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7:05 PM
@loltospoon Hello
 
@HsMjstyMstdn hello!!
 
Can you define a metric on non-paracompact manifolds if you define the metric as a map $$d : M \times M \to \Bbb L^+$$
for very long distances
Only $\omega_1$ km to drive and we're there
 
7:20 PM
@Slereah wot
If your observable has symmetric compact resolvent, then $\psi =\sum a_i\psi_i$, $a_i=(\psi,\psi_i)$ is exactly right.
 
You'd think there would be integrals and measures and whatnot involved
Also what is a symmetric compact resolvent
 
It's a resolvent that happens to be compact and symmetric, I'd guess
 
The resolvent is $(E-H)^{-1}$
 
@dmckee Are you there?
 
You need that to be symmetric (it is if $H$ is) and compact for some $E$
I guess observables are automatically symmetric
 
7:24 PM
@BernardoMeurer Sorta. What's up?
 
$H$ the operator and $E$ the eigenvalue?
 
$E\in$...probably $\Bbb R$.
It's clearly NOT an eigenvalue.
Else $(E-H)^{-1}$ doesn't exist.
 
I guess it would be a division by 0 else
 
@dmckee I just fixed it
I was screwing up mallocs of structs
 
@Slereah so what do you mean?
 
7:28 PM
I was just wondering if it was one of those things that is done terribly unrigorously in physics
 
most probably
 
because not every operator has an eigenbasis
 
Does it count if it has one in the rigged hilbert space
 
then who knows
 
7:30 PM
hm, what notation to use for the Hilbert product
I already have $\langle , \rangle$ for the Minkowski product
Maybe I should use $\eta()$ instead
 
Clear from context
 
mb
 
Use the same symbols
 
Hm
Trying to think of any context where both might be used in the same formula
like the product of expectation values or something
Maybe for the momentum
$\langle \langle p \rangle, \langle p \rangle\rangle$
 
@blue Say, aren't you from Bengal?
@Yashas Same question^
@Aryabhatta Um...same question again.
@Koolman And yeah...same question.
@SwapnilDas Same question bud^
 
7:44 PM
@Slereah use () for metric <> for inner product
Oops
Wrong way around.
 
maybe
we need new brackets
 
If there's any one from Bengal out there: @Always proposed a Bengali language SE, and it needs support NOW! So...um...do your thing and assist him in his noble endeavor!
Oh, hey @Slereah o/
 
$\lmoustache \psi, \psi \rmoustache$
 
Can I ask a question about something simple I just can't get straight in my head
 
@Slereah This statue was in my undergrad university, in front of the mathematics department
 
7:48 PM
I can't fully get Equivalence classes straight in my head, why do equivalence classes $E$ and $E'$ have to be either equal or disjoint?
 
@Slereah I'm on mobile. That better not be an actual thing
 
use the transitivity of equivalence to show it
 
I can't spell that word
My phone keeps autocorrecting incorrectly.
 
@paracetamol I feel ambivalent about a Bengali language SE so I am not going to vote for it.
 
@BalarkaSen Awww, why not?
You're from WB aren't ya?
 
7:53 PM
Why not what?
 
@BalarkaSen Support La Revolution
 
The hell?
Please don't speak in non-sequiturs
 
@BalarkaSen You're from WB. It'd be nice if you'd support your fellow Bengali's endeavor ._.
 
I certainly don't support every fellow Bengali's endeavor for the sake of my actions being nice. On the other hand, I just said I feel ambivalent about it - I am neither for or against a Bengali language SE
In which case, I won't vote.
 
Sighs
 
8:02 PM
Site for Bengali Language SE? What is so special in that language which will give productive results to human resource? Are interviewers communicate in Bengali? That's a sad reality that people try to promote their own regional language which is spoken only in one state of India
 
Additionally, for anyone who's interested:
27
Firearms

Proposed Q&A site for hunters, target shooters, personal defense carriers, gunsmiths, gun enthusiasts, and all other firearms questions.

Currently in definition.

 
@defalt That's too extreme. Certainly it's not the most used language of communication in the world or something, but some of the finest literary or artistic works (not only in India) are written in Bengali, for example.
And I am sure that's true for a lot of other regional languages too, I am just not familiar with them.
 
Even if those artifacts were written in that language, only those artifacts have value, not the language.
 
strong opinions on Bengali for someone who just entered a physics chatroom
2
 
@defalt I'm...not from Bengal ._. I simply jumped in the wagon, because I know for a fact that there are several Bengali SE users I've encountered, and that this proposal seems like a good idea...just need a bit of direction ಠ_ಠ
@Slereah :D
 
8:08 PM
@defalt That's a strange thing to say. How can an artifact written in a language be thought of as disjoint from the language? Certainly a translation of a poem in, say, Russian wouldn't have the same artistic quality as the original one, for example.
That's true for any literary works in any language whatsoever.
 
why does this guy hate bengali so much?
a salty indian maybe?
 
Who are the enemies of the Bengali
 
What is fair to say is that Bengali doesn't have much value as a language of communication beyond Bengal :P But that doesn't make it of no use.
 
why would anyone show interest in that regional language which is not even national and is only spoken in one state which has no productive value for human resource?
 
oh jesus christ
 
8:10 PM
The old GDP argument!
 
you're not convincing anyone here
@Slereah hmm
 
how does Bengali increase the GDP
 
you're right
 
@defalt You're talking in circles. I just gave you a productive value for human resource.
 
I don't hate Bengali but a suggestion to have SE for it for international learners is too much to be considered
 
8:12 PM
There are probably more Bengals than Jews and they have their own SE
 
I'm guessing it will just be like every SE board
It will be tested to see if it generates enough interest
And the free market will decide
 
I have no opinions about a Bengali language SE. But that certainly doesn't mean I consider Bengali to be a useless language!
 
SE is hardly a free market
My name is terrible
I should change it
 
Ooooh! 'Bout 15 million Jews and over 90 million Bengalis :O
 
interesting
not sure how i feel about that :P
 
8:15 PM
2 mins ago, by 0celouvskyopoulos
There are probably more Bengals than Jews and they have their own SE
 
Correct.
I am a friend of the Bengali.
 
@0celouvskyopoulos Sure you are, buddy ;)
 
Certainly not your friend.
 
@0celouvskyopoulos I'm not Bengali .-.
 
what is judaism's position on quantum interpretation
Does God know the state of a particle
 
8:16 PM
You'd probably be stoned for asking the question, no?
 
Maybe by the ultra orthodox
they are a tense bunch
0
Q: Is Science/Scientism a form of Idolatry?

rayIn the scientific community (and much of the secular world) there are many who adopt an outlook whereby one need not believe anything which cannot be demonstrated using the scientific method. i.e. it must be repeatable through experiments and explained through cause/effect scientific principles. ...

 
@paracetamol here you are only half correct..Those several Bengali users are first Indian and then they are Bengali..This is not a racist comment..This is how you represent yourself internationally..you first belong to a country and then belong to its state
 
How does Isis view QM?
 
please keep the nationalist bickering out of the chat
2
 
@Slereah I was also surprised to see such recommendations for SE in physics chat
 
8:19 PM
lol this is becoming a weird conversation
 
@0celouvskyopoulos I imagine they'd just discard relativity, saying Allah has the privileged reference frame, then just say quantum mechanics is a western devil used to obfuscate the tunneling powers of mohammed
 
3
A: Does the Torah 'know' about 'quantum mechanics' and 'DNA synthesis'?

HaLeiViI'm not sure what you mean by "the Torah" knowing. The Torah was given from Hashem, and He is obviously aware of how He made the world. The Torah won't be saying something that is not true. Therefore, it can't be saying something that is the opposite of true scientific discovery. As far as if al...

1
Q: Must we believe in a hidden variable for quantum indeterminacy?

ZelzugeEspecially regarding quantum indeterminacy. Adding a bit more info as requested. "God does not play dice", I quote Einstein. He said those words when in an argument with another scientist that was in support of quantum mechanics while he, himself wasn't. He proposed that there was a hidden var...

:D
 
...this book was $1.90 back in the 80s
how is that even possible
 
HE used to be way cheap, too
I think during the 90's or so the publishers started jacking up the price of books way up
 
my advisor always writes the prices of books in them for some reason
he has some books for $30 that are $100+ now
 
8:26 PM
"If we find such a variable, it will not be the variable of Allah swt. Just a mathematical symbol."
1
Q: Could Allah be a Boltzmann Brain that evolved spontaneously from the uncertainty of the quantum vacuum?

Justin WatersA Boltzmann brain is a hypothesized self-aware entity that arises due to random fluctuations in the quantum vacuum. Does Islamic theology allow for this interpretation of Allah? https://en.wikipedia.org/wiki/Boltzmann_brain

"Even if there are totally random decisions in the universe, they hold possibilities only for those who are in the time line. Allah is beyond that, thus he can know."
Dammit Allah, I need to know that quantum state!
 
^ I'm not sure if it'll be a good idea to star that...but I like it :D
 
14
Q: Reconciling the evidence for the Uncertainty Principle with belief in an omniscient G-d

AdamRedwineOne of the foundations of modern quantum mechanics is the Uncertainty Principle. This principle is not an assumption, but rather is derived from assumptions made with regard to the structure of nature. The basic statement of the Uncertainty Principle, however, is that it is impossible to know the...

Let's check the christian SE's opinion on quantum mechanics now
 
Rubs hands in anticipation
 
Yep, never be narrow minded about a specific religion
 
38
Q: How do Christians understand the omniscience of God in relation to the Uncertainty Principle?

AdamRedwineOne of the foundations of modern quantum mechanics is the Uncertainty Principle. This principle is not an assumption, but rather is derived from assumptions made with regard to the structure of nature. The basic statement of the Uncertainty Principle, however, is that it is impossible to know th...

 
8:31 PM
:O
Oooh, try Buddhism next!
Wait...it's the same idiot posting the same question ._.
 
2
Q: What are the similarities between quantum physics and buddism?

krishnaWhat are the similarities between modern physics/quantum physics and Buddism? Although i know little about this, like Budha said that conciousness creates everything, emptyness and dependent origination kind of things. What are other things that matches with what modern science is saying?

Odd question
"As far as I know quantum physics does not teach four noble truths, dependent origination and consciousness."
 
> However quantum physics can be used as examples to explain Buddha's teaching.
 
"Relational quantum mechanics agrees with the Buddha's insight into anatta."
Congrats, Rovelli
You are enlightened
 
OOOH, do Hinduism.SE next!
@Slereah Meh :3
 
2
Q: Is there any verse in Vedas explaining Instantaneous Action at a distance

Srikanth ReddyI'm a Theoretical physicist rather than that I am a Hindu.These days, I'm on my research on Quantum Entanglement. This simply says that "An event at one place can instantaneously event at another place arbitrarily far away faster than light" On my quest on my research I saw this verse in Vishnu S...

closest one
 
8:35 PM
Close, yeah :(
Disappointed
 
8
Q: Mechanics and methods for playing a quantum-superposition of worlds

AnaphoryI'm looking for game mechanics and story telling methods that convey the atmosphere that characters don't just live in one world, but in a multiverse adhering to something similar to the many-worlds interpretation of quantum mechanics. This should in particular imply that if a character's action ...

The RPG SE opinion
 
I don't think I like that person...he just ruined RPGs for me ._.
 
That $\Delta|\nabla f|$ thing is in this book
 
Goodbye Runescape o/
 
8:37 PM
200 pages after it is used
 
Sniffs
 
what does worldbuilding SE say tho?
 
There doesn't seem to be any more religious SE
Where's the Zoroastrian stack exchange
plenty of quantum questions there
What to use for QM
Just letters or kets
I think kets
 
I've heard using kets is illegal
 
It will help avoid ambiguities
 
8:42 PM
Its like a class A drug
 
I've got enough symbols as it is
 
@dmckee Still here?
 
Sorta. I'm grading homework. Thrill a minute stuff.
 
@dmckee I'm doing code which uses pointers to a struct I wrote, to try and make an array of sorts, but it's broken as all hell. Check this out
@dmckee This is the code
This is what happens when I run it through valgrind
I suspect I am doing something wrong either in my allocation scheme or when referencing the struct objects
But I don't know what I'm screwing up here
 
You didn't check the return status of malloc in readPlanes. Bad coder! No Cappuccino!
 
8:57 PM
@dmckee yeah, yeah I forgot there :P
Sorry
@dmckee Fixed
@dmckee Refresh the gist
 
It's been some time since I looked at the output of valgrind.
 
"Hello darkness my old friend"
 
good song
 
o/
 
@dmckee I updated the valgrind output to a more sane example. Where you can see how the plane at fleet[1] is totally bonkers
 
9:02 PM
Do you know sizeof(plane) right off? The original valgrind output had 40 bytes lost in 2 blocks and I'm trying to use that to help guess where the failure might be.
 
@dmckee What do you mean by if I know it "right off"?
 
The new valgrind output has the same. Did the input change? If so it means the failure is not tightly linked to the particulars of the input.
 
hi @Danu
 
The input did change, yes
 
@BernardoMeurer Well. I suppose tht's just a polite way of asking you to ask the debugger.
 
9:04 PM
@dmckee If I do printf("%zu\n", sizeof(plane)); I get 24
 
@BalarkaSen How are you doing? Busy lately?
 
Yeah. I think line 37 is a problem. You didn't free the allocations from line 63 before freeing the one from line 59.
Or did I miss something?
 
@Danu More or less fine. Yeah, been learning lots of things about foliations.
Also trying to learn Riemannian geometry but I'm meh at it
 
Mhm
 
Usually you would write a routhine freeFleet to take care of that for you.
 
9:07 PM
If you have some time left over during the coming weeks I'd love to have someone read the parts of my thesis I've written so far @BalarkaSen... ;D
I need to send them to Bonn by the 15th of May for my application
 
@dmckee Ah, I see
 
If first walks through fleet[i] freeing individual planes before freeing the array.
 
Haha, afraid they're too hard for me. I don't know anything about complex geometry. Good to hear that you're writing up stuff though!
 
Classical mistake and exactly the sort of thing that RAIL is suppose to save you from in c++.
 
@BalarkaSen It's not complex geometry
Right now it's just background material
 
9:08 PM
I see.
 
it's not very difficult stuff
I'm mostly just combining results from different textbooks/expository papers
I think it'd be relatively easy for you
 
@dmckee Fixed, but the problem persists
 
Do you still have access to my dropbox folder?
 
I'm having a look. thesis-main, right?
 
I think that didn't matter since it's at the end of the main function. The memory will be freed anyway
for(int i = 0; i< size; ++i) free(&fleet[i]);
free(fleet);
 
9:09 PM
Ya I have access
 
yeah
 
This seems silly though
 
I've written on (i) homogeneous spaces (ii) background on flag manifolds/octonions
 
@BernardoMeurer Well, yes, but valgrind will report it as lost.
 
I plan to write out that second part in the coming days, then put in the computation of the cohomology ring (at least the part that is complete) of some spaces
 
9:10 PM
oh oh homogeneous spaces. I need to understand them better.
 
And you should definitely be in the habit of making your opaque types clean up after themselves.
 
@dmckee Alright, let me re-run valgrind
 
then the Chern number stuff, but I don't need you to proofread that
@BalarkaSen The stuff I wrote is mostly about some special topics, but see what you think
 
I'm probably a bad proofreader if that's what you want! But I can always have a look at cool stuff
 
Right now it's just G-invariant metrics
@BalarkaSen Well just see if you like the exposition
and maybe you'll catch a typo or two...
 
9:11 PM
@dmckee Updated valgrind log and code
@dmckee That doesn't work though
that weird memory free makes the code and in SIGABRT
 
reading
 
Most likely because I'm freeing memory that was already free
 
So ... if you said the problem persists before you had re-run valgrind then you must have some other symptom. What are you seeing.
 
@dmckee Okay, let's go over the problem carefully
It's very weird in nature
So, a plane has elements ID, model, fuel
 
@BernardoMeurer Well that for(int i = 0; i< size; ++i) free(&fleet[i]); should be for(int i = 0; i< size; ++i) if (fleet[i]) free(&fleet[i]);
 
9:14 PM
Which are set on read plane
 
Otherwise you free blocks that haven't been allocated in the first place.
 
@dmckee That doesn't work because fleet[i] is a plane I can't do that free-ing with it
 
@Danu When is a quotient of two Lie groups homogeneous? Is there a general criteria?
 
because if(fleet[i]) is the same as if(fleet[i] != NULL) and that makes no sense when fleet[i] is a plane
 
@BalarkaSen You get a manifold when you quotient out a closed subgroup
(is that what you're asking?)
 
9:17 PM
That's true; when does that admit a homogeneous metric?
 
@BernardoMeurer Then look closely at what line 65 is doing.
 
That quotient manifold
 
@dmckee Yes, agreed
 
I am asking for some sort of corollary of "$M$ is homogeneous => $M$ is diffeomorphic to $G/H$"
just as a side
 
The problem for me is, that is only there because I cannot allocate my "array" of planes otherwise
 
9:19 PM
You allocated the array of planes in line 61.
The storage for those size planes now exists. You just have to fill it in.
But that doesn't leave you with a problem representing null data in the middle of the list if they can be deleted later.
 
@BalarkaSen ah, you mean to ask about when $G$ acts by isometries?
 
@dmckee They cannot be deleted, that's no issue
It's a one-time thing
 
@Danu Right, yeah.
 
So wait
over in main
fleet should be a double pointer?
That's the issue?
 
I have no idea, to be honest. I don't know anything about the Riemannian category :P I probably should.
 
9:21 PM
So ditch line 65 (and therefore also the line 38).
 
That's fair; I don't either
 
I'm just working with the definition from Besse because it makes the proof that symmetric spaces are homogeneous easy
and I thought I would want to have that
there are some subtleties about the definition
 
@BernardoMeurer To allocate the way you were it should be a ragged array. But you don't need it to be a ragged array. Just a ``dynamic array''.
 
for instance with this definition the group has to act effectively (no element except $e$ acts trivially)
 
@Danu Aha! See! now it breaks!
I get a SIGSEGV
 
9:22 PM
but that assumption can actually be dropped and is not fulfilled in many examples that one typically considers (because of the center or something)
 
after I input the ID for the second plane it explodes
 
Ah alright I see
 
but you can always find a corresponding situation where the action is effective or something
it's kind of shitty and I would rather just not deal with it
but I probably should at some point
 
Yeah there are multiple ways to think of a homogeneous manifold as a quotient of groups
 
In any case, I'm mostly interested in compact, semisimple Lie groups
in that case we're always good to go because you have Ad-invariant scalar product on the algebra
 
9:24 PM
@dmckee Lemme update the code gist and valgrind again
 
then you can make bi-invariant metrics for sure
 
Well you have to change all the fleet[i] = ... to (*fleet)[i] = ... or some such.
 
I explain later on how to construct invariant metrics
 
That's an exercise in do Carmo, @BalarkaSen.
Hi @Danu
 
they're given by inner products on $T_{eH}G/H$ invariant under the isotropy representation
 
9:25 PM
Because in readPlanes fleet is a plane**, and the thing you call fleet in main is one indirection away.
 
@Danu Yeah I'm looking below
 
@dmckee Aha!
 
@0celouvskyopoulos Which is?
 
@BalarkaSen Constructing a bi-invariant metric
 
(and you can get those from e.g. bi-invariant metrics on G)
 
9:25 PM
and damn that username man, it's so long
Ah ok
 
@0celouvskyopoulos We're talking about G/H
not about G
 
@Danu you're talking about it right here.
 
Yeah, which is not the main conversation :P
That's just the special case that I actually need
in any case
 
@dmckee Worked like a charm :)
 
Sure, but if Balarka doesn't know how to do it...
 
9:26 PM
Maybe you do kknow about this
 
Thanks man!
 
it's an exercise in the book he's reading
 
Do you know under what conditions you can guarantee that on G/H, G acts by isometries?
 
the book I should be reading anyway!
 
(I know that "reductive" suffices)
 
9:27 PM
@BalarkaSen Correct
 
I've done that before, myself. Once you get that ragged array pattern in your head it is easy to apply it where it doesn't belong.
 
anything weaker?
 
@Danu I don't, G/H scares me
 
In any case @BalarkaSen I'll ask my supervisor about the details
 
me too man me too
 
9:27 PM
@dmckee I just never had used an array of structs before, got a bit confused on how to make it work
 
but just put "reductive" in wherever needed if you're scared
 
I'm sure you checked Helgason, and I don't really care to know more about them then that.
 
Also, what's the difference (apart from syntactic ) between just a struct and a typedef struct @dmckee
 
@Danu Sure, got it.
 
Then $\mathfrak g=\mathfrak h\oplus \mathfrak m$ for some $\operatorname{Ad}_G(H)$-invariant complement of $\mathfrak h$ and everything probably works just fine
 
9:29 PM
If I declare a type struct thing {...}, then anywhere I want to use that type I thave to write struct thing aThing;
 
@dmckee So it's just syntactic
 
@BernardoMeurer Yep. Consequence of how the type table work. If I don't like typing struct all over the program I say typedef struct thing {...} thingT; so that thingT is an alias for struct thingT;
 
@dmckee Nice, good to know. How do you know so much C?
 
Lots of practice in a couple of spurts. Then I participated pretty heavily in Stack Overflow for a while which made me think about what I had learned.
 
Holy cow you have a C golden badge!
I hadn't noticed that!
and C++!
Cool, I am in good hands :P
 
9:35 PM
You can get those badges as a very low grade expert if you just answer enough questions. There are a lot of people on Stack Overflow who know those languages much better than I do. Even some members of the standards committees.
You really can get definitive answers from them which is really nice.
 
SO has some amazing answers
Have you ever seen the branch prediction vs unordered list one?
It's one of the best answers to anything ever
 
It's been a while, but I believe I did.
 
17738
Q: Why is it faster to process a sorted array than an unsorted array?

GManNickGHere is a piece of C++ code that seems very peculiar. For some strange reason, sorting the data miraculously makes the code almost six times faster. #include <algorithm> #include <ctime> #include <iostream> int main() { // Generate data const unsigned arraySize = 32768; int data[arr...

It's really cool
 
Yeah. That exposes just how bleeding complicated modern processors are under the hood.
There was a time when I knew the instruction set for the computer on my desk including how long each and every operation would take to complete.
 
Oh, I forgot to tell you, I'm getting pretty good at VHDL :)
 
9:37 PM
But that was a 6502.
 
lol
I still hate how you must design a project in VHDL, and the amount of needless code repetition is silly
But I'm in peace with the syntax and my CPU is fully functional
 
Cute little instruction set and fetching or writing something from memory always added one cycle.
 
at an amazing.... 25MHz!
 
0
Q: Is there a slick proof for the identity that expresses the inner product of imaginary octonions in terms of the cross product?

DanuConsider the octonions $\mathbb O$ and in particular their imaginary part $\operatorname{Im}\mathbb O$. Let $(-,-)$ be the scalar product induced by the identification of the imaginary octonions with $\Bbb R^7$. Furthermore, define the cross product of (any) octonions by $x\times y:= \frac{1}{2}(...

 
@BernardoMeurer Cool.
 
9:39 PM
Anyone know anything about octonions? :P
 
Not me. Keep meaning to find the time to learn.
 
It's not as bad as it seems at first
 
They're pretty decent
but very useless unless you're interested in some specific topics
 
Digilent has a really nice FPGA now, I'm getting it for my birthday, the Arty
100 bucks and pretty powerful
 
(I'm interested in $G_2$, which you can define as the group of linear maps that preserve the octonion multiplication structure)
 
9:40 PM
You should look into it, with Vivado it's pretty easy to learn
 
9:55 PM
@Danu I have a rather detailed and specific question about an inequality in a paper. Should I make a PSE post, MO, or email the author?
How many days should I sit on it before doing something
 
@0celouvskyopoulos Probably PSE first to see if it's easy
then email author
I'd almost never post on MO :P
Too ashamed hahaha
 

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