArtOfCode Please go to your room

Please

ArtOfCode

@BernardoMeurer I'm in it

but honestly, I only came over here in the hope of finding some interesting discussion going on, you don't need to be defensive :P

Bernardo Meurer

@ArtOfCode You're a sound engineer?

ArtOfCode

Aye

Bernardo Meurer

That's cool

I quite like audio

ArtOfCode

00:39

Live production is great fun

Bernardo Meurer

I more enjoy listening at home

ArtOfCode

heh, there's that

Bernardo Meurer

Pretty much the only things I own are audio stuff lol

0celouvsky

@ArtOfCode we can talk about spinors or differential equations

ArtOfCode

@0celouvsky I would happily spectate ;)

0celouvsky

00:41

Or spinor valued differential equations but I don't have any liquor for that

Zophikel

Let $(x^{i})_{i \leq i \leq n}$ be coordinates on $\mathbb{R^{n}}$, $(y^{a})_{1 \leq a \leq m}$ be coordinates the components of the functions $\Psi$ and $\Phi$ can be written as follows.

            ^ Anyone tell me why this isn't rendering

     Have no idea

David Z

@BernardoMeurer ah, that's probably the same thing I turned up - some pointer being overwritten or something inside boardSave

Anyway I have to go for now

Bernardo Meurer

@DavidZ Nice discussion in the comments of the question

Getting closer to figuring it out

David Z

I'll come back and check it out later

Bernardo Meurer

Cool, see ya later!

Slereah

01:01

@0celouvsky cooltopic

@0celouvsky sounds like a job for google and "pauli matrices properties"

or "identities"

0celouvsky

So do you wanna read Struamann or not

Slereah

Lemme see

positive mass theorem?

Well I could use to learn it

0celouvsky

01:47

@Slereah it seems pretty technical

Spinor fields are horrible

Slereah

Are they

I mean they're a bit touchy to keep track of

what with the weird indices and commutation rules

they're not that bad

0celouvsky

Straumann uses the principal bundle terminology

Koolman

@heather don't know the site is not working

physics.qandaexchange.com

and don't know where is @Kenshin

I think he has gone for the trip , but don't know when he will return

Slereah

Straumann also goes all tetrads on this chapter

Cows

02:08

people laugh at suffering until they meet a situation they can't overcome

Suffering has left

years have passed,

knowledge, and happiness fill my being

I am with myself and myself know me and truth

Not so random thoughts about life

not random at all

It looked like magic, and I seemed stupid because I was without knowledge.

Without a proper tongue to communicate, and not of thy feathers

It was but a tongue and notes that labeled me a fool

I have earned a tongue too many from my journeys through the abstract

I hold myself till I get to a podium to share the tales

The tales of the abstact

It's ok, Nothing broke

Nothing is broken, but much was learned

about life, people, and the abstract

Bernardo Meurer

@Cows Have you met @Secret ?

Cows

@BernardoMeurer you mean in real life?

@BernardoMeurer no, I don't know anyone here in person

@BernardoMeurer but I am sure I have run into him here before

Eh had a little moment with myself, and my poetic side

Sir Cumference

02:28

Who wants to hear a programming joke?

Cows

me

Slereah

if you have to ask your joke is probably not strong enough to stand on its own merit

Cows

good one lol

@SirCumference do you wan to to discuss programming

Sir Cumference

@Slereah I gotta ask, are you a grad student or do you have a degree above a BS?

Wait that didn't make sense

Slereah

I don't understand the difference

Sir Cumference

02:33

I'm tired

Slereah

Are grad students not people

I have a master degree.

Sir Cumference

@Slereah Neat

You doing a doctrate?

Slereah

nope

Yashas

@BernardoMeurer !

Yashas

03:02

@BernardoMeurer Why do you allocate memory for UNDO_DEPTH boards? You can do it more efficiently. You can store the moves in a stack. Each time a move is undone, you decrease the stack pointer.

int moves_played[UNDO_DEPTH][2], current_index = 0;

when you play a move:

moves_played[UNDO_DEPTH][0] = column which is to be changed

moves_played[UNDO_DEPTH][1] = changed to what

dmckee

@Yashas He's working in raw c which means implementing a stack is an exercise in and of itself. (Though one any experienced c programmer can do at least two ways without much thought.)

Yashas

current_index++;

dmckee

Meh. That was a tree. I don't seem to have a golfed stack. Do have list and trees though.

Koolman

What is serial voting reversed

Slereah

gnitov laires

dmckee

03:11

Take it back. There is a stack here: codegolf.stackexchange.com/a/229/78, though it is a boring statically allocated array variety.

Yashas

memmove(**history + 1, *history, (UNDO_DEPTH - 1) * sizeof(***history));

the first dereference gives the pointer to the ***history

I think you need the location of the location stored in ***history

you are writing to some random memory

dmckee

I don't know how I can possibly be dyslexic about 'b' and 'p' when I am typing, but I manage it.

Yashas

Koolman

@dmckee what is serial voting reversed

dmckee

@Koolman Someone voted for (or against) a group of your posts in a way that the script considered suspicious. Those votes have been automatically rescinded.

Koolman

03:20

okay thanks

dmckee

Or maybe you voted that way on someone else. Not sure if it notifies you when your votes crossed the threshold.

I can think of a reason for it not to.

Koolman

it notifies me +24 serial voting

Fawad

@dmckee how much is threshold for it?

Cows

03:36

hehe got temp banned

will be well behaved now :P

dmckee

03:54

@Fawad Mere site moderators are not privy to such rarified data.

Plus I suspect that the site team is monitoring and tweaking it.

So that anyone who deduces the answer and then tries to exploit it will get caught out eventually.

(Not letting you easily measure the answer, is the reason for not telling people when their votes have been canceled that I alluded to earlier.)

Best policy: don't go hunting through another user's profile in search of stuff to like or dislike; just vote on what you encounter as you navigate the site.

vzn

04:19

@Kaumudi.H hey you easily have more than 5 cyberfriends on here already. btw shog9 just agreed to send out tshirts for participants! on other hand he doesnt have JRs experience shipping to india... o_O chat.stackexchange.com/transcript/13775?m=36702802#36702802 ps thx to whoever starred the invite :)

user228700

@vzn Participants in what, exactly?

vzn

@Kaumudi.H (hi!) did you click on that meta link describing the hbar AMAs? by DS? fyi heather was our last guest, thought it went great :)

user228700

Hi :-) I did! I've read that one before; I know what an AMA is.

user228700

But this is what JR said... :-|

user228700

23 hours ago, by John Rennie

I would guess tht your main contribution would be a perspective on what it was like for students preparing for the JEE, and that topic is not universally loved by the chat members :-)

vzn

04:27

@Kaumudi.H uh, JR was invited to do it long ago, he shied away/ declined, so the question is, do you have more cojones than JR who motorcycled across europe? and probably have at least as interesting stories? nobody ever said it had to be about physics, & think youve been damned by his faint praise as the english expr goes... o_O

user228700

I wonder why he declined...

user228700

Anyhoo, like I said before, I'd be happy to do it as long as people are happy to ask and listen!

vzn

@Kaumudi.H lots of ppl have declined, its a thxless/ lately near-impossible job trying to get ppl who like to chat, TO CHAT @#%& :P :(

user228700

Huh :-|

vzn

@Kaumudi.H thats way cool. ok our tradition/ convention is that you write up a meta post describing your talk (meta post has links/ examples) & pick a time & thats all thats nec. the regular biweekly mtgs work well if you can attend that slot... have you ever been to one?

Slereah

04:29

why does Krasnikov uses the star of Deneb as an example destination

is there something remarkable about it

user228700

@vzn mtgs?

vzn

@Kaumudi.H meetings

user228700

Ah, the chat sessions?

vzn

@Kaumudi.H yes there is usually a sizeable built-in audience, think even more if you advertise your talk, DZ has no problem with that slot for guests

@Slereah ask alice & bob maybe they know :P

user228700

Sheesh. I've read Heather's post and feel overwhelmingly under-qualified. Really, who is interested to hear from me other than you and blue? :-P

Slereah

04:35

usually people use Alpha Centauri when they want to talk about a fake trip to the stars

Cows

I heard Physicsoverflow has something called paper review. How does it worl

*work

just curious

Does this site have something similar?

vzn

@Kaumudi.H argh, the whole modesty thing, modesty is the enemy of the spotlight... think about it like this, you like to chat, right? its just a chat. think of how many ppl youve chatted with in here. think of how long youve been on the site. think of what drew you to it. think of all the things you talked about here in the past. how about highlights? etc? btw youre what, 4yrs older than heather? etc! sheesh ask slereah, he'll tell you, ITS FUN =D

user228700

:-) But I haven't at all contributed to the main site in any significant way like heather has.

user228700

I dunno how old Heather is but I turned 18 last week.

vzn

@Kaumudi.H yeah, isnt it great? it doesnt matter :) look, if you can tolerate a bunch of ("mostly yang!") cyber physics geeks, they can surely return the favor right? =D ... you havent given up on your dream of being a physicist have you? or did your mom persuade you to be more practical? and even if she did, it shouldnt stand in the way of a nice chat session :)

user228700

04:40

It's not so much modesty as a fear of sorts that...well, that nobody would want to listen about what I have to say because nobody else has shown any interest at all. Please don't get me wrong; I feel that it's an honor to have been asked by you and I'd gladly oblige but do u see where I'm coming from?

vzn

← sigh, dons cheerleader dress and waves pom poms furiously YOU GO GIRL! =D

Slereah

Now consider an experiment with two possible results.
Example 1. A device set on a spaceship first polarizes an electron in the y-direction and then measures the x-component of its spin σx. If the result of the measurement is σx = +1/2, the device turns the spaceship to the right; otherwise it does not.
Example 2. A device set on a (very massive) spaceship tosses a coin. If it falls on the reverse the device turns the spaceship to the right; otherwise it does not.

One of those seem a bit cheaper

user228700

@vzn :-P

vzn

@Kaumudi.H plz realize this is a mere )( psychological block, obviously many are interested in what you have to say from long history in the chat transcript, there are probably hundreds of msgs, maybe over a thousand of evidence! we would be honored to have you :)

user228700

:-D When's the next chat session?

0celouvsky

04:44

@Slereah so do you wanna do chap 9 or not

vzn

@Kaumudi.H are you still studying for the JEE? thats plenty of physics. you might have something to say about physics vs engr vs science; its remarkable in india that the entrance exam is the same for each. etc

0celouvsky

JEE has zero physics

user228700

@0celouvsky Dude -_-

0celouvsky

what

Cows

what is JEE?

vzn

04:44

(lol you may have to deal with the peanut gallery of which you are well familiar)

user228700

@0celouvsky That's just incorrect.

John Rennie

Oh my goodness. JEE arguments again.

0celouvsky

@Cows Joint Extermination of Eucalyptus

@Kaumudi.H you're incorrect

vzn

@Kaumudi.H next physics mtg is in 4 days next tues but you could prob schedule the next meeting. can you deal with the timezone difference? let me look up date/ time... sometimes insomnia comes in handy right? (JK! sort of!)

user228700

@0celouvsky Sure I am. I'm actually sort of frustrated now; I don't understand why you are whining about JEE when it's us who are suffering under this terrible system.

Slereah

04:46

@0celouvsky sure

0celouvsky

@Slereah this $S^2_\infty$ stuff seems reaaaaally fishy

@Kaumudi.H you don't have to make me suffer too

Cows

@0celouvsky nice one. I just read that its an entrance exam

user228700

Don't read our messages! God knows I don't read your messages about Math.

Slereah

I guess it's supposed to be $\lim_{r \to \infty}S^2_r$

user228700

@vzn Hmm. Would it be OK if we could postpone it until after my exams get over? .__.

0celouvsky

04:49

@Slereah how is $$-\frac{i}{2}\int_{S_\infty^2}\phi^\dagger\hat\sigma\wedge \nabla\phi+(\nabla\phi)^\dagger\wedge\hat\sigma\phi$$"clearly real?"

oh wait

maybe I should take the adjoint :P

vzn

rats removed that by accident

0celouvsky

I guess it is clearly real

Slereah

Yeah it seems """hermitian"""

0celouvsky

@Kaumudi.H what?

vzn

@Kaumudi.H tues may 2nd, 2nd next mtg... hey you dont stay away from chat just because of exams right? its 1hr long, no preparation needed. when are your exams?

Slereah

04:50

He writes a spinor field as $\phi$

Not cool

user228700

Right, but I'm not going to be home for a while so I'm not going to be on here as much as before starting this weekend.

0celouvsky

what's a spinor supposed to be?

vzn

@JohnRennie @#%& did you say something to dissuade the young lady from leading an AMA? shame on you :P

user228700

@0celouvsky What about that sentence doesn't make sense?

Slereah

A section of the associated spin bundle or something

0celouvsky

04:51

@Kaumudi.H Why wouldn't you read it

@Slereah I mean what is the symbol supposed to be in your mind

user228700

@0celouvsky 'Cause I don't understand any of it.

0celouvsky

That's the problem with JEE

Slereah

@0celouvsky $\psi$ or $\chi$

0celouvsky

@Slereah ah, $\psi$ is a Dirac spinor

why the fuck does everyone think that I'm a topologist

holy crap it's pretty annoying

vzn

@Kaumudi.H good topic for the AMA :)

Slereah

04:53

The Weyl spinors you write as $\psi_L$ and $\psi_R$

user228700

@0celouvsky Because you bring up Topology all the time!

vzn

@0celouvsky doubt you could pass it :P

user228700

@0celouvsky Never mind. I can't be bothered to argue about JEE; I wish you'd stop complaining though, when you don't even have to endure all this like the rest of us; it's insensitive of you to complain because this phase of our lives is incredibly difficult for us and you don't know what that's like.

0celouvsky

@Slereah Ok, I think what he wants is to take $\Sigma=$ increasing union of balls $B_r$. Then by various measure theory things, $\int_\Sigma=\lim \int_{B_r}$. Then he uses Stokes, and writes $\int_{S_\infty^2}=\lim \int_{\partial B_r}$

Slereah

I see

Yashas

04:55

@0celouvsky What's the problem?

0celouvsky

@Kaumudi.H 1. No. 2. Topology is not a proper noun.

Slereah

"assume that the dominant energy condition holds"

That's a pretty specific condition

0celouvsky

@Yashas JEE leaves no time for exploration of other topics

@Slereah you're looking at theorem 9.1?

Slereah

yes

John Rennie

@Kaumudi.H Ryan is saying that the content of the JEE is of no use for anyone wanting to learn matematical physics. This is true, but unhelpful, since (a) that's not what the JEE is for and (b) students don't get to choose what is in the JEE.

0celouvsky

04:56

yeah it was 9.20 that gave me the hint

$\Sigma$ doesn't really have a boundary, but it does have a "limit of boundaries"

I mean $\Sigma$ could be just $\Bbb R^3$

Yashas

@0celouvsky JEE is for high school students

user228700

@JohnRennie Exactly. It's not as if we don't realise that the syllabus and the way that it is explored in under 2 years is crap. We don't have any choice!

Yashas

what do you mean by other topics?

JEE syllabus is already vast; you might have to square (or cube) AP syllabus.

2

vzn

@Kaumudi.H this tells you the local time of the mtg, think it is 1600Z chat.stackexchange.com/rooms/info/71/the-h-bar?tab=schedule gotta go soon, thx for the consideration, if you feel a moment of spontaneity/ yang boldness, go ahead & post to meta for may 2nd, for sure will upvote it myself :)

0celouvsky

@Yashas and yet @Kaumudi.H cannot understand any of the basic math I discuss in chat

@Slereah Why does the curvature involve Pauli matrices?

John Rennie

04:58

@Kaumudi.H Absolutely, and it's natural to feel annoyed when someone appears to be criticising you personally and denigrating the huge amount of work you've put in. But although he is being annoying, that is not what Ryan is doing.

Anonymous

@Yashas Need some help

Anonymous

You there?

Yashas

@blue ?

0celouvsky

If anything I am saying you should rebel and burn down the government

vzn

@JohnRennie lol ryan is quite critical in general. ofc thats what hes doing :P

Slereah

04:59

@0celouvsky I am not quite sure

user228700

@vzn I will. Thank you for considering me :-) Sorry for the late responses!

Slereah

mb I should first read the appendix

"Spin structures and spinor analysis in GR"

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