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03:17
@robjohn Hola
@Knight hey there
How are you sir?
Dinner done?
@Knight Doing okay. How about you?
@Sophie Thank you Sophie for your suggestion, and yes inlatexbot is working but the problem is that it's not working in a group. It's just working on it's own chat.
Here it is okay:
But here not okay:
@robjohn My aim is to get latex rendered on a chat app called Telegram. People say that they have developed bots (I really don't know if they mean a kind of program by that) which will convert our latex code to the images (like the first image above). But unfortunately it's not working.
 
1 hour later…
04:46
@Knight you should probably read their github page, it does not seem like you are using it correctly
 
3 hours later…
08:10
@CalvinKhor I read it, but couldn’t find my mistake. Can you please point it out?
@Knight
$\Large\textbf{Description and general usage}$

This bot converts LaTeX expressions to .png images when called in inline mode (@inlatexbot <your expression>) and then shows you the image it has generated from your code. Everything happens live, so you can just gradually type and continuously monitor the result. When expression contains errors, they will be displayed instead of the image. Finally, when you are ready, click or tap the suggested picture to send it.
See the screenshots, it should be what you see
@CalvinKhor Did I miss < > things ?
Please see the screenshot I took from the website, it answers your question @Knight
Oh! Double dollars
I suspect you still do not understand, but please give it a try
08:21
I got it Cal. The code and @inlatexbot has to be in one line and I must use single dollars
@Knight that was not at all my issue with what you showed in the screenshot this message replies to. In that screenshot, you have already sent the messages, whereas in the screenshot above, the message is not yet sent
Yes.
The above quoted description mentions "Everything happens live", which does not seem to be possible for sent messages, so together with the screenshot, i guessed you were doing it wrong
Okay you mean the people need to be online for that?
I really feel like I'm not getting through to you. Maybe someone else wants to try to explain it?
if it works, then we can drop it
08:32
@CalvinKhor InLatexbot has worked, but Latexbot is not working.
ok :) good
Thank you so much Calvin and to you too @Sophie
09:01
Hello all! I'm looking for a book that contains the following results:
Given a bijection between the points of two lines that conserves the double ratio, the geometric place of the lines that connect each point of one of the lines with its image in the other is a hyperboloid of a leaf. If the application also retains the simple ratio, then the site is a hyperbolic paraboloid.
Do you know books about this and its proof? Thanks!!
 
3 hours later…
12:32
@manooooh are you talking about cross ratios?
13:07
Let $V$ be a $\Bbb{R}$-vector space. In the paper I am reading, the author wants to "equip $V$ with a locally convex topology, called the 'algebraic topology' (also known as the finest locally convex topology), by declaring that any convex set $C$ such that $int(C) = C$ is open." Why is this a topology? The union of two convex sets is not necessarily convex, so the collection might not be closed under arbitrary unions. By the way, $int(C)$ denotes the set of 'algebraic' interior points.
That is, $c \in C$ is an algebraic interior point if for every $v \in V$, there is a $t \in (0,1]$ such that $(1-t)c + tv \in C$.
@user193319 I doubt I can help you finish, but could it be that the author means that this collection of convex sets is a basis for the topology?
It's possible. Let me see if things work out with this assumption.
13:28
i didn't expect that "algebraic" can modify not only "topology" the subfield of mathematics, but also "topology" the collection of sets...
so algebraic topology does not study algebraic topologies...
@user193319 From Encyclopedia of Mathematics https://encyclopediaofmath.org/wiki/Locally_convex_topology :
$\textbf{Locally convex Topology}$
A (not necessarily Hausdorff) topology $ \tau $ on a real or complex topological vector space $ E $ that has a basis consisting of convex sets and is such that the linear operations in $ E $ are continuous with respect to $ \tau $. A locally convex topology $ \tau $ on a vector space $ E $ is defined analytically by a family of semi-norms (cf. Semi-norm) $ \{ {p _ \alpha } : {\alpha \in A } \} $ as the topology with basis of neighbourhoods of zero con
 
2 hours later…
16:03
A construction believed to be asymptotic to Sqrt[8*n]*Log[Sqrt[8*n]]^2 : pastebin.com/w2zvPAry
That would bound the Tjebytjoff psi function if it could be proven.
That would probably bound the Tjebytjoff psi function.
@LeakyNun I want to ask a question related to Socialism.
what do I know about socialism
You can.
16:32
@LeakyNun This is too much
In Communism they say the capital will be distributed equally, so what I think do they pay equal salary to everyone? For example equal salary of General manager and an employee?
Or even if we consider the 19th century world, did Communist countries use to pay equal salaries to Lieutenant and an artillery officer?
@LeakyNun Oh sorry! I meant to write “Sociology” but wrote “socialism”.
and still what do I know about sociology
@BalarkaSen people playing 4d chess, this guy playing 5d chess
:(
No problem, bye.
@Knight What are the communist countries of 19th century man
@BalarkaSen I meant the early ideas of Communism not the modern one where Capitalism is a little-bit allowed (like today’s China)
16:47
There were no communist countries in 19th century bro
Idea was followed.
what about the holy roman empire tho
@Thorgott lmao
Roman? Empire?
I don’t like war :(
Russia, Poland and few others did follow Communist ideas.
USSR is 1917. That's 20th century not 19th century haha
16:51
I never used the term USSR.
I simply said Russia
Russia wasn't a communist country before USSR lmao
What are you smoking
Give me that stuff
It was. Ideas were followed.
That's not what a communist country means LMFAO
@BalarkaSen Nothing.
16:52
@BalarkaSen Didn’t get you.
ROFL
@FadedGiant I will not mention the name of the author and the book, but he hated and wrote many things against communism.
And even Leo Tolstoy mentioned in Anna Karenina the way workers were in 1870s
I don’t know if it was 1870s or something else.
:D
There were revolutionary ideas brewing in the late 19th century in Russia of course. And of course communism as an ideology was established in the 19th century by Marx, and the Paris commune happened during that time
There was no such thing as a communist country in 19th century
To be strict here, there were no countries before the nationalism movement.
Napoleon Bonaparte made many annexions and all the borders and rulers were destroyed.
@CalvinKhor This might be a tremendous coincidence but somebody with the same name taught me calculus at university :o
17:09
@Khallil sup m8
17:20
@BalarkaSen certainly not, you had people such as Proudhon and Fourier and Owen long before, and their ideas still have sway amongst various people who call themselves the c-word (often more than Marx I'd guess)
yeah i shouldnt have said it was established by Marx
i dont know about Fourier too much, actually. was he a moderate?
utopian
dostoyevsky bashes him in Demons lmfao
gotcha
Charles Fourier, =/= Joseph Fourier of course
very different fouriers
both nerds
yeah I know
Joseph took part in French revolution
17:23
he was also quite portly
lmao yeah chubby af
he ran the heat equation over himself
Joseph was a friendo of Napoleon too
Napoleon had too many math friends.
@CalvinKhor Yo! This was about 5 years ago now but it's cool to see somebody I (possibly) know on math.se :p
Off-topic. Let $f : M_1 \to M_0$ be a local diffeo and $g : M_2 \to M_0$ be a smooth map. Then the projection $M_1 \times_{M_0} M_2 \to M_2$ is a local diffeo.?
inb4 math is off topic
2
@robjohn yes
17:29
What does the notation $\times_{M_{0}}$ mean?
fiber product
Its the pullback of $M_1 \to M_0 \leftarrow M_2$.
@feynhat Yeah man this follows either by looking in charts or writing down the derivative
@feynhat Nobody knows what this means dork
man... I don't even know what are the charts on the fiber product. we proved its manifoldness using transversality so I never bothered to construct an explicit atlas.
@MikeMiller wut.
@feynhat The maps are f and g obviously.
@Khallil 5 years ago....maybe analysis III.......? also thats some good memory lol
What is the dimension of the fiber product? The fiber product is just the inverse image of the diagonal in M_0 x M_0 under the map f x g : M_1 x M_2 -> M_0 x M_0. The diagonal has codim m_0. So the fiber product should have dim m_1 + m_2 - m_0.
17:43
You do too many things abstractly
@feynhat Which is clearly m_2 if $f$ is a local diffeo
oh of course.
@CalvinKhor Oh it was Differentiation but you mentioning Analysis III tells me that it's the same person haha
The tangent space to a point $(p_1, p_2) \in M_1 \times_{M_0} M_2$ is going to be $T_{p_1} M_1 \times_{T_{f(p_1)} M_0} T_{p_2} M_2$, and because $T_{p_1} M_1 \to T_{f(p_1)} M_0$ is an isomorphism this fiber product of vector spaces projects isomorphically to the second factor
ahhh i didn't think Differentiation would be called calculus @Khallil
@MikeMiller cool.
18:33
I'm not entirely sure what the thing could be classified under, @CalvinKhor :b
Maybe one of the circles of hell?
@Khallil Are you calling beautiful mathematics circles of hell?
@TedShifrin IIRC, I had the pleasure of teaching @Khallil what a Fréchet derivative was for a map between Banach spaces a full year before the supposed first functional analysis class
Well, better than Univ Chicago's crazy honors course where they learn functional analysis and never learn a decent amount of multivariable calculus/analysis at all. But I digress.
im not sure anyone other than me came out of that knowing what a Banach space was
Maybe you still don't know :P
18:43
Hi all
@TedShifrin I'm pretty sure that the course was in retaliation to a previous syllabus that spat out students like that (ergo me) :P
I am back once more with a question
@Calvin: A proper multivariable calculus course (such as mine), even though it's just in $\Bbb R^n$, should give you all the tools for stuff in Banach spaces without a problem.
Hello, @CharlieShuffler.
provided we have some random variable $X$ following e.g. a lognormal distribution, what properties must a function $f$ then have to ensure that the random variable $f(X)$ still has a valid density function?
If the question is not well-formulated please let me know
I feel as if I am missing something obvious
What is a valid density function?
18:46
@TedShifrin that is correct, i think the main benefit was the higher order derivative was easy since k-linear maps also form banach spaces
valid density function being one that is positive everywhere and integrates to one
Yeah, sometimes trying to do things in ultimate generality is just bad, bad pedagogy, @Calvin.
@CalvinKhor Oh we had the definition of a Banach space from a metric spaces course so it was all good for me
but that course was entirely too much too early
In general the function of a random variable doesn't even have to be a nonnegative random variable, @Charlie.
You are correct
I wanted to not go into too many complicated details
18:50
@CharlieShuffler $f$ just needs to be measurable? so basically anything goes?
but $f$ is defined as something of the form $f(b) = \int^b_a 1/g(x) dx$ with $g$ strictly positive and continuously differentiable
@CalvinKhor Could you elaborate? I am not too confident on those topics
when you say density function, does it have to be...a function
I mean, $f(X)$ has to admit a valid density, i.e. one that is positive everywhere and integrates to one
Why?
That's not usual.
(That's the one I remembered from studying stuff like this ^)
18:56
so say, f=0 is ruled out because its density is a dirac mass at 0
@TedShifrin Because in financial applications this is a construct for ensuring there is no arbitrage (ignoring calender arbitrage)
OK, so you have to make this explicit in your definition.
@CalvinKhor Yes, also because $f$ is of the form $f(b) = \int^b_a 1/g(x) dx$
That's not usual for a random variable.
Its I suppose part of the definition of "Valid"
18:57
@TedShifrin I must say I was also under the impression that those two constraints must always hold
@CharlieShuffler the uniform probability on [0,1]'s density function is the indicator of [0,1] which is not everywhere postive
The probability density is different from the function of the random variable itself.
I thought a probability density is called valid when it's non-negative, measurable and integrates to 1 over $\mathbb{R}$.
@CharlieShuffler no, not you too
you are saying something distinct from @Khallil
x≥0 vs x>0
I will resign from this particular conversation.
Heya @robjohn
lol good choice @TedShifrin
you mean because I specifically said "positive"?
everywhere positive, in fact
19:00
I'm everywhere neutral :b
Ok, I apologise, but I am used to there being a difference between positive and strictly positive
i.e. positive also means zero
but my mistake then
also you said function, which rules out measures that are not absolutely continuous wrt lebesgue
I figure I am in over my head here
I did not formulate my question properly from the beginning
Apologies
You should see half the questions I asked on here back in the day
robjohn and Ted sensei must've been punching their keyboards
My idea was that if I left out most of the details I would not confuse anyone, but instead it led to more confusion
19:04
best to throw everything in there to rule out pathological examples and stuff
Right, I'll keep it in mind for the future
Thanks anyway everyone
@TedShifrin Just btw if you @Charlie you get me not @CharlieShuffler :P
the amount of times I wrote @ Mike and didn't get Mike Miller was outstanding
speak of the devil :o
presumably f is 0 outside of [a,b], as a function on [a,b], its $C^1$ and increasing, so $P(f(X) \in [c,d] ) = P(X \in [f^{-1}(c) , f^{-1}(d)])$ which you can write as some integral which should eventually lead to what you want @CharlieShuffler
@CalvinKhor Thanks very much, I will get into it immediately
19:12
i kinda like positive/strictly positive instead of non-negative/positive because i hate 'non-positive' but im not gonna change what i say lol
Hah fair enough
i dont wanna confuse anyone who learned it the way i did :P
I think your hint led me to the answer, thanks alot @CalvinKhor
@CharlieShuffler excellent!
nonpositive
nonpositive is a great word
immediately gives you a mental image
@TedShifrin hey ted!
20:29
(removed)
Anonymous
Is there any simple way to argue that $S = \{(m, n) : m,n \in \omega + 1\}$ with dictionary ordering has ordinality $\omega^2 + 1$?
Anonymous
Do I have to show that $(\omega + 1) \times (\omega + 1) = \omega^2 + 1$?
Finding elements for multiplicative group
1
Q: Multiplication group for $\mathbb Z_n$ modulo $n$

user1787812By definition: Let $\mathbb Z^+_n = \{[0],[1],[2],\ldots,[n−1]\}$ $\mathbb Z^+_4 = \{[0],[1],[2],[3]\},$ but how $\mathbb Z^*_{12}$ is $\{[1],[5],[7],[11]\}$ ?

Bit confused with this definition here
Is a holomorphic function in the disk, continuous on the boundary, determined by the values on the boundary?
Yes! Thanks to the maximum principle
20:48
I thought it was one of those Cauchy integral theorems that proved that
How does your maximum principle argument go?
Well, turns out I need it for a meromorphic function
(@Thorgott if it was holomorphic then the difference between two such functions would have a maximum in the closed disk which must be on the boundary, so it is everywhere zero)
ah, nice
But for a meromorphic function I'm not sure it works
Oh yea I remember seeing that maximum principle proof
Another way to do it for a holomorphic $f \colon U \to \mathbb{C}$, where $D \subset U$ is a closed disk containing $a \in U$, is to take an arbitrarily small $D$ and bound above the difference between $$ \left| f(a) - \dfrac{1}{2\pi i} \int_{\partial D} \dfrac{f(z)}{z-a} \text{ d}z \right|. $$
20:58
Yes, but this suppposes that we are holomorphic in a neighborhood of the disk
You can take a big circle inside the unit disk and let it go to the unit circle from inside
No problem
Let $f$ be a meromorphic function in the unit disk that is zero on the boundary and continuous in the closed disk (as a function to the Riemann sphere). Does it follow that $f$ is identically zero?
Is the residue theorem useful here?
Not that I see
If the function is not surjective then we are done: choose a value $a$ not in the image of the function, then consider $1/(f(z)-a)$.
What if it's surjective?
21:15
Can it even be surjective?
Surely it can't (unless I'm tripping in which case please absolutely call me out)
I'm not saying it can, but why couldn't it be?
Oh wait stereographic projection
I don't know if there exists a surjective example
Can't you just take $1/f$ where $f$ is some lacunary function
Like $f(z) = \sum z^{2^n}$
Can I?
21:28
I don't know I am asking
That seems to be mero in the interior of the unit disk, and is largely zero on the unit circle; continuity at boundary might be an issue
It is not continuous at 1
it has a singularity there
how do you see that
all roots of unities are of course singularities of $f$. I am taking $1/f$
Why does that not extend to the boundary continuously at 1?
Oh, I take it back
Ok, since it turns out to be not quick I'll post it in a question
21:34
Oh I guess you want meromorphic, so no essential singularities
my guy has one at $0$
0
Q: Is a meromorphic function determined by its boundary values?

EmolgaLet $f: \mathbb D \to \widehat {\mathbb{C}}$ be a meromorphic function inside the unit disk. Assume that $f$ is zero on the boundary and continuous in the closed disk (as a function into $\widehat {\mathbb{C}}$). Is $f$ necessarily identically zero? If $f$ is not surjective then we can take $a\...

Posted
Hi, a @Balarka
Hi @Ted
Really? but it is the inverse of a holomophic function at 0
so it is a pole
Ah nevermind me yes
I'm smoking something
Anyway I don't know if it's obvious that $1/f$ extends to the boundary continuously
if it does it has to be zero everywhere on the boundary, of course
21:37
What happens if you use Blaschke factors to clear out all the poles and make the function meromorphic?
You can have infinitely many poles Ted
Accumulating at the boundary
just first thought
I guess you really can't because of continuity
Not if it's continuous to the boundary.
But Blaschke just moves points around in the disk
So what do you mean?
poles are isolated
21:40
@Thorgott not for functions on the interior of the unit disk
isolated is not a problem with accumulating to the boundary. Continuity probably is.
here it's also continuous on the bd
Oh, maybe I didn't even need to bother with that. I didn't want to mess up the boundary value condition, but multiplying by $\prod (z-a_j)^{\mu_j}$ won't mess it up.
thats why
Oh, cool
21:41
I just walked in :P
I think you solved it, Ted
yeah once it has finitely many poles you're through
I used to write comprehensive exams in complex analysis ... but I am rusty.
last time I knew, poles of meromorphic functions were isolated by definition
Yes, but if you're meromorphic only on the OPEN unit disk ...
They can accumulate to a point on the boundary, in principle.
Think of points marching to infinity in the half-plane.
21:44
yeah, of course, not debating that
Well, our function is only mero on the open disk.
So what are you debating?
I posted your answer in the post. Thank you!
Glad I could help, @Emolga.
What's a short argument that the poles can't accumulate to bd because of continuity
Doesn't the function have to be close to $0$ in a neighborhood of any boundary point?
21:49
oh ok it's also zero on all of the boundary
Just continuous would suffice, though, I think.
Oh, continuous and finite-valued on the boundary.
yeah I don't see an easy argument
but his guy is a map from closed disk to CP^1 no
I added finite-valued.
it's continuous on the closed disk, so if the poles were to accumulate, they would have a limit point, which cannot itself be a pole, but a sequence of poles accumulating to a finite value would contradict continuity (arranged poles as sequence and for each pole pick a point with distance <1/n from the pole and absolute value >n)
Ted's solved it by now, right?
21:51
@Thorgott: I think Balarka is still thinking of just continuity to the Riemann sphere. So it could take the value $\infty$ at the limit point.
It has finitely many poles because they don't accumulate on the interior (definition of meromorphic) and not to the boundary (it's zero on the boundary)
Yeah, we agree on that.
Can a continuous map $f : \overline{D} \to \Bbb{CP}^1$ which is holomorphic on the interior have accumulating poles to the boundary
Irrelevant to the question at hand, right?
21:52
urgh, why would you consider that
Balarka is intellectually curious.
Different question
No I'm just dumb tonight
Yeah I dunno
I would bet that's ok but i don't know
So we can just as well make it about holomorphic functions and zeroes.
Something like a weighted sum of poles at $1-2^{-i}$
21:53
And then I don't see any contradiction at all.
yeah something like this should work
What do you mean, ocntradiction?
Pretty sure it works
(I actually saw exactly this once)
In the original question, there's a polynomial $p(z)$ so that $p(z)f$ is holomorphic on the unit disc, continuous up to the boundary, zero on the boundary. So $|p(z)f|^2$ is harmonic, zero on the boundary, hence zero.
The function can certainly be continuous on the boundary and be zero at a limit point of zeroes. So our function could have poles accumulating at a point on the boundary which maps to $\infty\in\Bbb P^1$.
21:56
So we're done. Not sure what the debate is about
There wasnt any debate Mike
why do you always look for debates
I guess you can skip that and just use the maximum principle for $|pf|^2$
It's just not a very clearly written chat man I can't tell what you people are talking about
I was just entertaining Balarka's embellishment of the question. It was reasonable.
i was just asking, i dont have to ask to ask
its written up there man
Chill, everyone.
21:58
I'm not unchill, I'm just saying I couldn't follow the course of discussion.
Time to go teach, see ya
Yeah, I walked in in the middle of it all, too.
i was just having a banter
Misha Millerovsky, always looking for debates in friendly conversations, right out of Dostoyevsky's Demons @MikeMiller
For the first time in my MSE experience, there are two people asking a plethora elementary differentiable manifolds questions without, apparently, the basic background. I'm just avoiding commenting or answering these two people now.
I've experienced this sort of thing with other fields, of course, before.

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