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12:00 AM
@ACuriousMind wot
 
@Majid I think we discussed that very question above and concluded we're not sure.
 
@Majid According to Arnold (Mathematical Methods of Classical Mechanics), that part is true for all $n$
But after our recent talk I'm not sure
It's been many years since I read that
 
@0celo7 As a ring, $S$ has addition and a zero. The morphism $\phi:R\to S$ defines scalar multiplication by $r\cdot s := \phi(r)s$. Thus $S$ is an $R$-module.
The multiplication is just the multiplication in $S$.
 
Oh yeah
I had that figured out
 
So why the "wot"?
 
12:03 AM
I guess I was confused because there's no field
@ACuriousMind I was confused before, figured it out, then uhh
 
@AccidentalFourierTransform sure
 
Forgot?
 
@0celo7 You know doCarmo chapter 6, right?
 
Yes
very important stuff
 
I am confused as to why we need the transpose in $S_\eta(x) = -(\bar{\nabla}_x N)^T$ in prop 2.3
Might be because I haven't slept yet
 
12:07 AM
Transpose?
Is that not the tangential component
 
Oh is it?
 
the notation is defined on p. 126
 
I thought it's the transpose of the linear transformation of $T_pM$.
lol. that explains a lot.
 
no, see, $y$ is tangent to $M$
 
Yeah, I got it.
 
12:08 AM
k
 
nabla bar doesn't live on M, it lives on bar M
 
yup
 
Tnx
So this is of course just a generalization of the fact that shape operator for surfaces in R^3 is directional derivative of the Gauss map, modulo a sign
 
yeah
that's on the bottom of the next page
 
ah, right, i just noticed
I'm going to speedread this until 6 AM. y o l o
 
12:15 AM
do exercise 11
 
@0celo7 Ok and thanks anyway
 
@0celo7 Thanks, noted.
@Phase My last syrup just went viral / that chicken sandwich put my syrup on a spiral
Have you seen the google translated It's Everyday Bro?
 
@ACuriousMind does this chat make you feel old?
 
Sorry
Not allowed to watch Everyday bro
No-one in England is allowed to, it's banned in the whole city
 
12:19 AM
@0celo7 No, just bewildered.
 
@Phase "England is my castle" - google translated Nick Crompton
You should, like, really watch this.
 
@ACuriousMind once S7E7 airs, can we discuss spoilers
@BalarkaSen do Carmo mentions minimal surfaces, but I don't think that's up your alley
 
@0celo7 yeah I am not actually super fascinated by minimal surfaces
 
@BalarkaSen I'm on the gmt superhighway because of minimal surfaces
 
is that C^0 minimal surface theory or what
 
12:29 AM
@BalarkaSen Roughly, if you take a limit of a manifold it might not be a manifold
you have these things called varifolds and currents that generalize manifolds and chains
also in the regularity theory for mean curvature flow you might have singularities so you need a GMT treatment
 
I see, interesting
 
@BalarkaSen It's a problem with any kind of variational problem where the object is a graph or whatever and can be interpreted as a manifold
 
Btw, the proof of Gaussian curvature = Riemann curvature tensor (in particular proof of Theorema Egregium) that follows from what doCarmo does is very nice
 
@BalarkaSen Except that nowhere does he prove that the curvature is invariant under isometries :)
 
@0celo7 chains as in, homological chains?
 
12:35 AM
@BalarkaSen Integration over chains
The idea is to represent manifolds as measures
Integration over chains gives a measure
 
ah. strange.
 
I don't know much more, hence why I am reading gmt
@BalarkaSen It's actually a subtle point that the Riemann curvature is "invariant" under isometries
You can sort of argue that an isometry leaves the coordinate form of the metric invariant, so the curvature should be invariant. But there's a clean abstract argument.
 
Hm. For surface I know that Gaussian curvature only depends on the first fundamental form, the metric, so in that case it's not too hard modulo the proof of that.
Which is basically fiddling with coordinates. I guess this is what you're speaking of
I don't know the abstract argument
 
Curvature appears in the Taylor series expansion of the metric, IIRC
 
12:39 AM
these two explain it
 
Reading, thanks
i see. so this is basically just knowing $f^* \nabla = \nabla$ for an isometry $f$
which, as you say, follows from fighting with the Koszul formula. This is nice.
That's a very simple proof. I always forget that $\nabla$ is related to $g$ in a unique way and I keep missing obvious facts which follows from this
 
@BalarkaSen Right. I said that's a heuristic because one has to be kind of careful with the spaces floating around
 
Yep I know you were being careful with notation there.
 
@BalarkaSen Exercise: Prove, with this method, that geodesics are carried into geodesics.
 
If $\alpha$ is a geodesic on $M$, $\nabla_{T} T = 0$ where $T$ is a small extension of the tangent field $\alpha'$ along the curve. If $f : M \to M$ is an isometry, $f$ carries $\alpha$ to $f \circ \alpha$, (a small extension of) the tangent field to which is nothing but $df(T)$.
But $\nabla_{df(T)} df(T) = df(\nabla_T T) = 0$.
So yeah, $f \circ \alpha$ is a geodesic.
 
12:52 AM
yup
 
Whoa cool, totally geodesic submanifolds are precisely the ones with $\Bbb{II}_p(x, x) = 0$ for all $p$ and $x \in T_p M$ (for any choice of normal vector that II depends on).
Peasy to prove, but still cool.
Oh damn, so now I know why Gaussian curvature of a small bit of a 2-subspace of $T_p M$ is exactly the sectional curvature of that subspace.
 
@BalarkaSen yes
 
 
1 hour later…
2:15 AM
Welcome @SierraSorongon to The hBar.
 
0
Q: Could we ever kill 2 schodinger's cats?

user6760In the following setup I'll be testing entanglement with 2 cats, namely Mew0 and Mew1 both are positioned exactly a light year away from each other. 2 identical bombs will be strapped to each cat and they will be confined to their respective boxes, you get the idea. Now things are starting to ge...

::Cat lovers protests::
 
2:42 AM
@Secret meh
there are too many cats
we can sacrifice some in the name of science
 
-_-
 
Close your mouth
a cat hair might fly in it
 
better?
 
open your eyes
an assassin could kill you better with your eyes closed
 
3:38 AM
@AHB Don't worry, I didn't have any hope in translating. I did see some equations, which gave me the hint of the problem (Was one of them green's reciprocity theorum?)
 
 
1 hour later…
4:59 AM
Should I migrate this to Physics.SE? Does it pass the "don't migrate crap" test?
0
Q: Explain me the flow of current in wire in quantum mechanics

donghoI want to know moving of electrons in wire. One direction? Or random?

 
@NickAlexeev Hi Nick. We would almost certainly close that as "too broad" or "insufficient effort".
Where you understand that "insufficient effort" actually means "don't be an idle b*****d" :-)
 
[4 weeks and still no progress on that program]
ugh, I hate bash
The f*** is stout and all those alien terms!
 
5:19 AM
question: when referring to this chat room from the outside, do we prefer to say 1) "the h Bar", 2) "The H Bar", 3) "the hbar", or 4) "the $\hbar$"? Actually, @Jim the title of this chat room is "The h Bar"
That^ would be my preference :-)
 
@Secret stout? Did you mean stdout?
@skullpatrol I say the physics chat room and provide a link
 
...informally, yes.
I like your way better, actually @JohnRennie
 
Code fragment in detail:
steps=($(python read_steps.py $1| tr -d '[],'))

echo "steps"
echo $steps
python code:
# Read_steps module
import sys
def read_steps(filename):

#Obtain information from template<num>.com
with open('template'+str(filename)+'.com','rU') as f:
line = f.readlines()

#Obtain torsion scanning information
scan = [int(i) for i in line[9].split()]
steps = str(range(scan[0]+1))
angles = [x*scan[1] for x in steps]

print steps

read_steps(sys.argv[1])
sys.exit()
If I run the python code by itself using python read_steps.py 000, it prints the following list as expected
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120]
But if I tried to run this bash script, it only prints:
steps
0
so somehow it only can register the 0th element and forgot the rest of the list (which is converted to a string
 
What does tr -d '[],' do?
 
https://stackoverflow.com/questions/26162394/convert-a-python-data-list-to-a-bash-array

It trims away the [] and the , characters so it becomes a bash array
The full code is henious because it consists of 4 sections that need to run in sequence and I have already wrote 9 modules because of that
The code fragment above is just to grab the endpoint of a forloop to submit the files
 
5:36 AM
If I do steps=($(echo [0, 1, 2, 3] | tr -d '[],')) I get the same result i.e. steps gets set to just 0
so it's obviously something in the syntax for setting the variable steps
 
I wonder if bash is thinking [ and ] are special characters?
 
This works:
administrator@test10:~$ steps=$(echo [0, 1, 2, 3] | tr -d '[],')
administrator@test10:~$ echo $steps
0 1 2 3
But note that:
administrator@test10:~$ steps=($steps)
administrator@test10:~$ echo $steps
0
So you have one set of brackets too many
 
Those extra brackets are needed to specify bash arrays if I recall the syntax for bash arrays as variable=(stuff stuff stuff)
So I am not sure if bash can step through step as if it is an array in the for loop. Let me try and see if it works...
6666
0
6666
1
6666
2
6666
3
6666
4
6666
5
6666
6
6666
7
6666
8
6666
9
6666
10
6666
11
6666
12
6666
13
6666
14
6666
15
6666
16
6666
17
6666
18
6666
19
6666
20
6666
21
6666
22
6666
23
6666
24
6666
25
6666
26
6666
27
6666
28
6666
29
6666
30
6666
31
6666
32
6666
33
6666
34
6666
35
6666
36
6666
37
6666
38
6666
39
6666
40
6666
41
6666
42
6666
43
6666
44
6666
45
6666
46
6666
47
6666
48
6666
49
6666
50
6666
51
6666
52
6666
53
6666
54
6666
55
6666
56
6666
57
6666
58
6666
59
6666
60
6666
61
6666
62
6666
63
Yes, it works!
Thanks
(NB 6666 is just a spacer to help me track the for loop during debuging)
 
@Secret press Ctrl+K before sending a message to prettify codes
why do you have to use Bash? Python by itself looks fine
 
because motherf*** qsub of PBS pro (that is where all the nightmare came from)
 
5:49 AM
alright
 
I need its afterok function to ensure program block 2 runs after program block 1 and etc.
This whole thing has 4 blocks
and I am currently still in the 1st block
The whole program works as follows:
Step 1: Generate 120 molecule orientations and sent to gaussian to calculate energies
Step 2: After all 120 files finishes and with no error, send the 3 lowest energy of them to optimise geometry
Step 3: After Step 2 is finished with no error, send the optimised geometry to frequency analysis and wavefunction stability check
Step 4: (technically a separate block) For those calculations where one of the 120 jobs failed to complete hence resulting in incomplete potential energy surface, need to use another sscript to do step 2 and step 3 for these programs
what I have done so far is I ave spent nearly 4 weeks writing the python component of step 1-4. Now I am writing the bash component to link them all up and this is where PBS hell came from
 
I'm not sure if there is something bash can do that Python can't...
 
The major trouble is the job queing software that the cluster uses: PBS pro. I don't know of any easy way to parse all 120 exit codes from each qsub job back to python thus informing it to start executing the step 2 script
Johnrennie: Btw I think I start to have some idea why the double bracket does not work: After the string [0,...,120] is obtained and then [] , removed, enclosing it with the extra paranthesis caused bash to interpret as a subshell hence returning only 0
This is what is happening before it is assigned to steps: -bash: 0: command not found
the error prevent the next elements (which are separated by space) to be read by bash
 
 
4 hours later…
10:30 AM
@AccidentalFourierTransform yeah, what's wrong with it?
It's perfectly transparent
 
10:50 AM
wibble
hows everyone on this fine friday.
 
11:02 AM
chillin u?
 
reconfiguring much misconfigured monitoring at work
which is at least, easy ;D
tho.... why these switches aren't monitored is concerning me
also allowed to sit listening to music while I do it, which is grrrrrrrrr8
 
@djsmiley2k we don't usually bother monitoring switches since they hardly every go wrong.
 
Nod, but I can't even ping this one @JohnRennie
the rest I can at least ping.
(the staff in these stores like to unplug things for no reason.... etc)
 
If you're really lucky the staff manage to connect both ends of a patch cable to the switch and cause a broadcast storm. I've seen a few of those in my time :-)
 
11:22 AM
Have you ever seen a network melt down?
 
@JohnRennie we had TALKTALK do that just last week....
 
[Philosophy]
in Mathematics, 3 mins ago, by Mats Granvik
Why is there change in the universe?
 
@JohnRennie is it not also strange that my HDD benchmarks well below expectations
81 MBs read for a 7200 rpm drive
Maybe there's something wrong with my CPU/mobo
 
11:54 AM
@0celo7 that to me, sounds about 'normal...'
Depending on how it was tested
 
12:12 PM
@djsmiley2k It's slow for an SSD
 
Anonymous
@0celo7 What book? I know that there are plenty of crap books by Indian authors. But few are very good.
 
Anonymous
For example the one by Shankar.
 
0
Q: Musical isomorphism induced by Lagrangian (in chart)

hemmlmannI seem to have run into a (I guess largely mathematical/strucural) problem with the definition of the musical isomorphism $$\flat:T\mathcal{M}^d\to T^\ast\mathcal{M}^d$$ between velocity phase space (tangent bundle) and phase space (cotangent bundle) over a d-dimensional configuration space $\mat...

To buy the community some extra time, I have temporarily locked this post, since it is currently just 2 vote short of a migration to Mathematics. Note that the Phys.SE community usually welcomes math questions relevant for physics. Is migration what we really want?...[October 30th, 2017: Unlocked.]
 
@Blue "Probability Theory" by Varadhan
@JohnRennie I said HDD
@Blue I was taking the class but there was a topics course at the same time
I'll take probability next year
 
Anonymous
12:30 PM
@0celo7 Oh. I guess there are more rigourous books which will be suitable for you. The amazon reviews do clearly indicate that the book is more suitable for review purpose than a full-fledged course.
 
Anonymous
Anyhow, I hope you will get a better book to help you out. :)
 
what
I never said it was bad
it looks really good
It's completely rigorous
I'm sad I won't be taking the class, hope the timing works out next year
 
Anonymous
You said it is a "doubtful" book
 
it's a meme
all Indians are doubtful
 
Anonymous
Heh. Everything has become a meme nowadays.
 
Anonymous
12:32 PM
:P
 
Anonymous
You're becoming like @BalarkaSen
 
that's probably not a good thing
 
Anonymous
@0celo7 I too had to drop my Machine Learning course this semester. I'm sad about that. :/ Too many stupid courses like carpentry and engineering drawing this year.
 
carpentry??????????????????????
 
gotta build shit yo
 
Anonymous
12:37 PM
@0celo7 Yeah. Carpentry and Fitting workshop. It's fun but wastes a lot of time.
 
Anonymous
Compulsory in 1st sem
 
Anonymous
Lol...I wrote worship
 
Anonymous
Perhaps they teach it so that we don't go jobless :'D
 
books are insane
by book list for this semester has 20 books
 
Anonymous
BTW the physics professor approved my project idea. I'll be working on improving effeciency of (over-the-air) wireless chargers (yay!). One of my friends joined me for the project too. Currently doing a literature search on the topic. :)
 
AHB
12:49 PM
@PrathyushPoduval Then you don't need that site for making a problem! You can make up many yourself. There are many Green's reciprocity theorem problems throughout Olympiad.
 
I think you guys might enjoy this ;)
Could you make graphine like this....
squash it to 1 atom thick? :D
 
what's the most general definition of "n-dimensional"
A manifold is easy to define as n-dimensional, but what about a more general topological space
Is a cross 1-dimensional
Feels like it should be in some sense
 
there are various notions of topological dimension
 
plz do go on
Is it the inductive dimension thing?
 
uh, yeah, or there is the covering dimension
which is defined to be the minimum ply over all the covers of the topological space, where ply of the cover iirc means the least N such that every point belongs to at most N open sets in the cover
 
1:06 PM
Hm
What would be the dimension of a cross with that definition
I think the middle of the cross would fuck it up
 
actually my definition of covering dimension is not quite right
 
Yeah it's actually like N+1
Since if you do a cover of a line, you might get points where the refinement will always leave points in 2 covers
for instance
I think if you have a cross you'll get a minimum ply of 4
So 3 "dimensions"
 
oh god my head hurts.
Blackholes storing infomation as holograms..
 
@Slereah you can demand that your thing is in R^k, for k large
Then you can use Hausdorff dimension
 
What if it can't be embedded in $R^k$
Then so much egg on your face!
Though I'm guessing there's no good definition of dimension that gives all the correct dimensions for specific cases
 
1:15 PM
If it can't be embedded in R^k, it's not very geometric
 
Long line is fairly 1-dimensional
 
@BalarkaSen Oh I forgot to say that there's a regularity theory for varifolds, i.e. Showing these abstract measures arise as volume integration over manifolds
That's really interesting to me
 
Even worse
if you drop the manifold requirement
 
@Slereah The covering dimension is the minimum N such that every open cover of the space has an open refinement with ply at most N + 1. So for the cross, I guess N = 2 at the cross point?
 
you can have a Very Long Line
 
1:18 PM
$\omega_2 \times [0,1)$
 
@BalarkaSen : Take an open cover of the lower right, upper right, lower left and upper left
I don't think you can have a refinement where the center is in less than 4 open sets
 
Uhh, I guess you are right.
So N = 3.
 
Family of long lines: $\omega_{\alpha} \times [0,1), \alpha \in \text{On}$
 
yeah
even worse I think if it has $N$ branches it will have dimension $N$
 
yeah
and this thing is of course not defined for super dumb, non 1st countable spaces i believe
 
1:21 PM
Well it would just have non-countable dimensions :p
 
$(\omega_1+1) \times [0,1)$ is not 1st countable if I recall
 
On the other hand
A cross defined as a branched manifold would be 1 dimensional, on the other hand
 
@Slereah Ugh
 
@0celo7 Ah, OK, in that case the speed is about right for an HDD.
 
@JohnRennie google says it should be 200
My write speed is 170
 
1:28 PM
@0celo7 I've never seen that sort of speed from a SATA HDD.
 
lolololololol:
unique entry
 
@JohnRennie the 170 write?
Well I'm getting that.
 
I bet you've got the disk configured for write caching
 
@JohnRennie what?
 
Try disabling write caching so you're measuring the true write speed not the write speed including the Windows cache.
 
1:41 PM
@JohnRennie I'm in class, can you try to remind me when you wake up please :)
@JohnRennie it's an SSHD btw
Not a straight HDD
Not sure how to tell if the SSD on it is working correctly
Maybe the inflated benchmarks are because they're taking advantage of it
 
@0celo7 entirely possible ...
 
@JohnRennie I took out my wifi card so now I have an extra PCI slot
Should I get another 960 and test the speeds?
Or wait for the new ones
Or a 960 Pro
 
1:56 PM
If it turns out there is something about the mobo that is slowing things own I'd be inclined to put the money towards a new mobo ...
 
@JohnRennie So...how do I tell?
I certainly don't know of another computer with an M.2
SATA sure
But not with a good mobo
I've also had problems getting my RAM speed to 3000Mhz
That might indicate mobo issues
@JohnRennie it seems my form factor only has one chipset for mobos
Maybe I should get a new case and mobo
That's a lot of money though
 
If it was me I would just enjoy using my PC and spend the money on beer, but you knew that already :-)
 
@JohnRennie I am not 21
When I am 21 I will be broke
 
:-)
 
Gotta buy Analysis books and computer parts for now
 
2:09 PM
Spend it on drugs and loose women then :-)
 
@JohnRennie Quality parental advice there.
Actually I'd be down for the drugs if it's the YAGE
 
2:29 PM
0
Q: Can you start bounty here on physics meta if your question didn't receive enough attention for example?

Erez ZrihenCan you start bounty here on physics meta if your question didn't receive enough attention for example as you can do on the other websites in the network outside meta?

 
What is the relation about 5i^ and 1/5i^ vector
Our text book has defined them to be reciprocal to each other
 
Christ, what?
Reciprocal of vectors? Are you Indian?
 
No, I am bangladeshi
@0celo7
I googled it though but couldn't find its existence. Maybe that is defined as a different name of vector type. If u guys know then Pls let me know about it. TIA
 
Anonymous
Just google "Reciprocal System of Vectors"
 
Anonymous
 
2:45 PM
Unless you're doing stuff with lattices, I don't know for what the notion of reciprocal vectors would be useful.
 
Anonymous
@ACuriousMind I learnt it during my solid state course in chem
 
Sure, Bravais lattices and so on.
 
Anonymous
Yup
 
3:00 PM
@0celo7 Ch 6.3 is too symbol pushy for me. To be honest I never really liked the look of Gauss and Codazzi equations for surfaces in R^3 either.
 
Thanks guys
 
@BalarkaSen Agreed, but they are absolutely fundamental for geometric analysis
 
Indeed? Huh
 
@BalarkaSen They are used to derive the constraint equations for general relativity
for finding curvature estimates for minimal surfaces, etc.
Chapter 7 is deep
You'll like it
 
Anonymous
3:17 PM
 
Anonymous
@JohnRennie @DawoodibnKareem In this code how are they defining a variable of Node type before defining the class Node? Is it because the compiler doesn't parse the lines one-by-one ?
 
Anonymous
Eh...JR isn't around
 
@Blue Migrate to Stack Overflow :P
 
Anonymous
I'm afraid of downvotes ;-; For those guys on SO everything seems trivial
 
@0celo7 I'll check it out.
 
3:27 PM
As long as you have enough rep, why do you care?
 
Anonymous
If JR or DK don't come around then I'll ask on SO (after an hour or so)
 
@BalarkaSen How was thee exams?
@Blue I'm sure they would come around
 
Anonymous
@PrathyushPoduval I'll get blocked after 3 (something like that) questions (with downvotes)
 
It was okay.
 
Anonymous
The SO rules are pretty strict
 
3:28 PM
@Blue #DeleteDelete
 
Anonymous
@PrathyushPoduval That trick doesn't work
 
Anonymous
They're too smart
 
Should have thought of that :P
So when are you going to start yourproject?
 
Anonymous
@PrathyushPoduval Already started
 
Anonymous
Collecting papers now
 
Anonymous
3:30 PM
I'll visit that prof next week again
 
What's the next stage after lit review?
 
Anonymous
@PrathyushPoduval experimentation, discussing with experts in the field, investigation of alternative solutions, etc
 
When are you getting time to do all this?:P
 
Anonymous
@PrathyushPoduval It'll take time. I spend atleast 7-8 months on this
 
Anonymous
Maybe even more
 
3:32 PM
Ah long term then.....
 
Anonymous
Next year I'll ask the prof to recommend me for the NIUS workshop :P
 
Anonymous
@PrathyushPoduval Yep
 
Anonymous
Good research takes time
 
@Blue Nice, that would be a very nice experience
@Blue Yes it does
 
Anonymous
Yeah. They're very very selective. They don't take more than one student per university.
 
Anonymous
3:35 PM
That's why I'll not mention it to my classmates
 
Anonymous
:P
 
Anonymous
Actually, I'll keep the project stuff a secret(from my classmates) till I complete it
 
@Blue Nice strategy :P
@Blue Acoording to your description, I don't think most would care :P
They would be too busy protesting
 
Anonymous
@PrathyushPoduval Well, yeah. They're more interested in getting a job at Google/Facebook
 
Anonymous
@PrathyushPoduval Ah, well. Not all students are like that. :P But yeah, some are cracked.
 
3:38 PM
Speaking of which, There may be another protest here tommorow. So hoping for a holiday now :P
@Blue Every place has it's own set of crackpots and it's complement
 

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