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12:00
No idea about usage of CN.
ADG
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$$\frac1{1+x^3}=\frac1{(x+1)(x+\omega)(x+\omega^2)}$$
then use:
or use complex methods
@user223679 pinged
What is complex methods?
Methods that are complex.
2
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Residue theorem
@WillHunting good one.
@WillHunting were you here all this time?
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12:03
Cauchy-Goursat theorem
@WillHunting Knvm
Cauchy's integarl formula
Never used that.
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@user223679 easiest one:
$$\frac1{1+x^3}=\frac1{(1+x)(x^2-x+1)}=\frac A{1+x}+\frac{Bx+C}{x^2-x+1}$$
Now use $Bx+C=D(2x-1)+E$
@Incurrence Are you here?
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then it would be:
Hey @Chris'ssis.
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12:07
$$A\ln|1+x|+D\ln|x^2-x+1|+E\frac1{\sqrt{3/4}}\arctan\frac{(x-1/2)}{\sqrt{3/4}}$$
@user223679
@WillHunting
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Here i have found that:
$A=1/3$
$D=-1/6$
$E=1$
@ADG Isn't this the partial fraction method?
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@user223679 just what i told ya
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12:10
$B=-1/3$
$C=2/3$
@user223679 aur main pehle kya keh raha tha?
Complex method and Partial fraction method is same?
And what is Cauchy's formula then?
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@user223679 no that was my first attempt, (forget it)
@ADG you think engineering wont be rote ? :D you should chat with seniors in college ;)
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for i'm going for cs
@ADG Whats the difference between Cauchy Formula, Residue Theorem, Complex Method and Partial fraction Method?
12:15
@WillHunting Hey. How is it going?
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@user223679 All but the last DNE (my short form for DoesnotExist; got it from LCD (my short form for LimitContinuityDiffrentiability (froma allen)))
@user223679 you need to wiki search it , you learn it in first year college maths..
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@Chris'ssis willing to help this @user223679 with $\int\frac1{1+x^3}{\rm d}x$
@Gowtham in college, really, intersting.
@ADG hmm?
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@Gowtham nvm^2
12:17
@Gowtham I know about Cauchy Mean Value theorem. Is the same one?
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@user223679 no, just another great contribution from great cauchy
@user223679 you know what a complex number is , right ?
From what I think, Cauchy theorem is the same as Residue theorem which is same as the Partial fraction method.
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@user223679 a+ib $i:=\sqrt{-1}$
@Gowtham Yes.
12:21
so think of how you would form functions , plot graphs calculus with complex numbers .. those theorems do just that
@ADG Am I correct?
@ADG and then you might be willing to show me your way there.
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@Chris'ssis *not a native english speaker
@Chris'ssis neither me nor he gets what you said
2
Or not
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12:23
@Chris'ssis I don't know ${\rm Ti}_2$, but ${\rm Li}_2$
@ADG inverse tangent integral
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See this is how with some very intelligent people that solve some super complex problem and just ask others to shadow others.
@Chris'ssis IDK
@Gowtham since your method has been starred by atleast 2 people (other than you since you can't) it really must be true.
BYE
It's been an insanely long time since I've actually done some actual math out of interest. Geez, I gotta quit this bad habit and get back into the groove. Heya peeps, howz ya'll been?
math.stackexchange.com/questions/1219409/… and math.stackexchange.com/questions/459996/… have been plagiarised @BalarkaSen by Remember Me. I flagged.
12:36
plagiarized?
Hello @WillHunting
Long time, no see....
@WillHunting If your accusation is true, It's somewhat hilarious that the user's name is "Remember me" but as @Balarka points out, what's your proof?
@WillHunting Yes, he should provide sources to those materials. What I'd do is put the info in quote block and say [link] says this.
@BalarkaSen I am totally shocked that he would do this...
12:39
@WillHunting k.
@BalarkaSen And as you know, he openly passed off the first one as his if you read the transcript in that room. That is how I found out.
right.
@WillHunting When I was 13, I would plagiarize [copy-paste] a lot of stuff on Yahoo Answers including general views on life, the universe and everything. It's nothing to be shocked about. It's just immature.
4
@Nick This is a different matter.
@BalarkaSen I am not going to talk to him again.
@evinda Aha!
@WillHunting How is it going?
12:42
@BalarkaSen I have finally had enough of his nonsense. This is the last straw.
@evinda Not good. =(
Why? :( @WillHunting
@evinda You don't know? My mental illness, which I always talk about, a bit too much, in this chat.
@WillHunting I don't see how. What the lad has done is point the questioner to the answer he seeks. Serve him a notice in the comments to link the sources and make him understand that respect has to be given to the original author.
@WillHunting Dude, you're a very tough nut even if you got a bit of loosy-goosy in your noggin.
12:44
Yes, I thought that you would be better, since you don't visit the chat many times anymore.. @WillHunting
i never really plagiarized anything. i wrote a few answers with which i was helped by a few people around here (even recently on symmetric products), but didn't write word-by-word what others said.
@evinda Oh, I see. Hehe, I just did not want to talk too much non math, hehe.
I see... @WillHunting
Have you reached any of your goals?
@evinda Not really, I am still struggling.
@WillHunting Do you tinker again with maths now?
12:47
@WillHunting From what I understand, he's only copy-pasted some stuff without crediting the source. What else is there? Sure, it's plagiarism. Something we frown upon but it's nothing to take personally. Carry forward the formality. Serve a notice. Be done with it.
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@Nick I was banned 3 months for plagirsiing, see
@ADG Well, you should have credited the source. It serves you right. Although 3 months seems heavy. 1 month seems better.
@Nick If you read the transcript carefully, it is a clear case of passing off as his own.
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@Nick I had one month but when i came back I posted 5 answers and forgot that i plagiarised in 1 (only) of them. I had no notice (don't know why) but got another sus (surely bad).
@WillHunting Then he's just being evil. In which case ban him for a month, if he repeats it, ban him for 3 months and then if he does it again, then for life.
12:51
@Nick And all this while we were trying to help him with math...
@ADG You DESERVED a notice. That was a clear hindsight on the part of the mods.
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I don't like this ban thingy, In my case, it never helped me improve my mistake. rather make me avoid the site.
Mew
Mew
it's not about rehabilitation
@WillHunting If he's anything like 13 year old me. Then, he's a "fixer-upper" (in constant need of help). Don't help the help vampire. You'll only regret it.
Mew
Mew
it's about stopping you from plagerizing for 3 months
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12:53
@Nick recently (aftre the next 2 yrs) I got a warning for rudeness and advertising area 51 proposal in comments (separately) and i said something in chat and got one for a year, it ins't practical. It just means I don't need to use this site.
Mew
Mew
the ban is necessary to deter other users from behaving badly
@ADG Sometimes presentation and context matter a lot. In life and even on the internet.
Mew
Mew
when other users see that you or another user has been banned, it helps stop them from misbehaving
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@Nick It was not on MSe btw.
@Mew Don't take this personally but I hate that thought. It's that kind of thinking that chops rapists heads off rather than their private parts.
12:55
@BalarkaSen I am very shocked...
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@Nick anyways on MSE I just got a message few years back on saying that "stupid reverse 1100 and you get 11?" (something like)
@WillHunting i am not shocked, but merely surprised.
@BalarkaSen I really won't talk to him again...
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BYE
Mew
Mew
@Nick, there is no logical reason for revenge
12:56
@WillHunting I'd make a joke about the word "shocked" in relation to mental health but I respect you too much to make it.
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@ACuriousMind the physics huy "yay i am being mentioned, so i'm making a difference?"
Mew
Mew
@Nick, but a deterrent does lead to increased productivity and legal behaviour
@Nick No need to respect me, I am just a sick man.
PSA: Please only flag messages that are actually offensive.
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*english level neyond the understandability of non-native users
@ACuriousMind I don't get what is the difference between the two you mention?
12:57
@WillHunting Every good man deserves respect, in sickness and in health.
@ACuriousMind What was flagged?
@Mew No, I wasn't talking about revenge. I was talking about taking away the privilege a person misuses. And Life is a right, not a privilege.
@ADG What are you talking about?
@ADG Take a lesson from Buddha, "Take what you can understand. Discard what you cannot."
@WillHunting About 10 messages of which only one was evidently mildly insulting, some could be construed to be insulting in context, and some weren't insulting at all.
13:03
@ACuriousMind I think I know which convo that was.
Too much negativity in this room. Let me flow into somewhere more zen. Toodles :)
Imagine the following situation: you manage to solve an open problem, then share the problem with someone, and that someone spread it further and then someone else is about to publish something based upon your work. Then, you're told "Ah, I don't even remember you sent me that result", the kind of thing that not even an Alzheimer patient would forget.
This is what would terribly annoy me in terms of plagiarism.
To tell you the truth, if I were a mathematician and had any kind of inclinations to plagiarism, I'd be out in the second second and get another job.
When you look at mathematics as if it was an art there is no sense to ever think of plagiarism.
1
Q: Backward Euler method- How do we get the approximation?

evindaApproximating $y'(t^n)$ at the relation $y'(t^n)=f(t^n,y(t^n))$ with the difference quotient $\left[\frac{y(t^{n+1})-y(t^n)}{h} \right]$ we get to the Euler method. Approximating the same derivative with the quotient $\left[\frac{y(t^{n})-y(t^{n-1})}{h} \right]$ we get to the backward Euler meth...

I haven't understood how we get the formula
$$y'(t^n) \approx \frac{y(t^n)-y(t^{n-1})}{h}$$
Do you have an idea?
13:20
One of the things to achieve in terms of mathematics in the long run is to avoid any kind of strong contact with mathematicians that do not see mathematics as an art. As long as I do it, mathematics remains an art to me.
(I'm not in business with mathematics)
Mew
Mew
I use maths to earn a living
Maths is a tool for achieving productivity
I'm not talking about people (no matter who), it's useless to do that, but I talk about attitudes, ideas that I do not agree.
There is no greater satsifactions than getting amazing results being totally fair in all you do.
Mew
Mew
good point
laterz
user96977
13:37
if f^r is the probability of a bent coin coming up heads r times, and (1-f)^(N-r) is the probability of it coming up tails in the rest of N tosses, what is the meaning/significance of the product (f^r)(1-f)^(N-r) ?
13:48
6
A: Is the site being too lenient in helping people with homework?

quidWhether or not a question is homework or not, is not a major concern of mine. It is typically quite difficult to determine, and in those cases where it is more or less obvious the question is normally lacking for other reasons, too (see below). What is a concern of mine is the quality of questio...

@DanielFischer No, it is not. Other sites are being too strict regarding homework.
@Balarka: OK then, congrats.
user96977
i agree, there is mathoverflow .etc
@Nick As quid says, what's relevant is not (so much) whether it's homework, the quality of the questions is important.
@DanielFischer I understand, the usefulness to the public is a main factor in hw-type questions. Other sites are very strict about this but MSE also cares about people.
13:53
Morning, @DanielF.
@MikeMiller Happy diurnal isomorphism.
user96977
if f^r is the probability of obtaining r heads when tossing a bent coin, and (1-f)^(N-r) is the probability of obtaining tails on the other throws, why is the probability distribution f^r*(1-f)^(N-r)
Unrelatedly, happy diurinal isomorphism @DanielF
@MikeMiller What would I need two urinals for?
smacks @Mike good night
13:57
Hola @Ted.
Hola, @DanielF :)
That's not my business, @DanielF.
@DanielFischer I'd like to share a bad question which is actually interesting
-3
Q: How Many Days Until 100 Screens

AnthonyIf one screen costs 200.00 and every day you make 2.00 from one screen. How many days until you have 100 screens if you buy a screen every time you get 200.00?

Let us assume that you initially have $200.00$ units which you use to buy a screen. Let us also assume that a screen need to run for an entire day inorder to make $2.00$ units.

Starting from the $1^\text{st}$ day, this screen makes $2.00$ units per day and after $100$ days you can buy your $2^\text{nd}$ screen.

Starting from the $101^\text{st}$ day, you'll have two screens which make $4.00$ units per day and in another $50$ days, you can buy your $3^\text{rd}$.

Starting from the $151^\text{st}$ day, you'll have three screens which make $6.00$ units per day and in another $\dfrac{200}3$ d
Maybe it's the ambiguity but it's just wonderful at first glance.
@Nick Find out what the OP is actually asking, and make it a good question. As is, it's useless, since too many things are left to guessing.
14:15
@DanielFischer I guess your right. I will, surely.
14:48
Does anyone know of a theorem that is something like: if the derivative of a function is never $0$ at all points on an interval, then the function is a diffeomorphism
The function might have to be $C^1$ maybe, I don't know the exact conditions
mr eyeglasses
Hi @TedShifrin
@ᴇʏᴇs The inverse function theorem says that such a thing is a local diffeomorphism. It's rarely a diffeomorphism: what about $e^x$?
You should be able to prove that if $f'>0$ on an interval, then $f$ is increasing on that interval. You also should know a theorem called Darboux's Theorem that even without assuming $f'$ is continuous, if $f$ is differentiable, then $f'$ has the intermediate value property (i.e., it cannot change sign without going through $0$).
@Mike: I'm pretty sure he meant on an interval and to its image
and in $\Bbb R$
ok, then we're happy
I know $\Bbb R$ was meant
14:50
But we do not need $C^1$.
you awake at 6 AM preparing for your evening lecture, @MikeM?
It's 8, @Ted, and I finished yesterday
It's 8 AM now ... but you showed up hours ago.
Hmm... just one, I think
LOL, probably so.
At my age, time is fluid.
Better than gaseous.
14:57
You do have your share of bathroom humor this morning ... :D
I'll debase myself once a year or so
15:10
I left my notes at home... ****
Oh oh ... time for a walk.
You're not supposed to be that forgetful when you're just of age.
It sucks so bad when you commute like an hour to school and you forget stuff at home..happened to me once with a calc lab report
I've had students bring me homeworks later in the day or the next morning because they forget them. And these aren't the students who just hadn't started :)
I hope I won't have to commute to grad school..I know one student in my class who got accepted to the Grad Center here but he didn't get any stipend or fellowship or TA duties..just free tuition
user96977
is the standard deviation just the square root of the variance?
15:27
yes, @TruthSerum.
user96977
thanks
@ᴇʏᴇs One should never go to grad school unless one has funding to do so. An admission without full funding is a soft rejection.
user96977
15:39
If a function has infinite support, does that mean that it is non-zero everywhere
Define infinite support.
user96977
iff it is non-zero everywhere?
user96977
that is the question
If you don't know what infinite support means, why do you care about it?
I suspect you have a definition given in a course or something, and this is a homework problem. I want you to find the first definition and look carefully at it. If that's not the case, and you're just asking what infinite support means for some reason, that's not what it means.
user96977
why do people here always suspect
user96977
15:51
i suspect that once you took a course and were given a definition or something
user96977
it is of interest to me because it is used as a categorization for different probability distributions, so it is obviously a fundemental characteristic: en.wikipedia.org/wiki/List_of_probability_distributions
user96977
@MikeMiller here is my revised question: given that supp(f) (the support of f) is defined to be the set of points where f(x)!=0, what does it mean for a function to have /infinite support/?
@MikeMiller I am not sure why $Z(\subset)$ is the coevaluation map $\Bbb C \to X \otimes \overline{X}$, though. ($\subset$ is the (0+1)-bordism between the empty manifold and $S^0$)
user96977
@BalarkaSen if you are not sure why, why do you care about it?
'Cause I want to compute with TQFTs, not just know some fancy words.
I want to make sure that I am sure about it :)
user96977
16:00
well that's a very honourable reason. would you be so good as to explain, w.r.t my definition of support, the meaning of "infinite support" ? (or "finite support", i believe i am intelligent enough to deduce one from the other)
@TruthSerum: First of all, support is defined to be the closure of the set of points where $f$ is nonzero. One talks about compact support or noncompact support.
sorry : i don't think i have the time just right now. i am trying to figure out what's happening with these TQFTs.
and hi @Balarka. Get to work.
get to what work? :P
user96977
ok, well it's obviously too complicated, i'll remove any mention of "support" from my notes, since i can't get to the bottom of it. and anyway, it's just a category for discrete probability distributions, not distributions in general
16:04
oh, well, giving the context would have helped. Then it means that there are infinitely many outcomes with nonzero probability.
Asking only half the question here really is a pain in the ass to us.
user96977
ok thanks
@Ted I am taking a break from lin alg right now. Well, more like I am making a digression and learning these so-called "TQFT"s.
Skimming, more like.
I guess I'm going to start doing lin alg again soon.
user96977
@TedShifrin how does this make the distribution graphs different?
user96977
can i inspect a graph and see if it has infinite/finite support?
How do you graph a probability density function with infinitely many nonzero values?
@Balarka: You don't need permission from me :P
16:12
In the continuous case it's easy :)
user96977
@TedShifrin how about a small interval :(
I kind of feel guilty for reading Lurie's notes, @Ted, thus the message. :P
But it's a discrete random variable ... not a continuous random variable. What do you mean by a small interval?
user96977
1/x has infinite non-zero values
user96977
but i can graph it and learn a lot from the graph alone
16:14
But that's function with an interval for a domain and an interval for its range. A discrete random variable takes on only a countable number of nonzero values.
user96977
can't you "graph" a function only defined at discrete points?
Infinitely many?
You can only graph finitely much of it.
user96977
an interval, say $[a,b]$ with $a,b \in \Bbb Z$
A typical discrete random variable would have a PDF like $f(n)=1/2^n$ for $n=1,2,3,\dots$.
And it sums to 1 and everything!
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16:18
@Nick hope you understand
I agree other sites are too strict, therefor MSE is the only site which renders the most useful to me.
user96977
@TedShifrin does that distribution have a name?
Well, sure, @pjs36. I paid careful attention :P
I don't know one, @Truth.
user96977
ok, i hoped that it might
I'd assume some kind of "geometric [something]", as it's a geometric sequence
user96977
i only know one distribution, the Binomial distribution
16:20
So a prof. decided to hold classes in the room I usually study in, so now I have to find a new study spot...
user96977
@pjs36 when you say "it's a geometric sequence" do you mean E[X], with X following that distribution, is a sequence?
The typical geometric random variable has a probability density like $p(1-p)^k$, @pjs36.
mr eyeglasses, ordinarily classrooms are meant for classes :P
I just meant the sequence $\{2^{-n}: n = 1, 2, \ldots\}$ is a geometric sequence, that's all. But @TedShifrin is right, like always!!
@pjs36 ... I only know this because I taught probability last fall.
user96977
ok, if you were to sum a sequence where the n'th term is given by $1/2^n$. seems like an irrelevant thing to say
16:23
@TedShifrin The entire semester this classroom was empty :(
We have no empty classrooms at all during the days, mr eyeglasses ... We used to.
That's why students go to the library, mr eyeglasses.
@TedShifrin I quit going to the library because you have to walk around and wait for an empty seat to open up
Also the library is literally on the opposite side of campus where I have classes
hey @iwriteonbananas
hey balarka
hi bananas ... office review hours ... bubye
16:28
hey ted
bye ted
why are you reviewing offices?
probability theory is annoying
i second that
once im done w this problem, im gonna check out luries first vid
that's cool
I'm trying to understand this question.. if $\lim\limits{x \to \infty} f(x) = \infty$, then does $f(x) = 1$ have solutions? But $f(x) = 1$ doesn't go to $\infty$ as $x \to \infty$ even though $f(x) = 1$ by itself has solutions..so the question doesn't make sense to me
@ᴇʏᴇs depends on what $f$ is.
16:38
@BalarkaSen $f(x) = 1$
I can think of situations with infinitely many (exponential and sine thrown together), finitely many (polynomial), or 0 solutions to $f(x) = 1$ with $f(x) \to \infty$
Oh I thought the question meant that $f$ is the constant function $1$
@iwriteonbananas, statistics is worse. How does one keep track of these chi-squared and t distributions with their endless jargon?
Well, if $f(x)$ were identically $1$, written $f(x) \equiv 1$, that seems incompatible with an infinite limit, so I assumed it was talking about solutions to $f(x) = 1$.
@user96343 i second that
16:47
Hello!! Is someone of you familiar with recursive functions and primitive recursive functions??
growls at bananas
growls at apples
:P
@BalarkaSen: That's the definition of the coevaluation map, no?
@MikeMiller erm. well, he says $Z(\supset)$ is the evaluation map, and i thought $X \otimes \bar{X} \to \Bbb C$ defined by $(x, f) \mapsto f(x)$ was the definition of the evaluation map.
and it's not obvious to me how these two coincide.
in particular, i don't see how the map $Z(\null) \to Z(pt^+ \; pt-) \to Z(\null)$ given by splitting up the circle into two bits is the linear map which multiplies a complex number by $\dim X$.
17:04
I don't understand the question. Considering $M \times I$ as a map $\varnothing \to M \sqcup \overline M$, $Z$ takes this to what's called the coevaluation map. Similarly it sends $M \sqcup \overline M \to \varnothing$ to what's called the evaluation map. They don't coincide. A
blah, \emptyset
Are you asking why their composition is the identity on $k$?
I think it is. I don't remember.
Oh, no it's not.
it's not.
it's multiplication by dim X
So I don't know what you're asking.
and i don't see how he gets that.
17:05
Where is this written?
@MikeMiller no, i thought the definition of the evaluation map was $(x, \sigma) \mapsto \sigma(x)$. i don't see why one would get this map when one applies $Z$ to the bordism $ pt \sqcup \bar{pt} \to \null$
or is that not the definition?
I don't know where you got that idea. He defines the evaluation map to be what I said above.
1.1,7(b)
I don't even know what $(x,\sigma) \mapsto \sigma(x)$ means in this context.
it's the map $X \otimes \bar{X} \to \Bbb C$ given by picking an element of $X$, picking a map $X \to \Bbb C$ (an element of $\bar X$) and evaluating the chosen map at the picked element.
@MikeMiller ok, now i don't see why $Z(S^1)$ is $\dim X$.
(Z is a 1-dimensional tqft, S^1 is considered to be a bordism between the empty manifolds and itself)
You're identifying $Z(\overline X)$ with $X^*$, the dual space (or else your evaluation map doesn't make sense). The point is that what we call the evaluation map in the cobordism category defines such an isomorphism $Z(\overline X) \to X^*$. That's why the two notions of evaluation maps agree.
i understand that Z(\bar M) is M^* (i gave you a proof above), but not why that should mean that Z applied to M \sqcup \bar M \to \null has to be the evaluation map.
17:12
I don't have time to do this. You need to think carefully about what's going on for yourself.
Hey @robjohn!!!
Could you take a look at my question?
1
Q: system of First-Order ODES

evindaI am looking at the following exercise: Consider the initial value problem $\left\{\begin{matrix} x''(t)=x(t)\\ x(0)=a\\ x'(0)=b \end{matrix}\right.$ Write it as a system of First-Order ODES with suitable initial values and show that Euler method can get unstable for a great step $(h)$. Tha...

ok, no prob. i guess i am missing something obvious.
user96977
user96977
what is this identity called? it's listed here en.wikipedia.org/wiki/Event_(probability_theory)
17:36
@Balarka: Think about it more generally. I have two vector spaces $X, Y$ and a perfect pairing $X \otimes Y \to k$. You saw that this defines an isomorphism $Y \to X^*$. Show that, after following this isomorphis, the original pairing becomes what you call the evaluation map.
There's no topology going on after you show that the pairing is perfect. It's all down to linear algebra.
But the point is that the "evaluation map" you started with defined this pairing, and therefore defined this isomorphism, and therefore after the isomorphism is the evaluation map.
17:52
@TruthSerum Have you taken calculus? If $F(t)$ is a cdf, then it's the antiderivative of a pdf, say, $f(t)$. Then by the fundamental theorem of calculus, we have $\int_u^v f(t)\ dt = F(v) - F(u)$; it's just how integrals are evaluated, I'm not sure it has a name.
Because if $F(t)$ is the cdf corresponding to the pdf $f(t)$, then we have $F'(t) = f(t)$, hence the FToC gets used.
@TruthSerum In some circles, it's called "Albert's identity".
user96977
thanks. yeh, i was wondering how the random variable X is related to an "event" in the probability sense as a set of outcomes
18:16
@Chris'ssis Do you think you could have finished the exam in 4 hours ?
18:43
Hello @DanielFischer !! Could you take a look at my question: math.stackexchange.com/questions/1258178/… ?
@LeGrandDODOM This kind of exam is like that: all the problems are elementary, that's clear, all seems related to classical results, nothing new, so you either know the stuff or not, it doesn work with half a measure, and then some of the points might require some pendantic explanations that might take some time to put it well.
@LeGrandDODOM I don't know if I finished in 4 hours, but I had ideas for all points almost instantaneously. I mean putting all your thoughts carefully on page might take time. I'm definitely not the one able to write fast and well at the same time when dealing with such amount of stuff. I might make mistakes, return to them, correct them and so on.

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