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17:01
@ACuriousMind Maybe you just don't understand QFT as well as you think, sorry.
Jan 14 at 6:17, by DanielSank
You are such a troll.
😚 only for you
::wonders if emoji renders on desktops::
@0celo7 There's a unicode character looking like a face there, yes. The unicode character is U+1F619 "KISSING FACE WITH CLOSED EYES"
Ah, good.
Just a wee bit gayer than it seemed in my head, but oh well
How did you identify the Unicode character?
I googled it.
17:08
Oh for the love of Christ :D
@0celo7 that's politically incorrect
@FenderLesPaul Your face is politically incorrect
At this point I just have to smile any time I see anything about Erdogan in the news. That mofo is crazy
@0celo7 that's racist
and ableist
Oh you're disabled? So?
Mentally disabled?
:P
Also pretty sure guitars aren't a race.
Iran is going to ruin all oil countries.
RIP Canadia, @HDE226868 @0537
17:31
@0celo7 the site is taking forever to open
:(
oh it opened
haha
crazy people errywhere
@ChrisWhite Reddit says comets can't explain that star.
@0celo7 "grammarless wolves" ::chortle::
i see that it's possible to change the displayed name. what would happen if i changed it, to the people who have commented out by calling my current name? Will their message auto transform to calling my new name or not?
Of course grammar matters, but it matters for a reason (to whit: it makes communication less ambiguous) and not for its own sake.
@dmckee I love the part where he calls people "pussies" for...some reason
17:44
@no_choice99 No @-tags are not munged. Experienced users can generally deduce the changes, and some people change to New Name -- oldname (or something similar) either indefinitely or temporarily.
Munged?
Mung or munge is computer jargon for a series of potentially destructive or irrevocable changes to a piece of data or a file. It is sometimes used for vague data transformation steps that are not yet clear to the speaker. Common munging operations include removing punctuation or html tags, data parsing, filtering, and transformation. The term was coined in 1958 in the Tech Model Railroad Club at the Massachusetts Institute of Technology. In 1960 the backronym "Mash Until No Good" was created to describe Mung, and a while after it was revised to "Mung Until No Good", making it one of the fir...
I can Google.
@0celo7 The chat transcript casts doubts on that :P
But tbh I don't see how that applies here.
17:46
But this way you know which meaning I intended without ambiguity.
I must be getting old.
thanks @dmckee interesting
wow ducklings are too cute
d'aww
seriously...
leave if you don't like it
17:53
=(
The concept of an orthogonal matrix and of diagonalization are standard linear algebra concepts. Relativity texts usually expect you to be familiar with linear algebra. — ACuriousMind 22 hours ago
@ACuriousMind "usually"
I think even Zee requires some knowledge of matrix algebra
@ACuriousMind Umm, since when can't you use SR in non-inertial frames? physics.stackexchange.com/a/148497/59215
@ACuriousMind well gee
@ACuriousMind how do you do it
Hello folkses
@BernardMeurer turns out that inequality was trivial
dunno if you were here to see it
18:00
@0celo7 The one causing your brain to hang itself?
Yeah
Dr. Bajoran figured it out instantly
And how did the proof go?
The proof of $|a|-|b|\le |a-b|$ was easy and I already had it.
Note that this also implies $|b|-|a|=-(|a|-|b|)\le|a-b|$
Hi everyone, When writing a paper for a journal, is it frowned upon to put "we" . As an example ... "We now examine the last method..." etc? Or is it better to put "the last method is..."
So if $|a|-|b|\ge 0$, the problem is done. If $|a|-|b|<0$, then $||a|-|b||=-(|a|-|b|)\le|a-b|$, so $||a|-|b||\le|a-b|$ holds in general.
@ACuriousMind the fastest links in the galaxy
@BernardMeurer ikr
how does he do it??
@0celo7 I see, cool proof. I'll get you some more inequalities, last night was fun hahaha
Yeah I was wondering how can he do it so fast
@BernardMeurer do not give me more >:(
although just explain the $\sqrt{x+y}$ one please
@ACuriousMind Perfect :D
18:09
@0celo7 $\sqrt{x+y}$?
yes
$\sqrt{x+y}$ and $\sqrt x +\sqrt y$
Oooh
The one I proposed yesterday?
no
the one ACM used in his proof
18:11
Hell, I don't understand what @ACuriousMind does I just trust the man
@0celo7 Look at $(\sqrt{x}+\sqrt{y})^2$.
@ACuriousMind Yeah yeah
what about it
Looks nice, doesn't it. Almost begging for a binomial formula to be applied to it.
what's that
::draws triangle::
according to my calculations that should be $x+y+2\pi\sqrt x\sqrt y$
$x + 2 \sqrt{xy} + y$?
18:13
no, I think there's a $\pi$ there
@0celo7 ?!?!?!?!
Where did you get $\pi$ from?
Pascal's circle?
Isn't that how you do this?
Stop trolling :P
My goodness
18:15
@ACuriousMind I figured out the squaring trick as soon as I asked the question again
@BernardMeurer I'm not a troll.
Don't listen to ACM's harsh, harsh words
@0celo7 I'm brazilian, I have a troll 6th sense and it tingles when you're online
so what's the proof that $\sqrt x\sqrt y=\sqrt{xy}$
@BernardMeurer uh, what?
@BernardMeurer lol
I wonder if I can sue you guys for defamation
@0celo7 Yes :)
18:19
@0celo7 In brazil it's only a crime is someone ends up dead in the process
Can you win?
No :)
Everything else falls under comedy
Note to self: Don't go to Brazil.
@ACuriousMind I wish I could have that on my notes
oi
tudo bem? xD
18:21
Let me guess, you speak spanish do you not good sir?
yes as 2nd or 3rd language
But also the glorious and all-powerful portuguese?
nope only a few words
"o pais maiz grande do mundo" :D
that's some stuff i know about br
Hahahahaha
big culture, good food, etc
18:25
My list of countries to not go to is pretty big
It also includes some US states
would you go to israel?
and vatican
and poland
The only place I'm never going to in Tennessee
@0celo7 lives there
LOL
honestly i have difficulty with religion. i don't think i could ever live in a place where religion is all over the place
but that's just me i guess
like the 3 countries I've mentionned. i think religion is all over the place there
maybe not in tel aviv, i don't know
18:30
@no_choice99 No to Israel, yes to Vatican, Why would anyone want to go to Poland?
well they have oscypek and good landscapes and good climate
problem is religion
cof Women... cof
Good climate? Isn't it freezing there
that's what i call good climate
Damn Euros
18:34
good for the mind
lungs, etc
It needs to be a dry heat
best for studying physics
yeah it's easier to do physics in the winter.
i agree
@0celo7 Scandinavia has excellent climate
18:35
Scandinavia is the most beautiful place I've ever been to
@ACuriousMind You're a freaking Viking, ofc you think that
@yuggib Heading off to the library to give my PDE text a read (and do homework ugh). I'll give a report.
The nicest place I lived was San Antonio, Texas
Hot and dry
Not the swamp I currently live in
@0celo7 It's cold there today.
@BernardMeurer did you begin qm?
@0537 how cold
@yuggib It's typeset in LaTeX so that's already a plus
@0celo7 -3 to -12 celsius.
@0celo7 well, that's indeed a minimal requirement for post 1980 books/papers
18:42
@yuggib wtf they write out multiple integrals
fahrenheit temperatures are retarded.
@0537 kinda like you
T_T
wow.
Too much?
18:42
:(
@yuggib no hilbert spaces or anything
Oh Jesus Bessel functions
well, I imagined that
a sort of TeX typeset fairytale
you wanted engineering style? :-D
Meh
I'll take the analysis based one later
::nods in approval::
I mean, that was always the plan
18:46
I know
And I was supposed to take topology instead of PDE but they took it off the schedule
why?
Not enough people probably
general topology is not good enough for UTenn?
They're doing the second semester, etc. topology courses
So next semester they'll be offering the intro course again.
18:48
so you will learn what a tonnelled space is another time ;-)
But then I have to take a required star course for my degree and won't have time
So I'll have to wait until my third year for topology, most likely.
*stat course
maybe in english is barelled space
@0celo7 Do you have some random time stamp generator telling you when to ping me?
@HDE226868 How did you know about that D:
@0537 Not yet, have classes to give today :(
18:56
What is a phase factor?
@StanShunpike $\mathrm{e}^{\mathrm{i}\phi}$, $\phi\in\mathbb{R}$
@StanShunpike i.e. a complex number of unit modulus
why can't i see latex images in this chat?
you have to believe in God to see them, my son
noooooooooooooooooooooooooooooo!!!!!!!!!!!!!!!!!!!!!
i'd rather die :/
i see @HDE226868 I'd need to install stuff
thanks
19:05
@no_choice99 It ends up taking ~15 seconds, max.
@yuggib Chapters: Heat Equation, Method of Separation of Variables, Fourier Series, Wave Equation: Vibrating Strings and Membranes, Sturm-Liouville Eigenvalue Problems, Finite Difference Numerical Methods for PDE, Higher-Dimensional PDE, Non-homogeneous Problems, Green's Functions for Time-Independent Problems, Infinite Domain Problems: Fourier Transform Solutions of PDE, Green's Functions for Wave and Heat Equations, The Method of Characteristics for Linear and Quasilinear Wave Equations
@yuggib Laplace Transform Solutions of PDE, Dispersive Waves: Slow Variations, Stability, Nonlinearity and Perturbative Methods
@no_choice99 Do you not see how horribly rude such a comment is? Jeez.
the index seems reasonable
that sounds boring as fuck
but it is indeed a "physical" approach
We don't cover anywhere close to all of that in one semester.
It's a 700+ page book
19:12
I hate it when I get food on my pants
ughhh
how will he define the Green's functions without distributions?
let's see...
we don't cover Green's functions until the very end of the course
oh jesus
$\delta(x-x_i)=0$ for $x\ne x_i$ and $\infty$ for $x=x_i$ :D
T__T
he basically defines the Green's function as a thing s.t. $\int f(x)G(x,y)\mathrm{d}y$ is a solution of the PDE
I mean, this is pretty much what physics PDE is, cf. any QM or QFT book that's not German
mmh...not convinced but maybe
19:18
also: the library is closed
now I have to sit in the dorm and read...not fun
someone be starring things
@0celo7 haha
ask for an office
I'm a Freshman...
@yuggib how does one prove that if $f$ is nonzero and of one sign over the inverval $I$, then $\int_I f$ is nonzero?
@0celo7 using the definition of integration
@yuggib Riemann sum?
weeell, probably also with the Riemann sum definition
19:30
what's the definition of integration if not a Riemann sum
I'm not talking about Lebesgue here
@0celo7 what is it physically?
@StanShunpike the Riemann sum or phase factor?
@0celo7 measure-theoretic definition is rather different
@yuggib well I'm not a measure theorist
oh my god why is there a girl sitting in the study room texting
not even reading or doing anything
@0celo7 Sounds pretty much in line with someone sitting in the study hall chatting
19:34
@Asmyldof I'm currently reading about boundary conditions on rods
@0celo7 so?
don't set limitations
reach for the stars
is that like a reacharound
@0celo7 If you were the slightest bit pedantic enough to be a scientist you'd realise that while typing that sentence, no you were not.
@Asmyldof I have two eyes
19:41
@0celo7 Only one of which is good at reading
@Asmyldof no, both can read
@0celo7 I think that a non-zero $f$ of one sign over an interval $I$ can have zero integral
Does anyone else think the capital C in computer modern looks strange?
@yuggib continuous
continuous is boring
@yuggib what was your counterexample going to be
19:48
of course non-continuous
ok?
what was it going to be
$f(x)=\left\{\begin{aligned}&1, x\in\mathbb{Q}\cap I\\&0\text{ otherwise}\end{aligned}\right .$
Modified Dirichlet?
well, I don't know Dirichlet but probably
Dirichlet is the function which is unity on the rationals and vanishes on the irrationals.
19:55
ok, so it's dirichlet function
yeah but can you Riemann integrate that
yep
it is continuous almost everywhere
wat
I thought it was everywhere discontinuous
(restricting attention to $I$)
In mathematics, a nowhere continuous function, also called an everywhere discontinuous function, is a function that is not continuous at any point of its domain. If f is a function from real numbers to real numbers, then f(x) is nowhere continuous if for each point x there is an ε > 0 such that for each δ > 0 we can find a point y such that 0< |x − y| < δ and |f(x) − f(y)| ≥ ε. Therefore, no matter how close we get to any fixed point, there are even closer points at which the function takes not-nearby values. More general definitions of this kind of function can be obtained, by replacing the absolute...
the points where it is discontinuous are the rationals, which are isolated points of the reals
and countable
so their (Lebesgue) measure is zero
Lebesgue?
Scummy move, I said no Lebesgue
20:02
it does not matter
the Riemann integral is defined for every function that is continuous apart a set of points of (Lebesgue) measure zero
we will continue this in a semester
In the branch of mathematics known as real analysis, the Riemann integral, created by Bernhard Riemann, was the first rigorous definition of the integral of a function on an interval. For many functions and practical applications, the Riemann integral can be evaluated by the fundamental theorem of calculus or approximated by numerical integration. The Riemann integral is unsuitable for many theoretical purposes. Some of the technical deficiencies in Riemann integration can be remedied with the Riemann–Stieltjes integral, and most disappear with the Lebesgue integral. == Overview == Let f be a non...
follow the link ;-)
for all I know you wrote that article
no indeed I didn't
proof?
20:06
I hate riemann integral
it hates you too
Jesus the guy doesn't even \mathrm derivatives and e and i
@ACuriousMind He's a barbarian!
@yuggib is there no Picardy-Lindenhof theorem type thing for boundary value ODE problems?
boundary value?
o.o
ok I'm reading this on page 38 of an intro PDE book, I know you know what I'm talking about
ok for PDEs
not ODEs
no, for ODE
$\phi''=-\lambda\phi$, $\phi(0)=\phi(L)=0$
20:16
4 hours ago, by ACuriousMind
@FenderLesPaul Why is everyone saying that? Furry's theorem says that a diagram with an odd number of photon external lines connected to a fermion loop vanish. Some also use that for "the VEV of an odd number of EM currents vanishes". But that doesn't mean "all third-order diagrams vanish".
@ACuriousMind How does one see the connection between these two definitions? More generally, how is a VEV related to a scattering amplitude with real particles?
@0celo7 ok; I don't think so
To me as a noob these sound like two different theorems..
@Bass I think you need the LSZ formula.
@Bass Basically, the LSZ reduction formula gives scattering amplitudes in terms of time ordered vevs.
@Bass Are you using Zee to learn QFT?
20:38
@0celo7 Ah yes. Though in the case of Furry I don't find this connection obvious. Gonna need to check it. Thanks.
@0celo7 Yep, among others. I started with Zee, but mostly switched to other textbooks and lecture scripts. I think Zee is a good collection of cool heuristics, but its pedagogical value.. well..
@Bass Basically you'll get a thing like $M^{\mu\nu\cdots}=0$ due to Furry's theorem and LSZ, then the scattering amplitude is something like $M^{\mu\nu\cdots}J_\mu J_\nu\cdots=0$ IIRC.
Not guaranteeing anything.
Maybe with some integrals.
Zee does not even mention LSZ, which is a really important theorem in QFT.
@yuggib The book pulled the ol' "here's a Fourier series...oh look, we solved the heat equation" :D
Precise details will be covered in chapter 3, ok
Wonder how precise
@yuggib "We must discuss the convergence of these series [...] For the moment, let us ignore these somewhat theoreical issues"
@yuggib he just moved an integral inside of an infinite sum, is that allowed
21:23
@FenderLesPaul I'm not even ready for last week
@0celo7 For exchanging limits (which an infinite sum is) with integrals, you need some kind of convergence theorem. One that is often used is dominated convergence
@ACuriousMind ahh, scary analysis
you know I'm allergic to that :(
don't give analysis links without a a trigger warning
@ACuriousMind Did you know that induction dates back to at least 1321
@0celo7 No, I have never spent a single thought on the history of induction
@ACuriousMind Well now you know :)
A Mister Levi ben Gehrson
@ACuriousMind erm, how does one prove the product rule for a non-integer exponent?
@0celo7 I don't understand the question. You can prove the product rule without ever assuming a specific form of the two functions.
21:34
@ACuriousMind oops, I meant power rule of course
@0celo7 You mean $(x^n)' = nx^{n-1}$?
algebra book wants me to prove it given the Leibnitz rule and an integral exponent
@ACuriousMind yes
@0celo7 Consider the derivative of $(x^{p/q})^q$ and use the chain rule to deduce what the derivative of $x^{p/q}$ is.
@ACuriousMind what if the exponent is irrational?
@0celo7 Approximate it by a series of rationals, obviously
21:40
>obviously
That's how you define exponentiation by an irrational exponent in the first place, so yes, I consider that obvious
oh really
well it's not obvious to me that it's obvious to you that one defines it like that!
...how would you have defined exponentation by an irrational exponent?
...I'd like to plead the fifth
I rest my case.
21:46
@ACuriousMind @0celo7 may I make a rather silly maths question? This problem is boggling my brains
depends what kind of math
I am currently contemplating suicide by inequality
If I have a certain debt $b$ that I must pay off and it has an annual interest rate $j$. How do I find out the minimal ammount I must pay in order to pay it off in exactly 12 months?
Oh jeez
That's the WORST math
There's a reason why bank tellers have PhDs
I'm trying to equate this disgrace but my brains are just giving up
wait what
21:49
Anybody around that can lend a hand on github?
12 months is one year...so just pay all of the principal
@EmilioPisanty bring it
@0celo7 Yes that's what I though, but the interest wont be applied equally since the debt decreases everymonth
@BernardMeurer So I forked a repo and committed to it
and I want to make a pull request
but for the life of me I can't find it
Annual interest rate $j$ means you apply the interest after one year
@EmilioPisanty the repo or how to make a pull request to the original branch?
21:51
I think
How exactly are you defining $j$?
@BernardMeurer How to make a pull request
@0celo7 but it's getting calculated monthly with an application of $\frac{j}{12}$
or hang on, maybe I didn't actually clone a repo, but a gist instead
whatever that is
@BernardMeurer is it applied at the beginning or end of each month
@EmilioPisanty Dang, idk how to pull gists. Let me check t out
21:52
like we start at Jan 1
is it applied on Jan 1 or Jan 31
And when are you making the payments?
@0celo7 It's applied at the end of the month
@BernardMeurer hah, yeah, that's why I can't find it, it's not doable
thanks for the patience
@EmilioPisanty anytime man
Alright, I got it.
@0celo7
Assume that the interest is compounded monthly according to the balance at the end of the month (after the payment for that month is made). The monthly payment must be a multiple of $10 and is the same for all months. Notice that it is possible for the balance to become negative using this payment scheme, which is okay. A summary of the required math is found below:

Monthly interest rate = (Annual interest rate) / 12.0
Monthly unpaid balance = (Previous balance) - (Minimum fixed monthly payment)
21:53
The solution is just an easy application of the debt equation
@BernardMeurer Let $M$ be a (paracompact, connected, etc.) manifold.
We define the bank tensor $B_{ab}$ on $M$ to be the energy-momentum tensor of the bank Lagrangian
3
@0celo7 TROLL
your problem is a simple application of the conservation of this tensor
fine, I guess you don't want my help
I got super excited on that first message hahahaha
I was thinking you had come up with some absolutely beautiful solution
What's the debt equation tho?
Einstein's equations for the bank

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