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r9m
12:01 AM
@DanielFischer Thank you :) .. I'm sorry if I pestered you (again) :-(
 
@r9m Hey, I asked you to, didn't I?
 
@DanielFischer There's something I am missing.
 
@KajHansen I think I have a more clever way: every sector covers an angle 2pi/n, and if the angle of the vector is alpha, than the sector it is in is floor((n*alpha)/(2*pi))
 
r9m
@DanielFischer and I exploited that generous liberty .. :] thank you :)
 
@PedroTamaroff Both are easy. How do you deduce continuity from the closedness of the graph?
 
12:06 AM
@DanielFischer Hm, let me do the other one first. Suppose the mapping is continuous, and that $(x_n,tx_n)$ converges to some point $(x,y)$. Then $x_n\to x$; so $tx_n\to tx$ by continuity, but $tx_n\to y$, so $y=tx$ and $(x,tx)$ is on the graph.
 
@KajHansen and then I just need some compensation since atan2 returns a value between -pi and pi, and I'd rather have a value relative to north (I need to determine the sector several points on a map are in, relative to another point)
 
I cannot see where OMT hops in.
Maybe I should use that $(x,x)$ is closed in $X\times X$.
 
@PedroTamaroff Yes (since I assume you're treating only Fréchet spaces, otherwise, sequences might not be sufficient). The OMT hops in for the other direction, closed graph implies continuous.
 
@DanielFischer Yes, that's what I suspected.
Now, suppose that the graph is closed.
 
Yes. What else do you know about the graph?
 
12:09 AM
It is complete?
 
@PedroTamaroff Right. And?
 
I don't know.
I am not sure if I should show say that $\lVert t\rVert<+\infty$.
 
$\Gamma(t) = \{ (x,tx) : x\in X\}$
 
Yes.
That is the image of $X\times X$ under $(1,t)$.
 
Forget $X\times X$.
 
12:13 AM
OK.,
 
Since $t$ is linear, $\Gamma(t)$ is - what?
 
It is a subspace of $X\times Y$.
 
I suppose by subspace you mean "linear subspace", do you?
 
Good.
 
12:14 AM
@Hippa, @Kaj et al: OK, I'm done.
 
So, it is a closed linear subspace of $X\times Y$, hence, it is?
 
I said it was complete, I did.
 
@PedroTamaroff And a complete linear subspace of a Fréchet space is?
Or Banach, if you want.
 
I don't know, also Banach?
 
Yesss.
So, if we find a continuous bijection between that and another Banach/Fréchet space ...
 
12:20 AM
I am not sure if I am following, but I was thinking $\bar t:X\to\Gamma(X)$ with $x\to (x,tx)$, I am not sure if that helps.
.
.
 
Hi
I have this integral problem; Is there anyone can help me to solve it?
\begin{align}\label{eq:er8}
ps=\int\limits_{0}^{\infty}\frac{e^{-b~z}}{\sqrt{z}} \Big(\frac{\beta}{\beta+z}\Big)\Big(\frac{\beta+z}{z}\Big)^L e^{\frac{\eta}{z}}\Gamma\left({1-L},\left(\frac{\beta+z}{z}\right)\left(\frac{\delta+z}{\alpha}\right)\right)~dz,
\end{align}


where $\alpha$, $\beta$, $\eta$, $\delta$, and $b$ are real numbers larger than zero. $L=0,1,2,...$
 
Why are you posting the same thing twice?
@DanielFischer probably gave up on me. =P
 
@PedroTamaroff That's a bijection between the graph and another B/F space. But we don't know yet whether it is continuous. But, we know something related that is continuous.
 
sorry I tried to edit it
 
@PedroTamaroff Nah. I'm just trying to answer a question on main in parallel.
 
12:24 AM
@DanielFischer Projections? Diagonal maps?
 
@pedro do you think I post question here is better or asking a question in the main board?
 
Projections sounds good, @Pedro.
 
@barznjy That kind of question is better for main.
 
@pedro ok I will post it now. Thanks
 
@DanielFischer And projections are open.
 
12:27 AM
They are?
 
Oh, wait.
Closed?
 
@PedroTamaroff From the product space, not necessarily from all subspaces thereof.
 
Oh, they are. I was thinking closed.
 
@DanielFischer Ah, OK.
 
Sowwee ...
 
12:28 AM
Still continuous.
 
But, @Pedro, the restriction of the projections to all subspaces is still continuous.
 
Yes, yes.
 
Do you see it now, @Pedro?
 
So I have a continuous, surjective linear map from Banach spaces.
 
@PedroTamaroff Even bijective, and that's not entirely irrelevant here.
 
12:30 AM
@DanielFischer OK. I'll continue alone now.
 
@PedroTamaroff Good. And when you're done, you may look at the proof in some book.
 
12:41 AM
@DanielFischer Dang. I think I'm stuck again. Now I know $t(X)$ is complete.
 
@TedShifrin, just saw your solution. That's pretty cool.
 
@PedroTamaroff That's astonishing, it need not be.
Try the other projection first, maybe.
 
I have $\pi_1:\Gamma(t)\to X$, then $t=\pi_2\pi_1^{-1}$.
I'm done.
 
What is SE coming to? Don't people, you know, read the help center/guidelines when they make an account?

http://math.stackexchange.com/questions/843082/first-order-logic-for-it-job-openings
 
The question is what this really means, @Kaj :)
No, no one reads that. To be honest, I didn't.
 
12:47 AM
It looks like something potentially not math related and a homework assignment at the same time.
 
@PedroTamaroff Yup.
 
@KajHansen You need to keep your voice off your nose.
 
@PedroTamaroff, I get that a lot. If I could, I would :)
 
That's what my singing prof. says to me all the time.
 
@TedShifrin, I finally read them a couple months in. I think it gave me a badge for it too :P
And by "read", I of course mean skimmed.
 
12:49 AM
I think I might have a few months in, @Kaj.
Your nose meets your larynx? @Pedro
 
@TedShifrin WAT
 
LOL
 
I think your aphorism makes more sense in Spanish.
 
off = away.
 
I wonder what non-native speakers think about how idiomatic English can be. Some stuff must make no sense at all when it's first encountered.
 
12:53 AM
Probably. I have long since forgotten.
 
Much of it still makes no sense to me, @Kaj.
 
Are you a native English speaker @Ted? I feel like I should know this, haha
 
Yeah, and yeah you should :)
 
@PedroTamaroff, is that matrix problem homework for you?
 
@KajHansen No, it is not something compulsory.
I can solve it if I want to. I don't need to hand it in.
 
1:02 AM
Wow, that was a long nap.
 
@MikeMiller Was it The Big Sleep?
 
No, I'm still corporeal.
 
1:17 AM
Hi @Karl
 
I think I just solved the four-parameter recurrence $g(2n+j) = 3g(n) + \beta_j + \gamma n$, where $j = 0,1$, $m \ge 1$, and $g(1) = \alpha$. This is exercise 1.16 in Knuth's Concrete Mathematics. I'm not 100% sure I got it right; if someone is familiar with the "repertoire method," I'd greatly appreciate someone checking my work here.
Hi @TedShifrin!
 
Huh... I got booted from the room
@Chris'ssis sorry... I was not back when I expected. I answered a question, but I need to leave again for a meeting. Life is busy the last two weeks.
 
1:34 AM
Hi @anorton @robjohn
 
@robjohn That's happened to me before.
 
@TedShifrin hey there...
@MikeMiller what, real life intruding on the net? the nerve!
 
the booting from the room, but that too :P
no text, but occasionally I'll notice my chat window is back in the list of different rooms
 
Hello @Ted
I got a chance to play tennis earlier today.
 
2:03 AM
hmm
I could study at home or I could study on the way to getting coffee
but I cannot decide between the two options
 
2:39 AM
A little confused....what's the difference between Mathematics.SE and MathOverflow?
 
@Tutor MathOverflow is for professional mathematicians to ask each other questions about research in math
 
3:10 AM
@MikeMiller And Mathematics is just about math?
 
3:27 AM
hello o/
 
@Tutor Yup, of all levels.
 
@MikeMiller Aha. Thanks for clearing that up! :)
 
3:53 AM
If $F(x) = f(x\2)^2 + g(x\2)^2$ where $f'(x)=-f(x)$ and $g(x) = f'(x)$, $F(5) \neq 5$, right?
oops
$F(x) = f(x/2)^2 + g(x/2)^2$*
 
4:22 AM
anyone here?
 
you're alone in a cold world
any appearance otherwise is an illusion
 
4:45 AM
still here? @blue
 
mmhmm
 
well, only in an illusory sense
 
indeed
 
5:09 AM
I had a question but answered it...
I have another
Say a topological space $X$ has cardinality $\kappa$. How many pairwise nonhomemorphic subspaces can $X$ have?
I think the answer should be $\kappa$
by the way, I just saw Grand Budapest Hotel, a wonderful movie
 
 
1 hour later…
6:19 AM
Hi
 
6:29 AM
@Meysam Hi
You look cute! @Meysam
 
@Sawarnik thank you :)
I need to get a quick question answered
How to minimize Aλ-λb where b is a n x 1 vector and A is a n x n matrix?
 
6:50 AM
@Meysam what kind of thing is λ?
doesn't seem like Aλ-λb makes much sense
 
7:07 AM
is $\lambda$ an eigenvalue?
@Meysam
 
I think λ is the variable
but the expression Aλ-λb doesn't make sense - λ could be a scalar, or a vector, or a matrix, and it still wouldn't make any sense
 
@blue are you good at topology?
 
7:27 AM
none of us are good at anything
 
liar
 
7:50 AM
He's a good liar ;-)
 
do you do topology?
@skullpatrol
 
doing it on rubber sheets
 
I am only a banana.
 
Greetings
 
how is your series book coming along
 
7:55 AM
Greetings my friend.
 
@robjohn OK. No more need for e-mail, I'm going to post the results here after I publish them in AMM (American monthly magazine).
@skullpatrol Helllooo!!! How are you doing? :-)
 
Fine thanks, how are you @chrissis?
 
@skullpatrol hehe, thanks! Pretty fine! :-)
 
how do you find out if a series is unsolved?
 
That's it.
 
8:17 AM
Suppose $X$ is a topological space and $Z\subseteq X$ is the zero set of $f\in C(X)$. Why would $f \restriction X\setminus Z$ have an inverse?
nonsense
oh I guess they mean $^{-1}$ to be $1/...$ lol
not inverse
funny stuff
 
 
2 hours later…
10:47 AM
@Chris'ssis okay. Sorry I've been out so much this weekend.
 
11:07 AM
... eerie silence ...
 
Hi
Does $\frac {\infty}{e^{\infty}}$ tends to zero?why?
@robjohn ^
@DanielFischer Sorry for calling you :D
 
@MrWho Do you mean $\frac{x}{e^x}$? $\frac\infty{e^\infty}$ doesn't mean anything.
 
@MrWho $\frac{\infty}{e^\infty}$ makes no sense by itself. I guess you got it from a limit? Which?
Morning, @robjohn.
 
@DanielFischer good morning, to you, too :-)
 
@N3buchadnezzar what software pack did you use to write that book in PDF (using latex)?
 
11:20 AM
@robjohn @DanielFischer I mean $\frac {x}{e^x}$ but the x tends to infinity, that's the part of calculating the gamma function integral , the guy says $\frac {x}{e^x}$ when x goes to infinity is zero!
 
@MrWho $\displaystyle\lim_{x\to\infty}\frac{x}{e^x}=0$
 
[Edited]
@robjohn Well should we consider $UV$ 0 to inf part of the integration by part a limit?
 
@MrWho I don't understand what you are saying... perhaps some context would help.
 
@robjohn Yeah, I'm trying to show it in latex
@robjohn I can't show boundaries with bracket in latex :( consider x as the answer of integral how can I represent the boundaries after the bracket $ x]$
 
@Chris'ssis Yeah latex
 
11:28 AM
@MrWho You mean like $$\int_1^2\frac1{x^2}\,\mathrm{d}x=\left[-\frac1x\right]_1^2$$
 
@robjohn Yeah, got it
@robjohn Is that a limit? $\frac {x}{e^x}]_{0}^{\infty}$ ?
:(
 
@N3buchadnezzar MikTeX? Anyway, I'll solve this problem immediately.
 
@robjohn You fixed it?
 
@MrWho yes.
 
@robjohn Thanks, so now, is that a limit?
 
11:33 AM
@Chris'ssis Whether you use MikTex or TexLive is irrelevant, it's just the distribution. I use MikTex, as I was not able to install TexLive. To write things i use TexMaker, has a few missing features, but overall it is decent.
 
@MrWho anytime you see $\infty$, a limit is intended. There is no real number $\infty$, it means a limit to as large a number as you want.
 
@N3buchadnezzar Perfect. Thanks. :-)
 
@robjohn So if it was from 0 to 10 it would be considered a simple manipulation not limit, but now because it has infinity the limit is intended?
 
@MrWho so $\displaystyle\left.\frac x{e^x}\right]_0^\infty\equiv\left(\lim_{x\to\infty}\frac x{e^x}\right)-\frac0{e^0}$
 
Does someone know inverses of polynomials in formal power series ring ? It appears here math.stackexchange.com/a/843364/66096 but I can't figure out
 
11:37 AM
$\displaystyle\left.\frac x{e^x}\right]_0^{10}\equiv\frac{10}{e^{10}}-\frac0{e^0}$
 
@robjohn Uhum, clarified, thanks :)
 
@N3buchadnezzar it works great! :-)
 
@G.T.R There, Did is talking about reciprocals, not inverses as in inverse functions.
 
@N3buchadnezzar Great! Thank you! :D
 
11:46 AM
You know, just ask if anything =)
I really love the way i refer to equations and theorems in my document
"Please see equation (4.4)" And equation (4.4) is a hyperlink, but only 4.4 is colored.
 
@N3buchadnezzar LaTeX Error: File `microtype.sty' not found.
LaTeX Error: File `a.sty' not found.
 
You sure you installed everything properly? :p
Also this is just my main document, to get anything to run you need all the other files as well.
 
@N3buchadnezzar Nothing will be a paper and a pen :)
 
@MrWho ?
 
@N3buchadnezzar I'll fix that immediately.
 
11:52 AM
@N3buchadnezzar I prefer writing stuff by my own that using latex for everyday notes :)
 
@MrWho Well this is not everyday stuff :p
 
Lol someone posted an edit and comment is "Just for the excavator badge xDD"
 
@N3buchadnezzar You math major? :-)
 
@MrWho undergrad
 
@N3buchadnezzar Any official paper of yours?
 
12:01 PM
@MrWho Nothing offical :p Been droodling on this for about one and a half year, on and off.
 
@N3buchadnezzar Whose book is that? yours ?
 
@Chris'ssis: I don't think I've seen Ovidiu's book
 
@MrWho So far just a collection of notes and ideas, but it's mine 100% yeah.
 
@Chris'ssis depending on the file I am processing, I've had to grab some latex support files from the net.
 
@robjohn I know. I just made an update for a package. Everything is fine now.
 
12:10 PM
@robjohn MikTex does that automatically
 
@N3buchadnezzar Seriously, it's a masterpiece, looks like underground math book :-)
@N3buchadnezzar Why didn't you write it in English? :(
 
Dunno, might rewrite it sometime. But it is hard to balance a social life, being a undergrad and working on a document
 
@N3buchadnezzar Everything looks so beautiful. However, I want my characters to be more black-pronounced.
Well, I'll fix that soon.
 
@N3buchadnezzar You should have written it in English at first, man, English can be understood by most of the people, but German(!) , just what the H !
3
 
\hypersetup{
colorlinks=true,
pdfmenubar=false,
pdfstartview={FitH},
linktoc=all,
urlcolor=blue,
linkcolor={},
}

\usepackage[nameinlink]{cleveref}

\crefformat{equation}{#2equation~(#1)#3}
\Crefformat{equation}{#2Equation~(#1)#3}
This should work
 
12:23 PM
But to write well in English, you need to "think" in English.
 
@N3buchadnezzar Thanks :-)
 
Then you would do something like
"\ begin{equation} 2 + 2 = 5 \label{eq:something} \ end{equation}
\Cref{eq:something} is a good equation "
 
why is $\Gamma (n) = (n-1)!$ true? today I'm just getting goosebumps dealing with Gamma style functions!
 
@MrWho How many languages do you know?
 
@N3buchadnezzar 2 languages :-D
 
12:26 PM
@MrWho Look at propostion 3.2.1 on page 85.
 
@N3buchadnezzar I see, I can understand the notations but explanation ...
 
Well its basically integration by parts, you want to prove that $\Gamma(s+1) = s \Gamma(s)$
 
@N3buchadnezzar I've proven that.
 
@MrWho Then $\Gamma(s) = (s-1) \Gamma(s-1)$ right?
 
Yeah
 
12:29 PM
@MrWho Thus induction
 
@Alizter I've got bad problem with induction, I'm an intuitionist !
 
So $\Gamma(s) = s(s-1)\Gamma(s-1) = s(s-1)(s-2)\Gamma(s-2) = s(s-1)\cdots 2\cdot (1) \Gamma(0)$
 
facepalm
@MrWho You can't just have a bad problem with induction. Then you cannot prove things!
@MrWho Intuition is great for finding things but how are you going to prove them?
 
@Alizter You can prove by induction that it is hard to prove anything without induction.
 
@N3buchadnezzar You can also prove that things can only be proved by induction.
 
12:32 PM
Induction is not my cup of coffee.
 
@MrWho You can't just avoid it though! It is important.
 
Thats not right. It is like saying you do not like water in any form :p
 
I remember not really seeing the point but once you do you will realise it's strength.
 
@Alizter I've already realized its strength, but it's just not really tangible.
 
@MrWho STill gamma is unclear?
 
12:37 PM
@N3buchadnezzar No, i got it, but I'm checking to see what's the value of $\Gamma (0)$.
 
@MrWho There is no value...
 
@MrWho You need to check Gamma(1), I made a mistake
 
@N3buchadnezzar Oh , yeah, I see, I was saying to myself, damn, it can't be integrated :)
@Alizter What
?
 
@MrWho If I told you to prove that $\sum^n_{k=1}k=\frac{n(n+1)}2$ could you?
 
Well, yeah
 
12:38 PM
@MrWho How would you do it?
 
@MrWho But induction is one of the devices that mathematicians use to turn coffee into theorems ;-)
 
http://warwickmaths.org/files/gamma.pdf is decent, is roughly based on PMA by Rudin, and a book fittingly called "The gamma function". Rudin is a bit on the skimpy side, and The gamma function is very throughout, but like Rudin does not cover a lot of depth.
I also really liked this essay written on the history on the gamma function,
http://www.jstor.org/stable/2309786. Seems both Rudin and the other book took much inspiration from this essay.
 
1, 2,3,4,5,6, ..., n - I start from both end and starting point, so I sum the n/2 times of n+1
 
@MrWho What?
 
@skullpatrol LoL, yeah, believe me or not, I'm not a philosopher, but induction ...
 
12:42 PM
1 + 2 + 3
3 + 2 + 1
4 + 4 + 4
 
@Alizter n+1, 2 + (n-1) , 3 + (n-2) and ...
@N3buchadnezzar Yeah
 
1 + 2 + 3 = \frac{4 + 4 + 4}{2} = \frac{3 \cdot 4}{2}
 
@MrWho What about for n^2?
 
@Alizter What do you want to say?
 
Forget it. You don't like induction. You miss out.
 
12:45 PM
@Alizter That's how you answer?if you're not willing to say what you want to say, don't try.
 
@MrWho No. You seemed stubborn so I stepped away.
 
@Alizter Why stubborn? I thought you want to say something, so say it!
 
Can you prove the formula for $\sum^n k^2$?
 
@Alizter Yes.
 
@MrWho With or without induction?
 
12:49 PM
@Alizter I probably prove it with complex functions.
 
28
Q: Examples of mathematical induction

Michael HardyWhat are the best examples of mathematical induction available at the secondary-school level---totally elementary---that do not involve expressions of the form $\bullet+\cdots\cdots\cdots+\bullet$ where the number of terms depends on $n$ and you're doing induction on $n$?

 
$$\huge{\huge{\huge{:(}}}$$
 
@MrWho What would these complex functions be
 
He who doesn't believe in induction is severely handicapping his chances of success.
 
A maths teacher says to the class that during the year he'll give a surprise exam, so the students need be prepared the entire year. One student starts thinking though:

1. The teacher can't wait until the last day of school, because then the exam won't unexpected. So it can't be the last day.
2. Since we've removed the last day from the list of possible days, the same logic applies to the day before the last day.
3. By applying 1) and 2) we remove all the days from the list of possible days.
4. So, it turns out that the teacher can't give a surprise exam at all.
 
12:51 PM
@N3buchadnezzar Cool !
 
@MrWho Come on! Which functions?
 
@Alizter Let me see.
 
@N3buchadnezzar How do you write your name under the title, something like "by N3buchadnezzar"?
I can do it in some way but it doesn't work the way I want.
 
@MrWho Another student, who doesn't believe in induction, prepares everyday expecting that a test will be given on that day. Unfortunately he burns himself out and must drop the class.
 
@Chris'ssis Isn't it "\author{}"?
 
12:56 PM
@skullpatrol Well, that's my life story except dropping it :)
 
@Alizter yeah, but it doesn't appear centred under the title...
@Alizter Got that! All is perfect now!
 
$$\huge{\huge{:(}}$$
 
@Chris'ssis You can do it more advanced using a titlepage, but \author usually works.
I see now I forgot to put in my own name anywhere in the document :p
 
@N3buchadnezzar :D
 

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