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00:02
@Semiclassical I mean take like $\sin(x^{100})/x$. That's asymptotic to $0$ as $x\to\infty$ but the derivative certainly won't be (I hope)
$Ai(x)\sim\dfrac{e^{-\frac23 z^{3/2}}}{2\sqrt{\pi}z^{1/4}}$ @0celo7
@Semiclassical I was saying maybe $q$ oscillates violently as $s\to\infty$ so the derivative might be strange
Sure, there are problematic examples like that. But here I think the exponential supression rules that out here
in noncompact PDE we have a stronger type of asymptotic called $o_1$ that means the derivative is also asymptotic
@Semiclassical well all you need is an oscillation that is wilder than the suppression, but I don't know what q looks like so that might not matter here
like $e^{-x}\sin(x^x)$
00:25
For reference, the underlying DE is $q’’(s)=sq(s)+2q(s)^3$
@Semiclassical do you have a pretty picture of a solution?
ideally superimposed with Ai(s)
00:41
Would anyone be kind enough to recommend some must-read-paper for someone study introductory quantum field theory?
I have some but not on phone. But there’s a set of slides with nice pictures I’ll link
See slides 6-9
this fluid mechanics book is so 2002
it talks about cigarettes and compact disks
@Slereah Amazon really understands my interests, but the ad is completely wrong... i.gyazo.com/ef085f0febc340e5111abb444e69f199.png
@Semiclassical I don't get it, what was [16]?
no clue either
all I'm really interested in for this purpose is the pics on slides 8,9
@Semiclassical um, does Ai --> 0?
as x goes to infinity, yes
Airy's DE has two solutions, one vanishing at infinity and the other diverging at infinity. Ai is the former.
00:52
so why not just say that q(s) ~ 0?
(I think ~ is transitive?)
er, actually I don't think ~ 0 is defined, nvm
@Semiclassical what am I looking at on slide 8?
there's two new things
yeah, he doesn't explain that well there. but I think it's equivalent to assuming $q(s)\sim c Ai(s)$ with $c\approx 1$
one is a little above 1, one a little below, one equal
so the solution is highly unstable?
I think so. but there's some subtlety that I'm not sure about
the tricky thing is that what he's using to define his solutions is not the airy asymptotics per se. rather, there's a description in terms of the so-called stokes constant which tell you how the asymptotics change as you move in the complex $s$ plane.
numerically, though, it's definitely quite sensitive to what value of $c$ I use
@Semiclassical ah the joys of the shooting method :)
yeah
for $c>1$ you get poles on the real line I think, and for $c<1$ it's got that oscillatory behavior
$c=1$ is special in that it diverges as $x\to\infty$ but not for any finite z
01:03
"I mow the lawn with a scythe and commute to work by bike. "
the insane guy who wrote this book lol
that's commitment I guess
@Semiclassical does it make sense to have $s$ be complex and look at the whole solution?
though commuting to work by bike isn't so strange
@0celo7 yeah
so you expect complex poles then for $c<1$?
hmm. good question
01:04
@Semiclassical this guy is legendary here for cutting grass with a scythe
hmm, relevant abstract: arxiv.org/abs/1410.3338
"We show that the well-known Hastings-McLeod solution to the second Painlev\'{e} equation is pole-free in the region $\text{arg }x\in[−\pi/3,\pi/3]\cup[2\pi/3,4\pi/3]$..."
that's the solution that's being studied here, to be clear
Figure 1
nice
ffs why is my computer so slow right now ugh
delete system 32
riiight
ahah
slides 4,5,6 and esp. 8
so $|c|<1$ leads to oscillatory stuff, $|c|=1$ is monotonic, and $|c|>1$ has poles on the real line
01:37
$\renewcommand{\infty}{See, Craig, you can mess with mathjax}$
rob
rob
I migrated the post below at the asker's request, but the receiving site rejected the migration. I think it'd be fine to re-open, but I don't like reversing myself without feedback. Have a look and vote. Thanks.
0
Q: Minimizing entropy generation in storing heat

Hari GantiI am working on a cogenerative PV (Photovoltaic) array. The idea is to generate electricity from the solar cells while cooling them to both increase solar conversion efficiency and extract waste heat from the array. On a good day, the cells could easily get up to 40°C, and capture some finite (le...

$\infty$
Interesting. The borked macro doesn't affect uses above the definition.
Oh darn, I can't delete that message now.
$
$\infty$
@rob pls ban Daniel for breaking the chat
@Slereah with the recent re-establishment of the Sorbonne, if a person gets a bsc/msc/phd from some affiliated lab, can they now say they got it from the Sorbonne? :p
02:39
@BalarkaSen dear god Hempel is all in the PL category
02:58
this actually seems neat
03:13
@0celo7 PL is life
@BalarkaSen if you think that, we are mathematically incompatible
I agree
if you read Mazur-Hirsch I am going to read it too btw
@BalarkaSen remind me in 10 years...
maybe I'll read it when I finish Federer
(in 10 years)
03:17
i cant fix a proof
annoyed
@BalarkaSen story of the past two weeks for me
but replace "a proof" with "GR"
physics is unfixable
u have no hope
sorry
what proof did u break
I want to learn K theory
i have curves in R^3 which are epsilon-close to being tangential to the distribution dz = xdy. i want a curve which is tangential to it
endpoint fixed
@0celo7 since when did you get interested in homotopy theoretic stuff
smoothing theory, K-theory,...
there are heavily homotopical
@BalarkaSen smoothing because I refuse to use PL without knowing it's equivalent to Diff
K theory because it's used in conformal geometry
@BalarkaSen what does that distribution look like
03:25
it looks twisty
I have no idea what $dz=xdy$ even means
dz - xdy is a 1-form on R^3
look at zero set
it vanishes on a 2-plane distribution
oh you mean the kernel
who writes that as dz = x dy?
if you say russians I will leave
03:27
lol
i was going to say Arnold
that's it
don't talk to me or my son ever again
you have a son
he's a cat
oh i see that dude
the einstein
this talk on tuesday is going to be a disaster
but! I can blame it on physics being incompatible with mathematics
03:32
lets hope there wont be a skeptic de grande do destroy your talk
@BalarkaSen I still don't know what I want to talk about
I might just go freestyle
 
1 hour later…
04:47
High command, it is true that Balarka Sen is now slightly more weird since The Incident, causing the weirdness level to only drop significantly only if the Lockdown Trio were present all at the same time. But that does not mean we don't need to be cautious. Until The Plan is completed, he and the two other members of the Trio has to be continuously monitored
The status of h bar still remains unstable and if we are not careful, the weirdness will be drained completely, making it inhospital to THEM
 
1 hour later…
05:59
@vzn this
Hey, anyone here care about quantum many-body physics?
06:32
@Slereah I was offered a job by the atomic weapons research establishment. I even went for the interview but the place was horrible. The staff seemed to be all failed academics. Presumably they were the only people desperate enough to accept a job there.
Anonymous
06:56
@JohnRennie That sounds strange, considering that it operates under the British government. Are there better private organizations which does that kind of research?
@Blue I think the vast majority of scientists disapprove of nuclear weapons and wouldn't want to work on them. I only applied for a job there out of curiosity to see what it was like. I would only have accepted the job if I had no other job offers.
Anonymous
@JohnRennie "vast majority of scientists disapprove of nuclear weapons and wouldn't want to work on them"....that's nice to hear :P
I was offered the job back in the early 1980s but even then it was clear that the UK was winding down its work on nuclear weapons. I think the work they do now is just maintenance rather than designing anything new, and I doubt it's very exciting.
What we need is to stir up another war
Isn't that what Trump is attempting to do in Korea?
07:03
Unclear
Anonymous
I see. As for me, I'm totally fine with doing weapons research as long as there is no mass manufacturing endeavour. But then again it is even better for world peace if such research is minimized.
But once we have a war, the nuclear research and engineering would be hip again
Anonymous
War isn't as cool as it sounds.
@Blue no manufacturing, no money pal
I'm not sure how much scope there is for research in nuclear weapons. I'd have guessed the area was pretty thoroughly understood by now.
07:05
hm
i guess
the boiz in the cold war finished doing the good stuff
Another cool game from ncase about why people do/don't trust each other, based on game theory
how can someone dislike the moon this much
07:32
@JohnRennie too bad
Might be fun designing nukes
"This is my new bomb, it kills everyone everywhere"
08:20
I would rather having people start making bombs and kill all of us humans. Because humans are so boring and a waste of universe resources
Well you know what I say, lead by example
actually, I am not sure if fusion bombs makes a cleaner kill than fission bombs
@Secret fusion bombs use fission to start the hydrogen fusion, so they are just as dirty as fission bombs
right
hmm guess an antimatter bomb is needed to prevent radioactive fallout, but antimatter is super hard to produce so whatever...
@JohnRennie I've heard of some fissionless designs
Though I don't think they were ever tried
Did you ever wonder if your toothpaste was used for evil, @JohnRennie
08:32
@Slereah personal care products have limited applicability as weapons of mass destruction
Though didn't the US attempt to assassinate Castro by putting poison in shampoo or something similar?
@Secret antimatter:matter fusion is a hopelessly messy process that spits multiple hadrons out in all directions. While it doesn't produce the radioactive fission products that U235 creates it will induce secondary radioactivity in the matter around it.
I think the US came up with like 50 plans to assassinate Castro
Antimatter is also not something that's very energy efficient to produce
All this time he was producing GDP
Anonymous
08:55
Visual Studio's random number generator seems to be buggy! Every time I run the program afresh (after re-building it), it gives the same output. Only if I put the code in a loop, it gives new results each time. (I just used rand())
Maybe you need to generate a seed first
then just put like seed = md5(timestamp)
Anonymous
I don't know what that is. Checking...
Anonymous
@JohnRennie Do you have idea about this thing? ^
Anonymous
3 mins ago, by Blue
Visual Studio's random number generator seems to be buggy! Every time I run the program afresh (after re-building it), it gives the same output. Only if I put the code in a loop, it gives new results each time. (I just used rand())
Also what do you mean by "visual studio"
What language are you running on visual studio
Anonymous
09:01
Visual Studio doesn't have gcc I think. It uses some in-built C libraries (I think)
Anonymous
I haven't tried it using the gcc compiler...got to check
"The rand function returns a pseudorandom integer in the range 0 to RAND_MAX. Use the srand function to seed the pseudorandom-number generator before calling rand."
Did you use srand
srand( (unsigned)time( NULL ) );
is advised
Anonymous
I was just reading about srand()
Anonymous
Trying
Anonymous
"rand() function is used in C to generate random numbers. If we generate a sequence of random number with rand() function, it will create the same sequence again and again every time program runs. Say if we are generating 5 random numbers in C with the help of rand() in a loop, then every time we compile and run the program our output must be the same sequence of numbers."
Anonymous
09:04
Aaaaaahhh!
Anonymous
That's the culprit
Anonymous
Lol
You need to use srand to set a random seed
Using the timestamp directly isn't necessarily advised if you're doing secure stuff btw :p
Anonymous
Awesome. This works great. Learnt something new today :P
Anonymous
09:11
@Slereah Yeah, I'll keep that in mind, hehe XD
Otherwise knowing at what time a number was generated allows you to narrow down what number that could be
Anonymous
I think there some third-party truly random number generator libraries for C, online (I doubt how much truly random they are...but anyway :P)
You can generate some fairly random numbers if you're using hardware stuff
like if you're measuring voltage on the CPU and only keeping the least significant digits
Anonymous
Yup, that's one of the useful ways to generate random numbers :)
Anonymous
And then you have the superposed states of qubits :P QC guys would like that method
09:17
x86 processors have TSTR—Thermal Sensor Thermometer Read Register
You can just measure the temperature
Let's see to how many digits
Anonymous
I heard there's some serious research in this area (in cryptology departments...which I don't know much about...but it sounds interesting)
Anonymous
@Slereah Yeah, temperature, light intensity, all those stuff. I once made one using a Arduino XD
Anonymous
My light sensor was pretty pathetic though
Apparently it's just degrees directly
Anonymous
(cheap arduino stuff)
09:18
Not very good for randomness
on 8 bits signed
just in case your CPU freezes
0
Q: Modified question on hold won't reopen

SafronI posted this question (previously called "Lagrangian of two pendulums tied together") five days ago, whereafter it was soon closed as off-topic. The reason for this was understandable: it looked as if I was asking for the solution of some exercise. As I realized my mistake, I radically rewrote ...

09:38
@Slereah I really like the aesthetics of this image
Grim Reaper grinning at you from the distant from a picture frame littered with SHUTTERSTOCK watermarks
A grim foreshadowing of the future!
Anonymous
@JohnRennie There's a certain program: paste.ofcode.org/uCVGfy7YGwELcyhy2jW5sE which works fine on VS. But when I execute if from cmd using gcc, it gives 100s of errors saying that there are null characters in the code. I'm not sure how to deal with this
10:01
is this an on-topic chat or a casual chat?
Anonymous
@DBinJP casual....mostly off-topic chat :P But you're free to ask physics questions...
I was going to ask how to reset motivation and confidence when you've become mentally exhausted.
Anonymous
Well, you can ask that.
... 'kay.
how to reset motivation and confidence when you've become mentally exhausted?
Amphetamines.
10:07
what, like, advil?
please
It's the Paul Erdös approved way
methamphetamine > amphetamine
Also take a vacation if you can I guess
temporarily go on a different intellectual adventure/exercise than the one that mentally exhausted you
thats how i regain motivation
in other words do a productive procrastination
10:14
yeah, problem is i seem to have ruined my life doing that
jumping around different fields, not mastering a single one
the fix is to not jump around vastly unrelated fields i think
i have this problem of losing interest in whatever i'm supposed to be doing
stay on related disciplines so your random walk is limited to a specific thing at least superificially
i have tried to do that ...
what do you work on?
10:17
medical physics
been learning ubuntu linux, data science, statistics ...
tried R but it's too austistic even for me
returned to MATLAB
mm i see. thats something i hardly have any expertise on so i cant suggest anything specific. maybe the others here can though
i think my main problem is my research advisors are neither researching nor advising
Anonymous
@DBinJP What's the problem with R ? I mean the things you mentioned aren't very unrelated...statistics...data science...etc
Anonymous
Those things are useful even in experimental physics
i think i didn't have time to learn a new language (i.e. new commands), and R was too picky about data frames and how data is structure
d
matlab is pretty simple -- is it an array? make it one, and you can proceed
R is like, you have to name the rows and columns and which type of array and use different commands for each of those things ... ...
too many layers blocking me from actually using the data
10:22
Just use C if you don't like that :p
You can just use arrays with anything!
and the documentation -- MATLAB is like, "here's the command, here's an example, very clear"; R made documentation about documentation just for the sake of having it, like latex
so i spent too much time reading documentation without actually learning how to do what i was wanting to do
Anonymous
There are tons of good lecture series on R on YouTube. I'm learning it currently. Doesn't look too out-of-the-world. But then I'm going at a very slow pace.
yeah, 'very slow' -- i ran out of time for that
i needed to clean up messy data and start using it
not start from scratch
but i do like hadley's tidydata ideas
Anonymous
@DBinJP Well, you're running out of time...for "what"?
to do my research and publish a paper and graduate
what i'm trying to do now, except i'm burnt out
Anonymous
10:26
Seems like you're not enjoying your research ?
i'm not
strikes me as a waste of time
Anonymous
Hmm. I see now
@Slereah Isn't crack better?
Cocaine is for businessmen
Anonymous
Maybe someone more experienced can give you suggestions for that. I'm not the right person
Anonymous
10:28
Good luck though
thanks
hola?
I don't do languages.
ola = ?
10:31
probably
why's leo always doin' drugs man
I wonder how Erdos on amphetamines acted like
every movie leo's always upset about something
Imagine him just rambling on number theory
10:33
> Erdős never married and had no children.
you don't say ...
dang, this dude's like the St. Francis of math
@Slereah The good thing about Amphetamine (compared to crack or cocaine) is its lengthier high time
It's better suited for scientific work
Any thoughts on this meta question will be great and helpful: it seems that the professor of the class does not think he could answer a similar question; physics.meta.stackexchange.com/questions/10367/…
@ConstantineBlack i've always seen this website say it's not for homework help
'this' = stackexchange
but i think i've also seen homework solutions posted here
won't it just be downvoted or closed if off-topic?
Erdos is quite famous
Among the math crowd
i can see why
10:40
He's the Kevin Bacon of math
kinda forgot kevin bacon ...
I'm asking on meta because I don't think it's a homework question- if it is valid to be posted then the question is about the possible hypothesis or whatever that would make the second part of the problem correctly solvable.
That' s because the given relation cannot give right results for the second part for both t=0 and t=infinity. Or it seems so to me.
I think a 15-20mg dose of amphetamine should be prescribed to all math or physics students. especially before their exams:
>ego inflation
>increased libido
Might be a joke about Feynman here
:)
analysis enhancement, focus enhancement, memory enhancement, motivation enhancement, thought acceleration, thought organization.....these are gold to those trying to solve difficult problems
10:46
who cares about solving difficult problems
its all bullshit
@BalarkaSen Those who have exams or are doing research
you wouldn't say that if you were on drugs
aka bullshit
@Slereah good drugs are the hallucinogenics
What's the point of these exercises, anyway?
nvm
@BalarkaSen good hallucinogenics are good
Bad hallucinogenics are bad
10:49
what i mean is that i think there's not enough time spent teaching how to use computers
science is just a device humans developed to keep themselves from being bored
Did you ever read the side effects of nutmeg
and too much time spent solving problems by hand
so i'm glad to hear the problem must be solved with matlab rather than by hand
its all just a big bullshit
@BalarkaSen i'd say that's only partiall ytrue
10:50
"Nutmeg intoxication can vary greatly from person to person, but is often associated with side effects such as excitedness, anxiety, confusion, headaches, nausea, dizziness, dry mouth, redness in eyes, and amnesia.[21][24] Nutmeg poisoning is also reported to induce hallucinogenic effects, such as visual distortions and paranoia.[24]"
TV is more literally such a device these days ...
IIRC one effect described was "vision of demonic animals"
which sounds mildly worrying
@Slereah Sounds like my thing
nutmeg::humans as catnip::cats?
No, it's not the fun kind of high
10:51
@DBinJP yeah but you cant pretend you're doing IMPORTANT STUFF when watching TV
I can
It is supposed to be a computational physics class... but it's pretty basic and that's why I don't know if I must make some hypothesis to solve the second part or not; the professor thinks he cannot answer that.
can you get funding for your TV watching time?
@BalarkaSen good point, but it seems the people who watch tv don't care about that when they're doing it
@BalarkaSen I mean, it's like turbo mode. You shouldn't normally use it too much but sometimes it really helps
10:52
get funding from the authorities and then ill believe you
@ConstantineBlack well, yeah, you have to connect the dots to see what the math should be when the box partitions start with different amounts
@Slereah bad trips are the best kind of trips
@BalarkaSen feel free to try
Although don't buy all the nutmeg at once, nobody's gonna believe you're baking 2000 pies
Well, yeah... but I begin from where? From the given relation? From more fundamental assumptions? This is not a statistical physics class, the given relation is just given and does not stated from where it came as a result.
oh.
@ConstantineBlack The question is not clearly asked, I think, but I think you may just assume it to be starting from the time there were that many particles from the first part of the question.
e.g. t = 3 minutes instead of t = 0
but i would state this reasoning
*the reasoning for this assumption
or t = 3 seconds rather (shrug)
(i think it wouldn't stay a vacuum for minutes ...)
goodnight
11:01
I have no idea what these nanoparticles are and why the partition is such. It's just an exercise to be solved in matlab so I'd like to ask on the main site if there is a proper way, from the given relation, to understand how to model the second part of the problem or if even matlab can somehow find a solution- solving a system perhaps for both partition.
@DBinJP Yes I also thought that; but it's just an assumption I make and it bit of frustrates that the professor cannot state if I must assume anything or not.
11:11
Hey @Blue you there?
Anonymous
Yeah, but will have to leave soon
@Blue You have a chegg account right? Do you mind checking out an answer for me?
Anonymous
Sorry, I disabled it a month back...
Anonymous
Not paying anymore
@Slereah nutmeg is so good though
11:15
@Blue Oh okay
thanks
@Mithrandir24601 will actually bake 2000 pies
1
Q: About the validity of a question regarding the modeling of a system for a matlab problem

Constantine BlackI'm posting this on meta to ask if it is OK to post a specific question. In more detail: I've been given a problem that needs to be solved on matlab. The problem states that a box of nano particles is given and that at $t=0 $ all the particles are confined in one part of the box and that part is...

11:34
@Blue I bet you've written it using unicode! :-)
@Blue Unicode text represents every character by two bytes, and for ascii characters the upper byte is always zero so for would be \x0 f \x0 o \x0 r. If you asked gcc to compile source code written in unicode it will have a fit about all those \x0 characters.
11:49
I will just change the relationship given so that it satisfies the appropriate physical conditions.
Anonymous
@JohnRennie Uh oh. Any way to interconvert?
Anonymous
gcc isn't unicode compatible...weird!
@JohnRennie Depends on the encoding!
There's dozens of unicode encodings
@Blue Linux doesn't like unicode. It prefers the UTF encoding.
UTF-8 is just 8 bits but can widen if you have the appropriate codepoint as the first nibble
Up to 64 bits
Anonymous
11:57
I see. Hmm. Do I have to type the whole thing again, then? :P (to run it using gcc)
@Blue easy :-)
Open the source file and choose File/Save as
To the right of the Save button is a little arrow. Click that and choose "Save with encoding" and set the encoding to Western European codepage 1252.
That will convert it back to ASCII.

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