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05:00
its like a major achievement to pull off a stunt like this, really
getting an album full of purely offensive material out there and get it to chart in itunes
it's beautiful
crosses fingers
@MatheinBoulomenos awesome yeah thanks a lot I already like it a lot
been reading first chapter is very nice :D
I like number theory already
@MatheinBoulomenos so I think I like number theory, complex analysis, and geometry
@Corellian I also like some songs from Pink Season unironically. "Rice Balls" is one.
Honestly Pink Guy made better music than joji
@BalarkaSen classy :P
05:13
@BalarkaSen same. it's a banger
i dont really follow joji so dunno. but i wish him all the success
same, same
its a B O P
at least he's psychologically in a better place being joji
imho his best talent is his natural comedic finesse, but he considers youtube a side job so whatevs
well he's stopped making content on FilthyFrankTV
he has made a official statement that he's not going to continue making that stuff
like a month ago
05:18
oh yea? i mean his life/career his choice. the fanbase can be really caustic either way. i can imagine the outrage
a major part of the fanbase is cancerous, yeah. but he's developed a lot of illness lately
mostly neurological ones
ironic, but true
damn that sucks
you can't go to rehab for neurosis
i know he's mentioned epilepsy and some kind of mental dysfunction a long time ago
05:26
Alright, so the pentagonal dihedral group acts on a 5-tiled mobius strip
namely on the set of all variously colored bands
90% of anything is trash
remember that
does D_n always have the form {identity, r, r^2, ... ,r^n; s, sr, sr^2, ..., sr^n}? where r is a rotation between adjacent vertices and s is reflection
yup it does
When a function shows up in the next star wars movie and saves the day, it will be a surface of revolution.
@AkivaWeinberger i topped your joke
05:30
cool
so the general method is counting possible configurations in each conjugacy class and then shoving it in some formula I can't recall
is it burnside?
yup looks like it. we're using orbits under the group action
 
2 hours later…
07:56
@TedShifrin Morning Ted
Or maybe its night time for you :D
 
1 hour later…
09:06
@TobiasKildetoft Hello
@Jacksoja Hi
@TobiasKildetoft @Jacksoja Hey :D
Hello Kasmir
@skullpatrol Hello Skull!
What Courses are you doing ? :)
09:27
@KasmirKhaan what courses are you doing? if you dont mind me asking
helo
what courses are you taking @Shobhit ?
Hi, what courses are you taking? @Tuki
@tuki in this semester - complex analysis, topology, measure theory, numerical analysis, mathematical programming
calc 2 and some programming courses
the programming course i have right now is not that interesting but the calc 2 is
mathematical programming ?
@Shobhit which year are you in? Sounds very similar to the courses I had last year
09:32
1st year MSc.
would be 1st bachelor studies or some of the courses might be aimed for 2nd year but i don't study for degree right now
actually trying to apply for computer science program
@AlessandroCodenotti you?
meanwhile taking some separate courses from the uni
then i can later on include them in my degree when i get accepted
does this make sense to you ?
@tuki do whatever interests you, then work will feel like play
yes exactly
you study in the us or somewhere else @Shobhit ?
09:38
india
you?
Finland
do you have to pay for studies in india ?
is there like fee for semester ?
yes, ofcourse
dont you?
yes it is free in finland
you have to pay sometimes for books etc.. but attending school / uni is free
@Tuki Don't you get paid to study?
well most students get their funding from goverment
and some take student loan on top of that since the amount isn't that large that they give you
09:40
oh, how nice
but we are talking about living expenses right now
also 44% of the student loan is automatically free if you complete your studies in time
44% of it is basically free money
damn, finland sounds nice
rest of it you have to pay back
and the interest rate in the loan is very small compared to other loans for example your default bank loan
another thing how hard it is to get accepted to uni in india @Shobhit ?
how many people apply and how many get accepted ?
what kind of ratio in this
the uni i am in is a part of 12-15 uni, they take entrance exam, top 300 are selected and are distributed with respect to rank in these uni's.
if you apply here, the exam is not hard, you can crack it.
entrance exam probably includes some mathematics ?
09:45
but i'd advise not to come here
yes, mathematics ofcourse
they do all science courses
yes pretty much same here
We have this system here that if you don't get accepted they put you in reservation slot
so if someone does get accepted but they reject the offer by themselves then the spot will go to someone that is highest ranking in the reservation slot's
reservation means a whole different thing here
same here
i was in 4th reservation slot last year to number 1 ranking uni here
so the acceptance wasn't that far
I'll hopefully crack the exam next time and tbh it's not that hard after all.
09:51
atb :)'
anyway you mentioned numerical analysis and mathematical programming
@tubi about the question that you posted on lagrange multipliers, i am getting different values of $x,y, \lambda$. Are you sure they are right?
aren't they the same thing ?
no i am not
i used default calculator so it's highly likely that i miss typed some numbers ^^
maybe should have used matlab for example
09:54
check this
still one negative and two positive
== indefinite
i'll continue, i was just checking values
damn, that hessian matrix, its a lot of work to check that
we have on a lot of these courses the policy not use calculators in exams etc.. so i usually try to solve the problem as far as i can without any external aid
yes it is
calculus dont need calculators, numerical analysis does
If you know alternative ways to determine the critical point type than hessian matrix ?
09:58
@Shobhit sorry was away
@KasmirKhaan :)
@tuki nope
am taking rep theory atm and some other analysis courses
But mainly focusing on representation theory since its the hardest :D
another thing is that is this solvable without calculator ?
Moimoi tuki :D
))
09:59
dont talk in finnish now because thats all what I can say :D
your from ?
represenatation theory, we dont have it here in our courses
india is very back in science studies
taking Courses in sweden atm
@Shobhit the problem is that india do have the ppl to do those Courses =p
i mean look at the big University, many indians there
"big uni"?
yeah, they may have the people, but they dont teach it
10:03
by big i meant, the good ones >< eg harvard =p
@Tuki i think your computation of hessian matrix is wrong
the indians there, they only have indian origin, very very less are actually from india that make it there.
that is the problem
if the country dont support research, many will have to leave to do theirs in USA or Uk ect
also the hessian should have one parameter more $\lambda$
sadly yes
$H(x,y,\lambda)$
10:07
whenever there are "maths monsters" here, like ted shrifin, balarka sen, eric silva to name a few, they take about things, i start googling them as i am reading, but the things they say i have never heard of them and i have searched the curriculum here, its not in the courses. Meaning i wont be able to talk like that, Ever (sad face)
@Tuki your hessian is wrong i think. Please check.
ok
Differential analysis stuff is still largely incomprehensible, though Balarka helped me to understand the poncaire hopf theorem.

Do india do manifold stuff at all?
well would it be possible for you to seek education elsewhere ? @Shobhit
@Secret manifolds is here in the course
@Tuki i have to do MSc here first
@Secret in which year are you?
I am not from india, and I am a chemistry PhD
10:13
wth
nice
so interested in mathematics? or studying? as in a degree
Mainly interested, the higher level maths I really have studied are linear algebra, some simple differential equations solving methods and multivariable calculus
and that is back in my 2nd year
All other maths are done by self study and learnt from the chat
nice
You might want to zoom down there in your graph, cause your x,y value of your critical point is approx (4000, 609) something
so the saddle point may be too small to see at the current scale
ok
also is this method suppose to work ?
is it ok to compute hessian from lagrange function ?
10:28
It appears the hessian of the lagrange function need to be handled more carefully, thus one cannot tell about minimas and maximas via the eigenvalues https://en.wikipedia.org/wiki/Hessian_matrix#Bordered_Hessian

Never encountered that before in my 2nd year course
so getting an indefinite hessian in your workings suggest at least your hessian is of the correct form, now you need to check whether the minors are -ve
the edge is actually smooth
From little bit closer
Hi chat!
What is the conclusion in this question
hello! @BAYMAX
Hi
3
Q: Increasing real valued function whose image set is connected

StrugglerLet $S = [0,1) \cup [2,3]$ and $f\colon S \rightarrow \mathbb R$ be such that $f(S)$ is connected . Which of the following are true: a) $f$ is discontinuous exactly at one point. b) $f$ is discontinuous exactly at two points. c) $f$ is discontinuous at infinite many points. d) $f$ is continou...

also if hessian becomes singular what does this mean ?
10:36
Also posted in Topology room
so bordered hessian cannot be either positive-definite or negative-definite
only possible outcome is indefinite
yeah, and you need to check whether the minors have the correct signs
determinants of upper left
meaning i need to have always $n \cdot n$ submatrix
or truncated matrix
So the trick is in computing determinants and not egeinvalues
I think so... I don't know until today that hessians of lagrange functions need to be handled in a different way. I also tried plotting the function with the lambda value you solved but find no stationary points in wolfram alpha
though the signs of the 3 principle minors I get are +1,-1,+1 thus it should suggest you have find a minimum to the lagrange function
also @Shobhit your wolfram computations seems to be incorrect since border conditions is $x+y-50000$ not $x+y-5000$ your missing one zero
also i think the correct answer would be that this critical point is maxima ?
10:49
are there functions $f : \Bbb R^2 \to \Bbb R$ for which the statement $\dfrac {\partial \partial f} {\partial x \partial y} = \dfrac {\partial \partial f} {\partial y \partial x}$ is well-defined and is false?
(@Secret)
hello, i have two sequence (a_n) and (y_n) uch that $a_n\to0$ and $y_n\to+\infty$ what can be the limit of the pruduct $a_ny_n$ ?
@Vrouvrou any number >= 0
it can be $+\infty$ or any $\alpha$ , is there an other case ?
oh, any number
is the limit can do not exist ?
10:51
@Vrouvrou then you don't call it a limit
1 min ago, by Vrouvrou
hello, i have two sequence (a_n) and (y_n) uch that $a_n\to0$ and $y_n\to+\infty$ what can be the limit of the pruduct $a_ny_n$ ?
"what can be the limit"
assumes a priori that it exists
@Tuki Uh, strangly, i get neither answers in WA by maximise nor minimise the original function:
wolframalpha.com/input/?i=miaximise+100x%5E(3%2F4)*y%5E(1%2F4)+subje‌​ct+to+x%2By%3D50000
wolframalpha.com/input/?i=minimise+100x%5E(3%2F4)*y%5E(1%2F4)+subjec‌​t+to+x%2By%3D50000
@LeakyNun I DON'T KNOW IF THE LIMIT OF THE PRUDUCT EXIST
nowhere did that (4000, 609) ish point pops out
@Tuki my mistake
@LeakyNun is this what you are looking for? en.wikipedia.org/wiki/…
10:53
@Vrouvrou It might not exist, and it can be anything if it does.
@LeakyNun The "Windmill saddle" above is one example where mixed derivatives exists but not equal
@Shobhit thanks
wolfram gives this for the hessian
wolframalpha.com/input/?i=hessian+matrix+100*x%5E(3%2F4)y%5E(1%2F4)%‌​2Bz*(x%2By-50000)
@Secret thanks
@LeakyNun welcome
10:54
most other examples have something to do with the denominator $x^2+y^2$ but I don't know the general case yet
meaning there is flaw in my hessian that i had in the post
@TobiasKildetoft what is the condition to obtain that the limit exist ?
please
You need $C^2$ functions for the mixed partial derivatives to be equal, that's called Schwarz's theorem I think
@Vrouvrou essentially something about how fast the sequences go towards whereever they are going
the actual hessian is $$H(x,y,\lambda) \begin{bmatrix} -\frac{75y^{1/4}}{4x^{5/4}} \end{bmatrix} & \frac{75}{4x^{1/4}y^{3/4}} & 1 \\ \frac{75}{4x^{1/4}y^{3/4}} & -\frac{75x^{3/4}}{4y^{7/4}} & 1 \\ 1 & 1 & 0 $$
10:58
use \{ and \} for { and } in latex @Tuki
For there to be a limit, you need the sequences $a_n$ and ${1}\over {y_n}$ to be of the same order
hmm ok
But that is not sufficient
how fast is going to infinity is too fast, cause one can imagine if $x_n$ decays slower (details unknown) than $y_n$ can grow, the product will blow up
I also suspect if $y_n$ diverges to infinty by blowing up, no amount of $x_n$ can force it finite
"blowup"? @secret
like $x_{n} = n$
11:02
uh, I mean a diverging sequence where $y_n \to \infty$ as $n \to \infty$
(cause another type of divergence is oscillation)
@TobiasKildetoft i have $(y_n)\subset \mathbb{R}^N$ such that $|y_n|\to+\infty$ and $a_n\to0$ that's what i know
then $y_{n} = n$ blows up to infinity, and $x_{n} = \frac{1}{n}$ boils down to zero and $x_{n}y_{n} =1 $
@Secret
ah right, that reduces to tobia's case
is there an exemple where $|a_n y_n|$ has no limit ?
@Vrouvrou just have it vary between 1 and 2
let $a_n = 1/n$ as usual
and make $a_n y_n$ go like 1,2,1,2,...
11:09
? i don't understand
$a_ny_n = \frac{e^n}{n}$ also works if you want the limit to blow up
so $y_n = 1,4,3,8,5,12,7,16,...$
Leaky's example is basically if the value of the product oscillates, then the limit does not exist
but i say $y_n\in\mathbb{R}^N$ and $|y_n|\to+\infty$
1 min ago, by Leaky Nun
so $y_n = 1,4,3,8,5,12,7,16,...$
it does go to $+\infty$
11:11
you can have something oscillate and go to infinity, for example:
@Secret not that one
that one doesn't go to infinity
uh, the screen is not large enough
how about $y_n = n \sin (\frac{1}{n})$
better illustration
yeah, that works too
@Secret that one still doesn't go to infinity
11:15
conclusion in general there is three cases
@LeakyNun oops you are right, x eventually dominates
leaky is just commenting that my example does not go to infinty. Your original conclusion about the 3 cases should be unaffected
@Secret three cases? finite limit, infinite limit and?
oscillatory bounded/unbounded
(which is also a limit that does not exist)
see leaky's for an illustration
11:24
ok
does anyone know how sylvester's criterion works ?
also how do you define 1by1 matrix determinant ?
1x1 is just the entry itself
ok
en.wikipedia.org/wiki/Sylvester%27s_criterion i think this is the same idea as in bordered hessian ?
probably except the bordered hessian need those principle minors to alternate in sign in some way
2
Q: Geometric meaning of minors

forumreaderThis is a bit silly question I found on another discussion forum. I know that determinants can be used to compute volumes of parallelepiped. I also know that determinants can be computed by linear combination of its minors. Is there any geometric meaning of minors or some proof/explanation why th...

mapping to subspaces...
11:40
determinant is zero when linear transformation cause all points to map to a single line right ?
@Tuki depends on the dimension of your space
in $\mathbb{R}^2$ or $\mathbb{R}^3$ ?
it's hard to imagine what happens in $\mathbb{R}^4$ geometrically
or more like $\mathbb{R}^n$ when $n>3$
because your statement is true iff the dimension of your space is not 1
hmm good point i didn't thought of this
12:07
0
Q: Julia set of $x_n = \frac{ x_{n-1}^2 - 1}{n}$

mickConsider the following iterations : $x_0 = z$ Where $z$ is complex. $x_n = \frac{ x_{n-1}^2 - 1}{n}$ It is well known that for real $z > 3$ the sequence grows double exponentially. It is known that for $z = 3$ the sequence grows linear ; in fact like $3,4,5,6,7,...$. In fact When considering...

 
1 hour later…
13:33
@AlessandroCodenotti Not really. It suffices to be $C^1$ and $\partial_x f$ and $\partial_y f$ to be differentiable as multivariable functions.
So the $C^2$ condition can in fact be weakened
(The proof's in Dieudonne; I worked through it at some point of time in my life but have forgotten it now. It's a elaborate mean value theorem)
@BalarkaSen That's different than $C^2$?
Oh, the $\partial f$s need not be continuous
Correct.
Ah, interesting
@AkivaWeinberger Wait, no, what? They are continuous.
That's what $C^1$ means
@TobiasKildetoft I was meaning to ask you about something in representation theory of finite groups ( I heard you teach such course) is that correct?
13:46
$D\partial_i f$ need not be continuous, in particular, $\partial^2_{xy} f$ and $\partial^2_{yx} f$ need not be continuous
@Jacksoja Well, I have taught the basics, as it was part of an introductory course on algebra in general
@TobiasKildetoft okay my questions aren't that involved , since this is the first week of the course
How did your enrichment visit from high school kids go?
@skullpatrol Me?
13:49
What is a representation, direct sum, ,and how much linear algebra should one assume to know ?
@Jacksoja I don't have that much time right now. For direct sums, you can check out my notes pure.au.dk/portal/da/persons/…
@TobiasKildetoft I understand , thanks anyway
@skullpatrol Those were not high schoolers, they were in 9'th and 10'th grade (so just before high school)
second time went well. First one went ok, but not as well as I had hoped
@BalarkaSen are you at all good with orientability?
I have a statement I seem to lack enough background on. "the characteristic foliation of a surface S is orientable if and only if the normal bundle of S is isomorphic to the quotient bundle $(TM/\xi)\vert_S$."
13:58
Hm. Does orientability of the foliation mean co-orientability?

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