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00:00
'cause logarithmic derivative
You can't be sure? OK, sure.
So double verification.
$d$ is the differential operator (I only saw a single d there)?
So you only need to prove it for something with one root and no poles
'cause you can multiply and divide stuff together
And, uh, I guess you can assume that root is at zero?
And you can always write it as $z^k$ times some analytic thing
and we can ignore that analytic thing
so we just need to prove it for $z$, really
And then that's just knowing how $\int1/z\ dz$ works
The "enter" key and the period key on the keyboard do the same thing
.
(is befuzzled)
@TedShifrin I think this is where I'm stuck: so we know that $q \perp 1$. Cool. But what does this do with $\log p$? AFAIK there's no relationship between $q$ and $p$, other than that you're moving from the maximum point $p$ in the direction of $q$
00:03
They serve the same function
They end sentences
I see
The "enter" key is more versatile, though
as it can end clauses as well
It means that $\log p \perp q$ for all $q\perp 1$. What does that tell you? @Clarinet
mobiles don't have that, though ,which is why when I am on mobile, my messages will become very short
because you cannot linebreak on mobile to get past that word limit
I'm not linebreaking, I'm legit starting a new message each time
You can copy/paste from Notes if you really need to, though
00:05
yup I know, I am just saying whatever that first comes to mind when I read the messages
Why's it called the argument principle, I wonder?
Same reason angle is called argument when you write $\text{Arg}(z)$.
> The argument principle can be used to efficiently locate zeros or poles of meromorphic functions on a computer.
Ooh, cool
DogAteMy: Did you ever email my former student at Yale?
@TedShifrin If $\log p \perp q$ and $q \perp 1$... then I see that the integral is equal to $0$ (already given)...
00:07
One moment
Quantifiers are important, Clarinet. for all $q$ with $q\perp 1$ ...
Think about subspaces in $\Bbb R^n$.
If $x\perp w$ for all $w$ with $w\perp v$, what do you conclude?
@TedShifrin Forgive me if I'm wrong on this (it's been too long), but intuition is suggesting that $x$ is a linear combination of $v$, perhaps with a constant vector added to it
Say what?
@TedShifrin Okay, I'm digging out the linear algebra text
Draw a picture. You have a one-dimensional subspace (spanned by $v$). For all $w$ orthogonal to that, $x$ is orthogonal to $w$. How can that happen?
(What's going on is $V^{\perp\perp}$ for subspaces $V$, in more generality.)
00:11
Right, and the orthogonal complement of an orthogonal complement is equal to the original subspace
@TedShifrin Yes
Well, it's true in $\Bbb R^n$ and it's true for closed subspaces in Hilbert space. So what do you conclude here, @Clarinet?
DogAteMy: Did he answer?
Not yet, I emailed him pretty recently so he probably hasn't seen it yet
Ohhhh ....
If I counted correctly, he should have one more year at Yale, DogAteMy.
@TedShifrin Well... $1$ and $\log p$ must be in the same subspace...
00:14
Right, @Clarinet. In other words, $\log p$ must be ... ?
@TedShifrin A CONSTANT! o_o
Finally!
Oh. You prove Rouche with homotopy?
I probably knew that at one point and forgot it
@TedShifrin Thank you for your patience and help with that. If I ever wanted to actually learn this stuff in the future... do you have a suggested text?
00:16
(That's the one where $|g|<|f|$, and $f$ and $f+g$ go around the origin the same number of times)
One can, DogAteMy. One need not.
@Clarinet: I have a bit on calculus of variations in one section of my diff geo notes, but there are classic texts. Fomin & somebody ...
You know how $(-1)^{n/2}$ generates alternating signs for even $n$. Is there a way to do the same for odd values of $n$?
'cause $f+tg$ is a homotopy between them and the winding number is homotopy invarient
I guess Olver wrote a book, too, Clarinet.
DogAteMy: You'd better be careful where the hypothesis comes in.
@TedShifrin K, so the same as the MSE recommendation. I'll have to buy it sometime
Thanks again
00:17
The hypothesis is needed to show that $f+tg\ne0$ for $0\le t\le 1$, right?
Could be :P
@TedShifrin I was wondering do you know why adjoint operator is useful other than for proving things ?
@TedShifrin This also explains why $p$ can't have infinite support... no constant over will integrate to $1$ over $\mathbb{R}$!
I heard they represents useful things in physics
It makes so much sense now!
00:18
as like observables and stuff
@Clarinet: So wait. Doesn't that mean there is no maximum?
I had been wondering for the longest time why everyone said "if you restrict to the set of all probability density functions in $[a, b]$, you get..."
You don't mean infinite support. You mean that our functions are defined only on a finite interval.
(well, "everyone," meaning every source I found online)
@TedShifrin Heh, yes
What I mean to say is that the random variable cannot have support over $\mathbb{R}$
Karim: That's self-adjoint, I believe.
00:21
hi
oh yeah
@Clarinet: I cheated, actually. I used compact domain to get $\perp 1$ earlier.
heya @Meow.
@TedShifrin Well, thank you again. Now after two weeks... I finally managed to finish Ch. 1 of this machine learning text. It's been a humbling experience. Grad-level stats, some hard probability questions, time series, Fourier analysis, and ending with calculus of variations in this one chapter of exercises
Well, learning can be exciting.
Learning is awesome
I wish life is just books and one can learn everything
00:23
learning sucks
nooo
It's really exciting because I've never used Fourier analysis or time series or calculus of variations before doing this set of exercises
you don't mean that, Eric.
so it's a good excuse to learn them
00:24
calc of variations is dope
Understanding is the reward of learning.
You should have been here to help Clarinet, Eric. He was stuck with me.
ah
im not great at CoV, i know the bits that have come up in my geo and PDE journeys
1
Q: 100% of the real numbers between 0 and 1 are irrational

Itay SelaI've once read a proof about this and I'm trying to remember how it went. We want to show that if we randomly select a number x from the set [0,1], then P[ x is irrational ] = 1

Someone posted a totally unintuitive yucky plane diff geo question on main, Eric. There must be something elegant/interesting about it. Look at it.
00:26
I really wish I had done grad school in math. Stats is interesting and is very practical... but it's just not the same
ive been meaning to spend some dedicated time learning some, but i guess i probably know a bit more than normal :)
Eric: You should look at Griffiths's little book on moving frames and CoV. I already mentioned it to you.
this is a weird question
Eric are you doing geometry?
oohh i should omg
00:27
hmm... I have no idea how one can query about how evenly the irrationals are distributed in some interval [a,b] since uniform distributions are not defined in the reals
geometry is my muse my dude
Yeah, it looks totally yucky when I write it out, @EricSilva, but maybe there's something interesting going on if you approach it right.
Can anyone provide me with a sanity check: If I have a homogeneous system of differential equations with non constant coefficients. What does it mean if the determinant is zero?
good that more people are doing geometry than bunch of algebraists haha
What determinant, @Rumplestillskin?
00:28
hmm maybe, ill draw some pictures and see if i get anywhere
Gotta bring my algebraist friends to chat to compete @Adeek
@TedShifrin how do you mean?
there's also the extra complication that every interval contains uncountably many irrationals, thus even if some of them have less irrationals, it is still uncountably many, thus basically it is quite intuitively even
hehe @Daminark
@Daminark watch ted's lectures
00:29
I'm asking what your question means, @Rumplestillskin.
algebra is good too
it's just not as good
yeah exactly
but then, the irrationals in the cantor set are not evenly distributed because clearly the middle third of the interval [0,1] has no numbers in it
Ah excuse me. I have a system A x = 0. where x is a vector of first order derivatives. A is a matrix. The determinant of A is zero and I need a sanity check to verify whether this mean we do/don't have a solution. @TedShifrin
Don't you mean $dx/dt = Ax$, @Rumplestillskin?
00:32
@LeakyNun Are the irrationals "evenly distributed" in the reals, in that pick any interval [a,b] where a=/=b I am guaranteed to find uncountably many of them?
Nope the system is A x = 0 where x = [df/dx dg/dx dh/dx].... This is okay right?@TedShifrin
@EricSilva: I think that guy got the question from a Brazilian text.
@Eric and @Adeek kek
Terrible to use x in both places, @Rumplestillskin. Can you please start at the beginning of the problem, not the end of it?
:) @TedShifrin this is of course not the real problem this is just it's form. The real problem is quite large. But it's a homogeneous system of linear differential equations with three unknowns a' b' c'. This is my x vector. where prime indicates derivative with respect to xi. the coefficients of a' b' c' make up the matrix A. The determinant of A is zero.
00:36
his name sounds brazilian as hell
Yeah, and the author of the text is Keti Tenenblat, who's been in Brazil forever. I know her from my Berkeley days. Chern mentored her for a few years.
Well, @BalarkaSen isn't here to hear my hypothesis testing rant :P
hmm i cant seem to find the text he mentions
oh she is turkish @TedShifrin
And you're asking about $Ax=0$, @Rumplestillskin? In linear algebra, this will have lots of solutions when $\det A = 0$. Write down some simple examples. You'll get the corresponding subspace of solutions with $a', b', c'$ ...
00:38
I am part turkish and greek
Generalized inverses! Wooooo
@EricSilva: The name of the text appears on her Wiki page. I know some books that are more advanced.
Small world, Karim :P
yeah haha
oh i see i was looking for it under the english title but maybe there isnt a translation
I don't think there is.
00:40
Yes that's what I thought. We have an infinite solution space for det(A) = 0. @TedShifrin
no problemo there
Seems so to me, @Rumplestillskin. Do a simple example.
And she does moving frames, ERic ... :P
good stuff
She and Chuu-Lian Terng did some stuff on PDE and moving frames years ago.
ima take a look at this text
00:42
Can you find it in Portuguese?
yup
hmm the problem is just the last problem in the section on Frenet Formulae
it doesn't seem like it's amenable to vector approaches
this problems is mega unintuitive to me
me too
the $1/\kappa$ gives a horrendous differential equation ...
00:50
@Secret Yes
Every interval contains uncountable many irrationals
Notice that every interval $(p,q)$ with $p,q\in\Bbb Q$ is isomorphic to $(0,1)$, in the sense of the existence of a bijection which sends rationals to rationals and irrationals to irrationals
and notice that every interval $[a,b]$, $a<b$ contains an interval $(p,q)$ as above
@TedShifrin getting a lot of emails from students about TA duties
few students didn't put their name on the last assignment and I am trying to figure out who
students are careless sometimes
one thing I don't quite know how to formulate (or whether it is sensible at all) is how to find whether a given set of number "bunch" at some location of the number line because of the difficulty introduced by infinite cardinals. for example the harmonic series in [0,1] is countable, but it has a limit point at 0. The cantor set is uncountable, but there are intervals where there are no numbers thus the irrationals are effectively concentrated at the pseudoboundary and the interior.
I am not sure if there's a mathematical quantity that captures this
sometimes?
altough I am not organized at all but I was never careless though
atleast with my assignments
A student in a class I TAed once emailed me his pset despite living two doors down from me
00:56
@AkivaWeinberger It is known every real is an accumulation point, but does that guarentee the "bunching" is uniform in some way?
@Ted I think I've lost interest in this curve question
I like to write comments (in red) when I grade, so .pdf homework sucks. I have to print it out and it never prints well unless it was TeXed to start with.
me too, @EricSilva.
I was just curious if you saw something I didn't.
@Secret The fact that every $(p,q)$ is isomorphic to every other should imply that it's uniform
tried to take a derivative and got bored
00:57
I like my exercises better :P
Just a linear transformation between them
LOL ... but you bore easily.
true lol
I see, never thought I can use isomorphisms to check that
I like to write comments in TeX so i like when students send me TeX files
but not everyone TeXs
00:58
Mostly not.
my dreams always lead to these weird questions that otherwise I never thought about
it is good I can actually learn from them
if i were teaching I would maybe offer a tiny bit of bonus points if people TeXed, just because of how much easier it makes my life
I like(d) to grade papers away from computers, relaxing lying back in a chair ... so ... blah.
@TedShifrin Curve question?
that's fair
01:01
@TedShifrin I like to grade while sitting in on colleagues' classes
seems to make it a little more bearable
I'm sure they appreciate that
@TedShifrin if I grade near the computer I know I will procastinate
DogAteMy: This nutsy question.
I just shut down all electronic devices and grade so I can be effient.
efficient *
@TedShifrin The distance between Q and T probably ends up being a nice expression (I hope)
01:04
Yeah, that part isn't so bad, DogAteMy.
As I indicated in my various comments.
Ah, grading. Haven't done that since my undergrad. One of my professors, when he graded his first exam (not for my class), accidentally spilled beer all over the students' exams. I can't remember if they were still readable
LOL ... sure he did.
i feel like beer is a bad grading drink
I chose martinis.
Huh. I knew your name looked familiar. I've been using your text, along with do Carmo's "Differential geometry of curves and surfaces" for supplementary reading (although I haven't done as many problems). It is really good indeed! — Matheus Andrade 2 hours ago
Still find it amazing that we have a book author hang out regularly in chat
01:07
i feel like i would need something really hard to get through the nonsense
Hey @TedShifrin just sanity check If we compute $\|T\| = sup \{ |(Tx,y)| : \|x\| = \|y\| = 1\}$ then it is true that $\|T\| = sup \{ |Re(Tx,y)| : \|x\| = \|y\| = 1\}$
yeah it is true
Eric: How's vodka sounds to you?
I prefer gin to vodka. Speaking of which ... it's time for it.
I had plenty of wine last week after my experimental design final
heh
So glad that class is done -_-
Some festive holiday music for you all:
What's "experimental design"?
01:13
@Akiva Good question. Do you know what a variance is?
Wait, is this [experimental design] final or experimental [design final]?
[experimental design] final
@Clarinetist No. Something statistics-y?
Like a standard deviation
@AkivaWeinberger Pretty much. So the square of a standard deviation is variance. The idea behind experimental design is that you want to perform an experiment: i.e., you have some units onto which you want to perform various treatments. How do you design your experiment so as to minimize the variance of your estimates? This is desired because you want your estimates to have as little variability as possible
@TedShifrin Thanks this is exactly what I thought except colleague of mine is quite adament this is not the case! So I was doubting myself!
01:17
@Eric Probably depends on what type of nonsense. It's half cringy and half funny
i wasnt serious
Lol but yeah at some point I'm gonna try to learn how to write comments on pdfs
@Clarinetist Ohh. Designing experiments, not making designs in an experimental fashion
@AkivaWeinberger By "estimates," I mean quantifying the impact of your treatment
@AkivaWeinberger Yep, that's correct
I was thinking of, like, the phrase "experimental music"
01:20
Has anyone listened to that vid I put up??? :o
I can't right now
@Clarinetist Very different to the cheerful version we often heard
@Secret Yes, it is! I think it's a very interesting take
In other news, it seems pdf with vertical asymptotes are rarely used
despite for some of them, a lebesgue integral exists for such functions
Yeah, I can't think of one time where I've seen a PDF with a vertical asymptote
01:31
but again, had it not because of the dream last night, such question will probably never came into mind which showed how I am so used to thinking pdfs must be lack of vertical asymptotes always (well it is the case in physics)
Last night dream claims the irrationals has the following distribution on the real number line:
I am guessing my brain probably spend too much time thinking about complex systems and the notion of criticality since that complex system symposium in 11-13 dec
Akiva and I then worked out a few minutes ago that such claim is false, though
Anyway, I think if there's a place where unbounded pdfs were used, it might look something like a mix of exponential and hyperbolic and starts or asymptote at zero because that is the most physical scenario I can think of
oh no .. it's @orbit
(The other lines are numbers that are labelled in the dream, but the dream have gave no elaboration of them and the actua labels are so cluttered that one can only remember show much from a dream. (meaning I don't recall their exact positions except they form a cloud clustered near the base of that graph))
Fascinating
The last vivid dream I had was maybe a week ago. Before that, 4 years
ish
:O 4 years!
I can remember nearly all my dreams as I have dreams almost every single night (those night where I don't have dream I will see blackness or I won't aware I have been asleep). Idea dreams like the above (and with such rich amount of not too wrong math content) remains rare, though
01:39
Yeah, it was weird to have such a vivid dream last week. My music theory professor became an optometrist. Was telling his students to look through a microscope in class to test our eyes
I think I've caused my former students some nightmares.
I think it was because I woke up in the middle of the night - my wife was up at 2am with the lights on
Oh sure, blame it on her.
@TedShifrin lmao
01:40
Usually, dreams tend to be easy to remember when you are being jotted awake when fast asleep.
thanks, ERic
For me, the outcome is mixed
I've had - not really vivid dreams about missing a class that I enrolled in for an entire semester and failing it
It was usually a history or English class
I think most grad students dream about sleeping through their qualifying exams or thesis defense.
Thankfully I haven't had that one ^
01:42
I have fail the exam or fail the test dreams on biology, english, chinese and sometimes maths
I must be too well-adjusted.
they usually are a warning, meaning I have something important I need to do that I keep procrastinating away from
I feel like I'd be paranoid about that
you, paranoid, Eric? Hard to believe!
I sometimes fall asleep at inappropriate times
01:43
My wife is deriving the unit circle in preparation for Calc. I next semester
(i.e., the $\sin$, $\cos$, and $\tan$ values)
I've missed things because of it before
Weird to think I did that 9 years ago
I am teaching precalculus this year, Clarinet. I think I have those down.
Is she a teacher or a student?
But we've moved on to complex numbers, then vectors and linear algebra.
Fun. No, she's a student. Studied music back in her undergrad, going back to school to do CS
01:44
As for nightmares, I had 5 nightmares in the past 8 years which felt like they are actively trapping you in them and preventing you from escape even if you have reality warping abilities
The one thing that I'm glad my Pre-calc teacher did was make us derive the unit circle values using the 30-60-90 and 45-45-90 triangles using only a pencil and paper. Told us that he didn't want us using calculators at all
@TedShifrin wow! Professor you are moving fast?
@Clarinetist how does one derive e.g. sin 15 from drawing those triangles, since it is one of the standard questions using common trig values
This is the AoPS syllabus.
Totally agree, Clarinet. And I showed my kidlets how to double the 30-60-90 triangle to figure it out.
Not standard, Secret, not at all. In fact, I've never learned that at all.
But one gets to double/half-angle formulas.
I personally don't believe in half-angle formulas.
Yeah, I would say use the half-angle formulas with the unit circle if you really want to do that
01:48
I don't believe in half-angles. :)
Just apply double-angle.
Oh. Why does that make so much sense? Lol
back in my high school days, we received questions like deriving sin 75, cos 75 wihtout calculators, but by that time we have compound angle formulae. I am not sure if one can do that purely geometrically though
I think too much priority is placed on memorization
I totally agree.
I didn't learn trig at all in high school. I had to relearn it from tutoring in my undergrad
01:50
But the AoPS course didn't make them memorize much besides what I approve of.
Should know law of cosines, law of sines, addition formulas.
$\theta^{..}$
@TedShifrin hello. I passed all of my math courses!
@Clarinetist what's the machine learning text you're going through called?
What it means 2 dots on theta?
heya @orbit. Congratulations. But I didn't think there was any doubt.
Perhaps the second time derivative?
01:51
@orbit-stabilizer Machine Learning by Sergio Theodoridis
What are the contents in your precalc courses? It will be interesting to see how that compared to australia's
@Secret: The course I'm teaching is not a typical high school or college course. Totally not.
@Clarinetist why did you choose this specific text? It's not standard
@TedShifrin I'm surprised how many textbooks don't describe the law of cosines in words. Whenever I tutor it, I say (a side)^2 = sum(other two sides ^2) - 2 * product(other two sides) * cos(opposite angle of your side)
Students, in my experience, seem to think that there are three different formulas
01:52
@Fawad that's indeed $\frac{d^2 \theta}{d t ^2}$
Um, I guess I've never done that, Clarinet.
Four students, right? @TedShifrin
@Fawad theta is the angle, you're looking at the second derivative of the angle w.r.t time
Yup, skull, but that's because the school just opened and high school level kids are too busy. The elementary classes are damn full.
@orbit-stabilizer Because I've read all of the standard texts, and I hate them. They are terrible to learn from, IMO
01:53
@Secret orbit is saying wrt to time
@Clarinetist like what?
@Fawad secret made a typo
sorry typo
@orbit-stabilizer Let me give you the list of all of the ML books I've at least skimmed through:
Oh, I see your point, @Clarinet. I only write one formula.
@orbit-stabilizer I've read the following:


Machine Learning: A Bayesian and Optimization Perspective (Theodoridis)
Pattern Recognition (Theodoridis)
Pattern Recognition and Neural Networks (Ripley)
Pattern Recognition and Machine Learning (Bishop)
Foundations of Machine Learning (Mohri et al.)
Understanding Machine Learning (Shalev-Shwartz, Ben-David)
Hands-On Machine Learning with Scikit-Learn and Tensorflow (Geron)
Machine Learning (Flach)
Make Your Own Neural Network (Rashid)
Modern Multivariate Statistical Techniques (Izenman)
01:55
Oh, you don't like ESL?
Or Hands on Machine learning with scikitlearn and tensorflow?
@orbit-stabilizer Nope. I think it's way too handwavy and is rather misleading in its preface for its prerequisites
Professor, I saw "common core math for kindergarteners" the other day :-D @TedShifrin
I found the Hands On book good for actually writing code.
I have only done the first chapter, but I found it really helpful.
@orbit-stabilizer For the TensorFlow one, yes, that's the best one for code. Completely agree there. I needed a theory-driven text
Its theoretical discussions, IMO, are pretty good, but not where I needed to be
01:56
Yeah, totally agree there haha
In my grad class, I'm going to be expected to know the "by-hand" details of these algorithms. Starting it in a month.
I'm surprised you find ESL hand-wavey, I thought it was a pretty standard text for intro ML
Have you taken a look at this?
So it turns out open mapping theorem makes max modulus quite easy
@orbit-stabilizer Yes, it is. But I imagine most of the people reading it don't really know the details behind what it says. I've actually tried doing the algorithms by hand using what's in ESL and it's insufficient
Most of the people I know reading ESL have only skimmed it for a high-level understanding
Though my complex prof said he prefers the way he did it since it works for harmonic functions
01:58
@orbit-stabilizer Yes, I have that book. Haven't had a chance to really read that one
To me ESL = English as a Second Language
ESL = The Elements of Statistical Learning

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