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2:02 AM
@Semiclassical "pure point spectrum"
 
$N \ge 3$?
 
oh, nice
 
the spectrum in the functional analysis sense consists of only eigenvalues.
no weird functional analysis BS going on, in other words
 
wait.. what?
 
2:04 AM
The specific case of interest for me is $L=-\partial_x^2+\alpha\cos x$ with periodic boundary conditions, btw
 
ah!
okay
so the eigenvalues are the point spectrum
if that's all you've got, the operator has a pure point spectrum
 
I know from experience that that's got a nice spectrum for real $\alpha\neq 0$
 
okay, I'm caught up now
now what?
 
But couldn't remember the terminology
eh, that's all I was asking :P
 
oh, well
fine, then!
 
2:05 AM
I can say more, though
My operator of interest is really $H=\begin{pmatrix} -\partial_x^2+\alpha\cos x & w \\ w & -\partial_x^2-\alpha\cos x\end{pmatrix}$
 
OH GAWD NO!
 
why is it called $H$?
 
Hamiltonian
 
that was my guess, but it doesn't exactly look like a Hamiltonian to me
 
2:08 AM
@Secret what is the question?
 
Well, in QM $p=-i\partial_x$ up to constants
 
yes, I have seen that before
 
So that's $H=p^2I_2+(\alpha \cos x)\sigma_z+w\sigma_x$
 
oh, doi
 
So it's the Hamiltonian for a spin-1/2 particle with a spin-dependent potential
 
2:09 AM
there is a negative sign there.
 
Where?
 
in the lower-right
I didn't pick up on in the first time round
 
ah, gotcha
$\sigma_z,\sigma_x$ are just Pauli matrices
 
2:10 AM
we are out of my depth
I have taken a grand total of two physics courses in my life:
 
$\sigma_z=\text{diag}(1,-1)$ and $\sigma_x=\begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$
 
in high school I took a combined pre-calc / newtonian physics class (that I bailed on half way through the year to go spend some time in Russia)
and last year I took a course in QM
 
Hmm, I stopped by to see if @Antonios was doing a good job subbing for me ... But I guess it's turned into physics. Hi @Semiclassic.
 
lol, i bet that was interesting
hi @ted
 
I got all the math stuff
just not why anyone cares :)
 
2:11 AM
lol
 
like, I have zero idea what the connection is supposed to be
 
Connection? Are we do doing connections? :)
 
Baez taught the corresponding classical mechanics class last fall, but my teaching load was insane, and I couldn't manage to fit it into my schedule :\
@TedShifrin Down!
 
@TedShifrin not unless this turns into me complaining about not understanding Berry curvature, no
 
LOL
 
2:12 AM
@XanderHenderson I bet Baez found a way to turn classical mechanics into category theory
 
Booo, hissss.
 
would not surprise me
 
I honestly doubt it
his grad level real anal class is pretty standard stuff
 
Here's why I like the operator I wrote above
 
I can't imagine that he CM class would vary from the typically syllabus by much
 
2:13 AM
I was just joking
 
heh
he's actually a really good lecturer, though his homework tends to lead-by-the-nose a bit
 
That was my one complaint about Guillemin's class and book. Gives away too much in the homework.
Otherwise, he was fantastic.
 
first off, when $w=0$ it becomes diagonal. Moreover, the two operators along the diagonal are related by $\theta\mapsto \pi-\theta$. (I could do pi+theta but I've got reasons not to.)
 
@LeakyNun Does $\exists n\forall k[n>k]$ gurentee $n$ is a maximal element for partial ordering > ?
 
is $>$ anti-symmetric?
 
2:15 AM
So for $w=0$ you get the same pure point spectrum twice, but with linearly independent eigenvectors.
 
@LeakyNun yes, cause partial orderings must be antisymmetric
 
Second, regardless of the value of $w$ one has that $H$ is invariant if you do $\theta\mapsto\pi-\theta$ and then conjugate by $\sigma_x$
 
@Leaky: What's your definition of symmetry/anti-symmetry?
 
time to put the small person to sleep
er... tuck her into bed
 
Night, @Xander.
 
2:16 AM
g'night
 
@Secret I'm more concerned that $n>n$ is false
 
Small persons go to bed at 6 PM? That seems awfully early.
That's right for anti-symmetry, @Leaky.
What's the definition?
 
So the operator $P\sigma_x$ commutes with $H$ where $Pf(x)=f(\pi-x)$
 
@LeakyNun That is guaranteed by reflexivity
 
resigns
 
2:18 AM
And then I'm happy because commuting operators are have the same eigenbasis, yay
 
@Secret one would use $\ge$ for reflexive orderings
 
$\exists n\forall k[n\geq k]$ actually guarantees a unique maximal element.
 
Context:
Feb 6 at 3:39, by Akiva Weinberger
@Secret In essence, it's a quantifier-swapping sort of dealie. It replaces "there exists an infinite thingy such that for every blah…" with "for every blah there exists a finite thingy such that…"
Feb 6 at 3:39, by Akiva Weinberger
For example, compare $\exists n\forall k,n>k$ and $\forall k\exists n,n>k$
(and > should be $\geq$)
the strange thing is that $\exists n\forall k[n\geq k]$ seemed to have $n$ as a maximal element but $\forall k\exists n[n\geq k]$ does not seemed so (e.g. natural numbers fit that expression)
 
I don't find that strange
 
I don't either
 
2:22 AM
btw the latter is trivially true
 
swapping quantifiers changes the statement a lot
like continuity vs. uniform continuity
 
This is why order of quantifiers is essential ... not strange.
Too much trouble comes from formal symbols and not understanding what's going on.
 
Ah...I see. I probably misinterpret Akiva's statement as implying the swap is the same for this case
 
somehow I get these pings like 15 minutes later.
 
You're slacking, @Antonios, if you're filling in for me :) ... (joking)
I'm about to disappear again, though.
 
2:29 AM
lol same :P
gotta read some more stuff for my independent study
g'night
 
Night, kiddo.
 
is the letter mentioned pronounced as v, or fi?
I cannot find the greek alphabet...
okay, that the greek letter phi...
 
The Greek letter phi is pronounced either "fi" or "fee" :)
 
2:45 AM
never heard of the latter way...
 
@deostroll it’s the Greek way
 
2:58 AM
@Semiclassical ugh
what is it supposed to be?
I thought you weren't teaching QM this semester
 
i'm not
it's a problem my advisor gave me
 
some notation blues:
It will be cool if there is a inequality symbol that is the opposite of << and >>
to denote slightly larger and slightly smaller
 
I tend to use $\gtrsim$ for that
...or whatever I'm trying to remember
there we go
 
3:21 AM
@Semiclassical Suppose I have a functional $E(u)=\int|\nabla u|^2+hu^2$
what would you call the $\int hu^2$ part
the first part is the kinetic part
the potential part I guess?
 
sounds valid since potentials often have a quadratic dependence
(although general potentials can be a lot more complicated than that)
 
yeah, elastic potential energy I guess
or just 'elastic part'
 
@Semiclassical christ this is a diff geo thing
I'm not calling the curvature integral the elastic part :P
oh, I'll just call it the curvature term
 
isn't curvature a 2nd order differential thingy?
 
3:34 AM
@Secret the $h$ in my case is a curvature term
so I'm calling $\int hu^2$ the curvature term in the energy
 
I know i've seen that kind of functional before, so I'm a bit frustrated that I can't remember what it's called
 
3:49 AM
@0celo7 I suspect one could interpret that term rather literally as an elastic potential energy if, for instance, you took $u(x,y)$ to be the height of a surface above the xy-plane
with each part of the surface trying to go to $u=0$ in order to minimize elastic energy
for that matter, though, I think that the grad(u)^2 terms would also correspond to elastic energy, but now in regards to nearby points on the surface wanting to be at the same height
of course, for a diff geo presentation this is all irrelevant.
 
4:10 AM
Hi
let p and q be two statements then their compound statement is always F from truth table. Then we say it is “Contradiction”? I want to confirm :)
 
@Fawad yes
 
hi
anyone active right now?
 
@Fawad Are you still in 11th ?
 
@abcd 12th. Learning topics uncovered in 11th
 
Can someone tell me what is a fancy word to say that two maps that are following each other
 
4:24 AM
@Fawad you'll be appearing for any competitive exam?
 
for example $\sigma : M \rightarrow N \rightarrow Q$
 
@Abcd EAMCET and jee mains
You in 11th or 12th?
 
@Fawad 11th is just going to end.
 
CBSE ?
 
No, ISC. (ICSE)
@Fawad when are your boards beginning?
 
4:26 AM
@Abcd 28 feb
 
Ah! That's close! Best of luck!
@Fawad So you opted for PCMB?
 
MPC (PCM)
 
okay
 
5:04 AM
@EricSilva
 
sup
 
(more empty pings in response)
 
lol
 
Seems like nerd patrol is on duty. Better get outta here
 
we're the nerd gangs bro
 
5:07 AM
@Daminark says king nerd
 
no u
 
nerd gang nerd gang nerd gang (x57 more times), spent 10 $$$ on new game, amphetamine is better than cocaine, i read a paper forgot the author's name ...
kill me pls
 
bad
 
its still less cancer than Daminark trying to rap a UChicago version of It's Everyday Bro
 
Questionable
Mine was Soug content
Soug content is good content
 
5:10 AM
the source material is better
gucci gang is bad but not everyday bro bad
 
Eric did I show you "It's Souganidis bro!"?
 
no but idc
 
lil pump is harvard graduate
 
Anyway sure the source content is better but mine actually matched the flow of the song
 
man can never be bad
 
ik ppl who hung w lil pump back in hs
twas weird
 
wait, people are roasting each other in this chat?
am I dreaming?
 
thats like the general state of the chat
 
i phrased that weird lol
ik ppl who run w lil pump who i knew from hs
 
did they scream AESCHKERET in front of people's faces for random reasons
 
5:16 AM
probably south floridians are like the worst kind of people
 
@Daminark if England is my city, does that mean America is on the north of US?
 
Youtube is blocked on my computer
guess who did it
 
@BalarkaSen!!!
 
hey hey hey
 
yo yo yoyyo
I have 25 pages so far on my tesis
I am making good progress
 
5:25 AM
good to hear
 
Yeah I am happy as well
 
@Eric learning geodesics from a variational pov now from Milnor
 
that's good progress, how much time did you take @Adeek
 
2 month @SoumyoB but instense 2 month
of working 10 hours per day
 
niiiice
good shit
 
5:27 AM
holy cow
 
I read GH chapter first chapter in like 15 days
 
I'd never be able to work at your pace @Adeek
I'd go insane
and the worst thing is I'll have to do that anyway in 2-3 years because I'm already in my first year of my PhD
 
@SoumyoB I was pushed by some insane advisor. That is, I had really bad advisor who used to always discourage me and make me feel bad about myself. Then, I changed him so in order to catch up in my master's I had to work really hard
now I am working with really good person
he is also very encouraging
nice @SoumyoB
 
that's nice to hear @Adeek
so are you doing a PhD or a Master's right now?
 
Master's and then continue to PhD
I am happy I didn't jump to PhD
 
5:32 AM
good luck
 
I am wasn't very prepared for that
thanks
 
5:43 AM
@EricSilva What is the right name for the kind of manifold the path space $\Omega(M; p, q)$ of paths from $p$ to $q$ in $M$ is?
For $\gamma \in \Omega(M; p, q)$ the tangent space $T_\gamma \Omega(M; p, q)$ being the space of vector fields $X$ along $\gamma$ such that $X(p) = X(q) = 0$ (this is the vector field you variate $\gamma$ along by pushing $\gamma(t)$ along $X(\gamma(t))$)
 
@BalarkaSen a topological manifold
 
it is not though
its an infinite dimensional manifold
locally it's modeled on some infinite dimensional space. Banach? Hilbert? Frechet?
idk
 
Naming conventions in this motherfucking subject I swear to God
 
lmao
 
Can't we call the finite-dimensional ones "Euclidean" manifolds or smth?
 
5:49 AM
I think we just call finite dimensional ones "manifolds" and add adjectives to infinite dimensional dudes
"Banach manifold"
 
0_0
That's even worse
 
lol
 
It's like "manifold with boundary"
You think adding adjectives narrows it down
 
hahah
 
But like nah it generalizes it further
Geometric topologists need to get their shit together
 
5:50 AM
you know what's worse than manifold with boundary? manifold with corners
do you know what those are?
 
I mean I can guess, like a square for example, not even really smooth necessarily
 
There's actually a course offered next semester here on nonlinear funtional analysis which will cover Banach manifolds
I'm considering taking it, because it counts as an applied course for whatever reason and I have to take 2 applied courses in the master
 
@Daminark Yeah like that. Locally homeomorphic to $\Bbb R^k\times \Bbb H^\ell \times \Bbb H^{n-(\ell + k)}$
 
classifying space ?
That looks like classifying space @BalarkaSen
 
What?
 
5:53 AM
@MatheinBoulomenos amazing
 
This $\omega$ construction looks like classifying space
 
I don't see how that is related to classifying spaces at all
 
Maybe they'll talk about applications to something like, numerical PDE or whatever?
 
I am probably very tired lol
 
$\Omega$ is the path space
It is not the classifying space.
They are related.
 
5:53 AM
sorry don't mind me @BalarkaSen @MatheinBoulomenos
oh are they related ?
can you tell me more about this ?
 
No.
 
why not :S
 
@Daminark What's terrible about manifold with corners is that topologically they are the same thing as manifold with boundaries. $\{(x, y) \in \Bbb R^2 : x \geq 0, y \geq 0\}$ is homeomorphic to the upper half plane.
Corners are not topologically any different from boundaries. They are different smoothly!
 
@Mathein I will say there's a physical science requirement, and I'll be able to use mathematical logic, combinatorics, and something TBD that'll probably be basically math
@BalarkaSen fucking rip
 
Hi chat
$\epsilon$-neighborhood or $\varepsilon$-neighborhood?
 
5:57 AM
I'm too lazy for the extra 3 letters so I use $\epsilon$
 
@Daminark oh there's funny thing here, you have to take two courses that are not in the subject you're studying. You can't take "mathematical logic" for that, because that's a math course, but "mathematical logic for philosophers" is a philosophy course, so that's okay
 
have you no dignity, no sense of aesthetic @Daminark
 
$\in$-neighrborhood
 
$C \!\!\!\!\!\! - \,\,$neighborhood
 
I mean here we have logic in the philosophy department and it's rather different from that in the math department so maybe? That or lmao loopholes are the best
 
5:59 AM
mathematical logic for philosophers is a little easier, but they cover the same stuff
 
actually MS Edge isn't even letting use chatjax
 
@BalarkaSen that dudes a hilbert manifold
 
3-neighborhood, it's up to symmetry anyway
 
what is even the point
 

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