The h Bar

Sir Cumference

2:18 AM

@BernardoMeurer I have to ask, if you have no interest in physics, what brought you to this chat?

0celo7

2:31 AM

@SirCumference me

Argon

2:55 AM

My prof. wrote that for degenerate perturbations, $$E^2_n = \sum_{k^\circ \notin D}\frac{|\langle n^\circ {'}|H_1|k^\circ\rangle|^2}{E_n^\circ - E_k^\circ}$$ where $H_1$ is perturbation Hamiltonian, and D is (apparently) the set of $|n^\circ{'}\rangle$ that diagonal $H$ and are formed from linear combinations of the degenerate states.

Is my understanding of $D$ correct? Moreover, how am I to interpret $k^\circ \notin D$?

DanielSank

Hi @0celo7.

Secret

3:17 AM

rspa.royalsocietypublishing.org/content/473/2207/20160887

Hmm, any of you GR people aware of such instability?

Mozibur Ullah

3:37 AM

That article is behind a paywall, a preprint was posted on the Arxiv in 2014 - it looks interesting.

Qmechanic

7:44 AM

3

Q: What are the steps to identify a dark matter candidate?

By looking at the Lagrangian of a simple particle physics model, how do people identify the dark matter (DM) candidates, if any? One of the criteria is to check whether the electric charge of the suspected candidate zero. But that is not sufficient. What are the steps to identify a DM candidat...

Too broad? Unclear what is asked?

Slereah

9:30 AM

mornin

Tim Wilson - Booty Song

►

CooperCape

9:59 AM

Wouldn't recommend stapling yourself - it sounds fun but it's not particularly worth it.

Slereah

I'd recommend stapling your mouth :V

CooperCape

Nah miss me with that.

Anonymous

12:02 PM

@CooperCape You there? This color edition of Axler's textbook is a treat to the eye. Since you were learning LA I thought you might find it useful.

Anonymous

Also, the last few chapters include some material that is not in Artin

CooperCape

@Blue I am now - I'll check it out (kinda bored anyways)... thanks!

oh nice

Anonymous

I have a strange fascination for colored textbooks :D

Anonymous

All textbooks should be colored, actually :P

CooperCape

nothing like a pretty picture to spice things up

actually my A level maths books have nice colours

integration's a nice cyan.

Anonymous

12:14 PM

True. Even the typography is neat and clean.

CooperCape

oooh it starts on vector spaces - neat.

that's something I know nothin' about

Anonymous

@CooperCape Hehe. Get to uni and you'll find that all graduate textbooks look like 100 year old research papers bounded in form of a book. :P

Anonymous

@CooperCape Ah, you should learn it soon :)

CooperCape

@Blue Awww those kind of things are kinda disengaging in a way...

Maybe I'll finally know what people chattin about when they write $C^n$ all over the place?

Prathyush Poduval

I don’t think this is the right book for it.....

CooperCape

12:18 PM

Rip

I saw a C and was like huh

I'ma stay away from analysis

far away

Prathyush Poduval

@Blue does this have different content from the black and white one?

I find the b&w much more easier to read, it has less distractions

Anonymous

Oh, just $\mathbb{C}^n$ means: $z=(z_1,z_2,....,z_n)$ where each of $z_i$ are complex. $z\in \mathbb{C}^{n}$

Anonymous

There's another C^n which you'll learn in complex analysis

Prathyush Poduval

Wait no

Slereah

i think you mean $\mathbb C^n$ :p

CooperCape

12:20 PM

Uh huuuh

Prathyush Poduval

@Blue It means n times differentiablevright?

Anonymous

@PrathyushPoduval That's the one is complex analysis. Yeah

Anonymous

Different books use different notations

Prathyush Poduval

Oh okay, didn’t see the following message

Slereah

$C^n$ is in all analysis, even

Anonymous

12:23 PM

@Slereah True :)

CooperCape

Analysis looks hard and icky from from my perspective...

(that is the perspective of one who knows nothing of it...)

Anonymous

@PrathyushPoduval So you're busy tonight, no? I was learning the inner product and bilinear form today. (I need to understand the maximization properly. I did see your message) Let's meet on Tuesday then? (Or are you free tonight?)

Prathyush Poduval

@CooperCape That’s what even I thought, buts It’s quite wonderful once you go into it

Anonymous

@CooperCape Everything is hard before it's easy

Anonymous

:P

CooperCape

12:25 PM

@Blue so motivational ::sobs::

Anonymous

But then, I never heard anyone say analysis is easy....

CooperCape

sounds cooll

Anonymous

XD

Prathyush Poduval

@Blue I’m going to ernakulam right now, will be back by Monday night

Till where are you doing it?

Anonymous

@PrathyushPoduval Enjoy. I will try to understand the maximization problem properly today. I'm doing chapters 6/7 from Axler and Bilinear forms from Artin

Anonymous

12:26 PM

Artin also has a small section on maximization problems...gotta read it

Prathyush Poduval

Okay. I’ll go through artic and see that section then

Anonymous

Okay, see you on Monday/Tuesday!

CooperCape

Here's a weird one... How is my total rep 1131 but my year rep 1166

I swear that doesn't work.

Mr. Xcoder

@CooperCape You have 1181...

CooperCape

That would do it... Probs hasn't updated...

Slereah

1:06 PM

Finite Simple Group (of Order Two)

►

classic tunes

Loong

It's already dark again. And before the sun comes back tomorrow, it will be −8 °C.

Anonymous

1:23 PM

What does $P(\Bbb R)$ mean?

Anonymous

Slereah

1:45 PM

Power set?

No I guess not

Anonymous

It should be something such that $p,q\in P(\Bbb R)$

Anonymous

I think

Anonymous

Ah. $p,q$ are functions

Anonymous

$P(\Bbb R)$ is a function space I think

Anonymous

Integrable on $[0,\infty)$ (?)

Anonymous

1:53 PM

Anonymous

Heh, jokes in a maths book. Nice

Prathyush Poduval

Polynomials with real coefficients is what I think it is

@Blue yeah it’s something like that. Sheldon gives the definitions in the beginning of a chapter and forgets about it

Anonymous

@PrathyushPoduval Ah, okay

Anonymous

P is probably for polynomials

Prathyush Poduval

Yeah

Anonymous

1:59 PM

Are you on the way?

Anonymous

To ernakulam

Prathyush Poduval

Yeah, but I am free now

I tried sleeping but I couldn’t:(

Anonymous

Hehe. In car or train ?

Prathyush Poduval

Train, no way I would agree by car. It's a bloody 9 hour drive :P

I found the successor to surely your joking, im downloading that noe

Anonymous

@PrathyushPoduval Oh, Feynman's? I saw that book once

Prathyush Poduval

2:02 PM

Yeah, quite a wonderful book that is

Anonymous

True :D

Prathyush Poduval

The range keeps on changing very fast. One moment I have 4g and the next I have no service

Anonymous

Use 3g instead

Prathyush Poduval

They need to introduce WiFi on trains soon

Anonymous

3g is more stable

Prathyush Poduval

2:11 PM

@Blue it uses the fastest available option

Anonymous

@PrathyushPoduval There are WiFi hotspots on some trains

Prathyush Poduval

Changes automatically

Anonymous

@PrathyushPoduval Go to Settings and Select 3G only

Prathyush Poduval

@Blue which ones?

Anonymous

Rajdhani Express has WiFi I think

Anonymous

2:12 PM

And some more

Anonymous

But they need to increase, true

Prathyush Poduval

Yeah

How do I get chatjax on mobile browsers?

Anonymous

@PrathyushPoduval math.ucla.edu/~robjohn/math/mathjax.html

Anonymous

Scroll down

Anonymous

For Troublesome Mobile Browsers

If your browser cannot add bookmarks using drag-and-drop or a contextual
menu, add a bookmark as instructed below. Execute this bookmark from the
chat window to start ChatJax.

1. Copy the text from the box below.
2. Create a bookmark to this (or any) page.
3. Replace the contents of the bookmark URL with the copied text.
4. Edit the bookmark title if you wish.

Prathyush Poduval

2:18 PM

I need to find out how to change the bookmark url.....

Ah it's done, thanks

Anonymous

Go to the Bookmarks' manager

Anonymous

Great!

Prathyush Poduval

The book has finished downloading, I'm going to read it now

Anonymous

Cool

Anonymous

Give review later

Prathyush Poduval

2:22 PM

Damnit

The one I downloaded has a whole 100 pages missing :(

Anonymous

Read the rest XD

CooperCape

Why is this my most upvoted answer. Like seriously it's kinda bad... Also the one below it is better anyways...

VenkiPhy6

Hi! Does anyone know of any source that discusses network analysis of a circuit with just Maxwell's equations without using any of the circuit theory ideas(like Kirchoff's laws, Norton/Thevenin's theorem)? Basically I am trying to convince people of the importance of the lumped matter abstraction and feel like showing the horror of using Maxwell's equations for network analysis can be useful...

Anonymous

9

Q: How can KVL & KCL be derived from Maxwell equations?

How can KVL (Kirchhoff's Voltage Law) & KCL (Kirchhoff's Current law) be derived from Maxwell equations in lumped circuits? (Lumped network: if $d$ is the largest dimension of the network and $\lambda$ is the wavelength of the signal, a lumped network satisfies the condition $d \ll \lambda$ where...

electromagnetism electric-circuits maxwell-equations

Slereah

2:37 PM

@VenkiPhy6 also remember that the magnetization and polarization vector in Maxwell stem from the Dirac equation :p

Via the Gordon decomposition

Really using Maxwell equations for circuits isn't a good idea unless you're dealing with like millions of volts

Otherwise you have to deal with the shape of circuits

A circuit is gonna generate magnetic fields all over since it's just a loop

But who cares

Prathyush Poduval

2:53 PM

@Blue I came across this competetions tessellate.cmi.ac.in/#stems

You taking it?

It might be a good one, since it's by cmi students

Anonymous

Nice. I'll see the papers later. But I'm not really interested at the moment

Rick

Has anyone given it before?

How's it like?

Prathyush Poduval

It's a first time they're holding it I think

Anonymous

@Rick It seems like the first time they're conducting

Rick

Oh..ok

So it's the syllabus is similar to the Olympiads

cut that extra it's :P

Kiarash

3:02 PM

Hey guys. Has anyone here read the "QUANTUM GEOMETRY OF BOSONIC STRINGS" paper by Polyakov? I don't understand some points of it

Rick

@PrathyushPoduval Are you giving it?

@Blue what about you?

Anonymous

@Rick No. I'm not interested in Science/Math competitions at the moment

user228700

3:49 PM

Hello, everyone :-)

Anonymous

Halo

user228700

@Blue What are you up to?

Mithrandir24601

@Kaumudi.H ni hao!

user228700

When do your holidays end?

user228700

@Mithrandir24601 :-) I have coffee tonight!!

Anonymous

3:53 PM

@Kaumudi.H Doing some project work. What's your next exam? :)

user228700

@Blue Nice!

user228700

My next paper is Basics of Electrical Engineering.

Mithrandir24601

@Kaumudi.H Haha! ☕ I'm currently drinking some jasmine dragon pearl tea, which is easily the best jasmine tea I've ever had (not really surprising considering I got it in China) :)

Anonymous

Heh. Circuits and stuff :D

Anonymous

@Mithrandir24601 Wut

user228700

3:54 PM

@Mithrandir24601 Jasmine Dragon Pearl Tea?!?!

Anonymous

"Jasmine Dragon Pearl Tea"

Anonymous

LOL

user228700

@Blue Yep! Electrical Circuits, Magnetic Circuits, Transformers, DC/AC Motors & Generators, AC 3 Phase Distribution Systems etc.

user228700

Much fun!

Anonymous

amazon.in/Jasmine-Pearl-Green-Tea-50/dp/…

Anonymous

3:56 PM

So you just add a dragon to that. I see

user228700

Wow, I see.

user228700

Well, I don't like tea! Coffee FTW!

Anonymous

Conc. Hot Chocolate> Coffee > Tea :D

user228700

It is easier to stay up during the Project For Awesome, especially when coffee is at my disposal, because some of my favorite creators are hosting the livestream!

user228700

@Blue Well, hot chocolate is more expensive to make! :-P I is broke.

Mithrandir24601

3:58 PM

@Kaumudi.H @Blue evidently neither of you have ever had a truly delicious cup of tea :P

user228700

:-P Right.

user228700

Over the past 23 hours, over 1.6 million dollars has been raised!

Anonymous

Is he playing Holi?

Anonymous

@Kaumudi.H Congrats!

Anonymous

3:59 PM

(To the project :P)

Anonymous

1.6 million is a lot

Anonymous

Nice

user228700

@Blue Lol, no, his children covered his face with sharpie doodles when we hit a milestone. 1.4 million, I think.

Anonymous

@Kaumudi.H Hehehe

Anonymous

@Mithrandir24601 Maybe. I don't think I had more than 10-15 cups of tea in my lifetime :)

Mithrandir24601

4:03 PM

@Blue ... I'm only on my 2nd today - I'll make another in about half an hour, then a 4th before going to bed - I generally average between 3 and 6 per day :P I also have hot chocolate once, sometimes twice in a week and I despise the vast majority of coffee

user228700

Oh, my, that's far too many cups of tea!

Anonymous

@Mithrandir24601 You're like my father, lol. He has 6-7 cups of tea a day I think

Mithrandir24601

If you ever see a talk recorded where I'm in the audience (or even where I'm doing the speaking...) I'll be the person drinking the tea

Anonymous

There must be something called Tea addiction :D

user228700

> even where I'm doing the speaking...

user228700

4:05 PM

Really?!

Anonymous

lolol

Mithrandir24601

@Blue Nonsense! Addicted to tea! Simply absurd!

Anonymous

@Kaumudi.H "sip..sip....erm, where was I?"

user228700

Where's John tonight?

Mithrandir24601

@Kaumudi.H Yep - I'm dead serious about this

user228700

4:06 PM

Ah, he's probably attending the SF meeting tonight!

user228700

@Blue x'D

user228700

@Mithrandir24601 Wow.

Prathyush Poduval

@Rick yes I am, I think it'll be good practice for me

Mithrandir24601

@Kaumudi.H I mean, most people have a glass of water sitting there when they're giving a talk about something - on the two(?) times I've actually given a talk, I've just had tea instead of water

user228700

Nice! :-)

Mithrandir24601

4:08 PM

Oh wait, plus that time I did a talk at school :P

user228700

Wait, even then?!

Rick

@PrathyushPoduval I'm thinking of doing so

Mithrandir24601

@Kaumudi.H As in, I was just about to start my PhD, having just done an MSc in gravity etc. and only after a few months of the announcement of the discovery of gravitational waves, so I went into my old school for an afternoon and gave a talk to the astronomical society about gravitational waves :)

Rick

They say people from 8th to 12th will give the same paper, and not to worry about the syllabus on the webpage. Does that mean normal high school/JEE concepts will be enough or we'll have to study other stuff like Number Theory?

Sir Cumference

Morning

Mithrandir24601

4:11 PM

@SirCumference ni hao!

Prathyush Poduval

@Rick maths will be more Olympiad based, since it's from cmi. I know as much as you do now :p

Anonymous

@Mithrandir24601 What does MSc in gravity involve? GR stuff? QG?

Anonymous

BTW it must be nice to go back to your old school to give a talk :)

Prathyush Poduval

@Mithrandir24601 are you in china right now?

Anonymous

He's back in UK

Prathyush Poduval

4:15 PM

Nice, what we're you doing there then?

Anonymous

Some conference

Mithrandir24601

@Blue It was gravity, particles and fields, so GR, more GR, black holes, QFT, cosmology, differential geometry, quantum information and a dissertation (I did mine on weak measurements)

@PrathyushPoduval I came back on Wednesday from a conference on 'trapped quantum systems', so things like quantum devices based on trapped ions, cold atoms and photonics as well as a bit on (charge-)parity-time symmetry

0celo7

@Blue that image you

Posted is complete nonsense

P(R) means the power set, somehow those are functions (not true), and that integral certainly doesn’t make sense for all functions

Prathyush Poduval

@0celo7 no it ain't

Notation depend on how you define them, And it has been defined in the book as a vector space of polynomials

0celo7

Ok, then it’s fine

Slereah

4:36 PM

Some progress

The hard part will be putting it in a thing

The hardware store didn't really have a box to put electronics in

Prathyush Poduval

@Slereah what's that?

Slereah

Christmas present thing

It will blink christmas colors and display christmassy sentiments

And play christmas music

And also it's a arduino inside so u can just reuse it

Prathyush Poduval

What's the screen for?

Witty quotes?

Slereah

to say MERRY CHRISTMAS

And other such things

Mithrandir24601

@Slereah So... Non-witty quotes then?

Slereah

4:41 PM

Well I mean

you could, yes

but tis not the season

Prathyush Poduval

Well, its a waste displaying only merry Christmas.......

Add some made up quotes of Santa

Slereah

Eh who cares

Prathyush Poduval

And newtiom

Slereah

It's a cheap chinese LCD

0celo7

Einstein quotes

Balarka Sen

4:46 PM

so

what movies are on your Christmas list

Prathyush Poduval

I wanted to watch scanners, didn't get the time yet

Balarka Sen

not a christmas movie, but a very good one

Prathyush Poduval

Die hard then

Balarka Sen

+1

classic choice

Prathyush Poduval

Yeah

His swag never gets old

What bout you?

Balarka Sen

4:51 PM

dunno

's why i asked

Prathyush Poduval

The doctor who Christmas special is also on my list, though not a movie

I've been waiting for it since june

Balarka Sen

i don't watch doctor who. should i?

Prathyush Poduval

Yeah it's quite good

Initially, you may find it a bit cringy

Watch Rick and Morty too while you're at it

Balarka Sen

To be fair, you need a high IQ to recognize fellow Rick and Mortisans

I know all the inside jokes. There is no other reason for me to watch it :p

Anonymous

@0celo7 It's from Axler

Balarka Sen

4:56 PM

I know theoretical physics

Prathyush Poduval

IQ 10000+

Right off the charts

Slereah

Balarka Sen

it's OVER 9000

Bernardo Meurer

Does anyone here know how to use awk?

I need guidance

@dmckee @JohnRennie

Slereah

Well I've used it

I wouldn't go as far as saying I know how to use it

Bernardo Meurer

5:02 PM

Yeah

I'm trying to do something with sed but I think I've reached its limits

Slereah

what are you trying to do

dmckee

5:20 PM

@BernardoMeurer It's been a while since I coded in awk, but it is not a hard little language.

0celo7

@Blue linear algebra is the worst math

Slereah

what about set theory

dmckee

Here's some evidence that it can be made to sit up and do tricks:

7

A: Build an ASCII chart of the most commonly used words in a given text

Gawk -- 336 (originally 507) characters (after fixing the output formatting; fixing the contractions thing; tweaking; tweaking again; removing a wholly unnecessary sorting step; tweaking yet again; and again (oops this one broke the formatting); tweak some more; taking up Matt's challenge I desp...

(from before Programming Puzzles & Code Golf, when a few such questions were being allowed on Stack Overflow.

DanielSank

sigh

Slereah

Harvey Birdman - Sigh

►

DanielSank

5:30 PM

uhhh, ok

?

Bernardo Meurer

it has a history file that looks like this

@Slereah @dmckee I'm trying to get the last command done in Fish Shell

    - .local/share/fish/fish_history
- cmd: tail -n 5 .local/share/fish/fish_history | sed -n -e '/- cmd/,$p'
  when: 1513443643
  paths:
    - .local/share/fish/fish_history

I need to get the last line starting with - cmd: and get the actual command

using only POSIX

I'm writing a plugin

tail -n 5 .local/share/fish/fish_history | sed -n -e '/- cmd/,$p'

I did this

But that:
1. Doesn't get me only the line I need
2. Get's more than one - cmd: lines

(i.e. tail -n 5 is the minimum to get the last cmd with certainty but may also get more than one cmd line)

vzn

6:03 PM

in theory salon, 2 hours ago, by vzn

BREAKING: Engineers Just Unveiled The First-Ever Design of a Complete Quantum Computer Chip --- The Moon landing of quantum computing. / sciencealert

Mithrandir24601

@vzn Original article: nature.com/articles/s41467-017-01905-6

Anonymous

@Mithrandir24601 Si is way too versatile :)

dmckee

@BernardoMeurer Something like /^-/{a=gsub{"/^- cmd: /",""}}END{print $a;} perhaps?

That should sequentially examine lines in the input (basic awk processing loop) and when it find one starting with - saves in less the prefix to variable a. When processing is done it will print $a which contains the last line of that character.

Haven't tested it though. I'm grading.

Bernardo Meurer

6:31 PM

@dmckee Trying it out

syntax error on the second {

I think it's supposed to be a (

Bam

Hmm it's getting the wrong part

It seems to get the last thing starting with a -

@dmckee Why all the ^- ?

~  tail -n 5 .local/share/fish/fish_history | awk '/^-/{a=gsub("/^- cmd: /","")}END{print $a;}'
    - .local/share/fish/fish_history
~  tail -n 5 .local/share/fish/fish_history
  when: 1513449505
- cmd: tail -n 5 .local/share/fish/fish_history | awk '/^-/{a=gsub("/^- cmd: /","")}END{print $a;}'
  when: 1513449509
  paths:
    - .local/share/fish/fish_history

Emilio Pisanty

@vzn Is that really the best news source you could possibly find that covers that development? There's a purported game-changing development in quantum computing, and the best news source available is a science tabloid?

Bernardo Meurer

@dmckee That's what I mean

dmckee

Ah ... There should be a ; next in the action.

Emilio Pisanty

Or, if you just wanted to link to the press-release material, why not just link to the press release itself?

dmckee

So /^-/ says "apply the following actions to any line you encounter that starts with a -. Though it seems to be allowing white space which is not desired.

Bernardo Meurer

6:40 PM

Where?

dmckee

/^- cmd:/{a=gsub{"/^- cmd: /",""};next;}END{print $a;}

Bernardo Meurer

That yields the same output :/

awk is so weird

dmckee

Awk works with an implicit line processing loop. First in runs actions connected with BEGIN, then it compared every line in the file to a set of selectors (which may be null) and runs each action on matching lines (unless it encounters a next), Then it runs things associated with END;

Bernardo Meurer

I see

dmckee

Oh. Awk doesn't believe that ^ in a regex forces beginning of line. Try /- cmd:/{a=gsub("/- cmd: /","");next;}END{print $a;}

Bernardo Meurer

6:45 PM

It now gives me just the hyphen, lol

-

Emilio Pisanty

@BernardoMeurer what's ?

it blank-squares on my machine

dmckee

Maybe I am mis-using gsub. It's been a while for me.

Bernardo Meurer

@EmilioPisanty You need powerline fonts, it's a right-pointing triangle

One second

Emilio Pisanty

@BernardoMeurer what's a powerline font?

and what do you eat it with

Bernardo Meurer

@EmilioPisanty I guess the best way to explain is to show you my terminal

Those neat characters on my prompt are the "powerline"

Emilio Pisanty

6:48 PM

btw, can either of you fine gentlemen help explain why this answer and this one made score 10 and 25 recently but did not develop into either badges or hats?

Bernardo Meurer

And that bar at the bottom of my VIM

dmckee

@EmilioPisanty Not a clue.

Emilio Pisanty

@dmckee =|

let's see if the Tavern on the Meta folks can say something useful about it

vzn

Dec 12 at 17:04, by Slereah

Emilio Pisanty

@vzn ... . This is a serious issue. You are being called on for behaviour that's just short of vandalism and spam. Here is a chance to seriously defend your position. If you're actually interested in debate, take that chance.

Or, you know, just blithely link to other instances of people being extremely annoyed by your behaviour.

Bernardo Meurer

6:57 PM

@EmilioPisanty You didn't even praise me for my stylish terminal :(

And beautiful usage of powerline

Emilio Pisanty

@BernardoMeurer it is a stylish terminal

Bernardo Meurer

@EmilioPisanty Thank you very much :)

Emilio Pisanty

what are the different coloured segments for?

different folders?