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00:00 - 16:0016:00 - 00:00

4:00 PM
@mickep It's not anger you see, it's the mean of the square that you see :-)
 
I have yet to do that ugly $\alpha, \beta, \gamma,\delta$ problem.
It seems very hard.
 
Fixed point problem?
 
@TedShifrin Hey there. Is it as overcast there as it is here?
 
@robjohn thank you for the temporary answer nonetheless :) How did you read it?
 
@TedShifrin Yeah, but it's easy though. $f : \Bbb R^n \to \Bbb R^n$ be cont. and define $x_k = f(x_{k-1})$, where $x_0$ is arbitrary. If $x_k$ converges to $a$, then $f(a) = a$. You just have to use that a sequence can't converge to two different things at once.
But I like it.
 
4:02 PM
@robjohn I added as much of a bounty as I could
 
@Balarka! Oh, totally easy ...
 
Sure.
 
@robjohn, totally fresh and clear here ...
 
@Anush I originally thought that the matrix had elements from $[0,1]$. The braces were too flat. I noticed the braces on the vectors because you mentioned the probability of $2^{-n}$. After I wrote my answer, I looked back at the question and noticed that the elements of the matrix were also from $\{0,1\}$
@TedShifrin odd... SD is usually more overcast than LA, being against the ocean whereas LA is surrounded by mountains. Perhaps the mountains are holding the marine layer in.
 
Hello@Ted@Balarka
 
4:05 PM
hi
 
@robjohn: You missed my update. I'm up at Stanford on my roadtrip trek.
hi @Remember
 
@robjohn I suppose in that case the probability of being equal is 0, right?
 
@Anush I don't know if it has something to do with the newer MathJax, or with the fonts on my new laptop, but the braces are much harder to see as braces.
 
@robjohn that's a shame
@robjohn I have no idea at all how to approach my question so even half baked ideas are welcome at this point :)
and there is a 250 point bounty!
 
@Anush well, as I mentioned, I noticed the braces for the vectors so I knew there was a $2^{-n}$ probability arising from the vectors being equal, but thinking that the matrices had real entries, I thought that the probability that they had a non-zero null vector in $\{-1,0,1\}^n$ was $0$.
@TedShifrin Ah... so you've passed through LA?
 
4:09 PM
@robjohn Haha, the mean of the square. I hope I'll remember that in the future...
 
@mickep yes. I created this avatar due to a comment made a long time ago.
 
oh, that is a while ago, I didn't know this chat was logged...
 
@robjohn: i'm stopping on the return trip, as previously discussed.
 
@robjohn to be honest, I am not sure what sort of mathematician would find my question interesting. Maybe an expert in probabilistic combinatorics?
do such people use math.se ?
 
@TedShifrin which places are you visiting?
 
4:16 PM
I don't think you can search for highest rated people with pairs of tags can you?
 
out of curiosity, i mean
 
Various friends around the SF area, then driving down the coast and LA, Balarka
 
sounds cool. have fun!
 
Well this is a weird question to ask here but since I have to give a talk on photo chemical smog I am asking anyways:
Can we say stuff about smog by thinking on the lines of Brownian motion?
 
@Anush give it some time. Someone may see it, especially now that it has a bounty.
 
4:20 PM
@Balarka Were you able to find the fault in your false argument ? Just asking out of curiosity since everyone was indulged in it
 
it was not my argument anyway, but yeah.
Mike found it.
 
Nice.
 
@TedShifrin Yes, I know you are stopping on Sep 11. How could I forget that? Just noting that you have been through LA
 
4:45 PM
@robjohn will do
 
5:04 PM
@MikeMiller Actually, I take back what I said. My space is homotopy equivalent to $K(G, n) \wedge K(G, m)$, the reason I wrote down above works just fine. But yeah, to prove that it's $(m+n-1)$-connected, the hint you gave is needed : $K(G, n) \wedge K(G, m)$ has no cells below $m+n$ dimensions. Thanks!
 
5:18 PM
What is $e^{-2ln(\sqrt{q})}$?
How does the -2 affect the answer?
"simplification"
Is it just $-2 \sqrt(q)$?
 
@Owatch $e^{-2\log(\sqrt{q})}= e^{-\log(q)}=\frac1q$
 
How.
$e^{ln(4)}$ is 4
How did the square root get eliminated?
or removed?
 
@Owatch What is $\log\left(\sqrt{x}\right)$?
 
I don't know.
 
$\frac12\log(x)$
$\log\left(x^a\right)=a\log(x)$
 
5:23 PM
Alright...
I see
You moved the power $\frac{1}{2}$ in front of $log(q)$, which made it $\frac{-2}{2}$, or just $-1$.
But I don't see why this didn't become -q?
 
@Owatch $e^{-\log(x)}=1/e^{\log(x)}=1/x$
 
oh
Well.. .
Alright, and if it's $e^{ln(\sqrt{q})}$
Then it's $e^{\frac{1}{2}ln(q)}$
Which is $\frac{1}{2}q$?
Ah, nvm
 
6:04 PM
When subtracting logarithms, there is a rule that
$log_{a}(\frac{x}{y}) = log_{a}(x)-log_{a}(y)$
What happens if there is a $2$ in there, like:
$log_{a}(x)-2log_{a}(y)$
Does it become $2*log_{a}(\frac{x}{y})$?
 
6:18 PM
Anyone?
 
@Owatch That is $\sqrt{q}$
@Owatch that is $\log_a(x)-\log_a\left(y^2\right) =\log_a\left({\large\frac{x}{y^2}}\right)$
 
@robjohn do you know about electronics?
 
@TheArtist A bit
 
6:33 PM
@robjohn any idea? ^^^^ :)
 
6:47 PM
@TheArtist An FET is a voltage controlled current source, where a non-FET is a current controlled current source.
 
@robjohn Thank You :)
 
it's actually more like a voltage controlled resistor, but under a constant voltage, that translates to a current source.
 
@robjohn I see :)
@robjohn were you a procrastinator at university while studying? How did you deal with it?
 
@TheArtist sometimes and sometimes not. I don't really remember how I dealt with it, because it sort of evened out.
I only remember cramming once, and it was with a group of others.
 
@robjohn Interesting, I see.....
 
6:56 PM
$e^{p} + 3 = \frac{1+q}{q}$
solving for q sucks.
Simplified all the way here, not sure what to try,
 
@robjohn last question that I dont know ^_^ ^^^ Please? ^_^
 
@TheArtist gate and source.
@TheArtist these are available on the web... why not look them up there?
 
@robjohn deadline in 5 mins :/ time is ticking
@robjohn Thanks alot :D your the best :D
 
@Owatch subtract $1$ and take the reciprocal.
@TheArtist Is this for a test? >8(
 
@robjohn homework I would call it :)
@robjohn what's >8( ? :)
 
7:02 PM
@TheArtist still... I looked them up on the web in that time, you could have, too. Then I would not have been an accomplice...
 
@robjohn I am sorry :/ I did google about FET and was looking at the wikipedia page, couldnt find the answers....so I asked you and I went to checking my other answers :/
 
@TheArtist The answer to the first question was in the first sentence or two and the second answer was at the beginning of the section on n-channel
 
@robjohn really? But when I read it I could not find it....
 
first sentence:
>The field-effect transistor (FET) is a transistor that uses an electric field to control the shape and hence the electrical conductivity of a channel of one type of charge carrier in a semiconductor material.
electric field = voltage
 
@robjohn oh I see.
 
7:11 PM
first sentence:
>In an n-channel depletion-mode device, a negative gate-to-source voltage causes a depletion region to expand in width and encroach on the channel from the sides, narrowing the channel.
 
@robjohn Oh I didnt catch that :/
it must have been because I was in a rush :(
@robjohn Thank you very much Rob :)
 
@TheArtist Learn about FETs for the test :-)
 
@robjohn I will for sure :) This was just a home work, and lately I have been delaying studies alot...
 
@TheArtist Without pen and paper $$\lim_{n\to \infty} \left(\frac{n}{\log(n)}\right)^2 \int _{\large 1/n^{1/n}}^1\int _{\large 1/n^{1/n}}^1\frac{1}{(x+y) (1+x y)} \ dx \ dy$$
There is a precise reason for which you look at it and know the answer.
 
@Chris'ssistheartist use latex :P without pen and paper ;)
 
7:25 PM
@TheArtist Anyway, it's too easy.
 
^^ was a joke :)
@Chris'ssistheartist Let me try :-)
@Chris'ssistheartist how are you btw :)
 
@TheArtist Very creative these days. You?
 
@Chris'ssistheartist Is the limit zero? :)
@Chris'ssistheartist Very bad I would say....neglecting studies
 
@TheArtist No
Well, that version is enough.
@TheArtist Later in life I finalized a university after dropping more, I know what you mean. I often found many of the studies a huge loss of time, and I was right. I was asked to write things on papers like 3-4 hours ceaselessly.
It was not for me this kind of stuff, and I felt often that the whole education system was such a big sh*t, nothing clever that kept me up.
Hours at uni should be like watching your favourite movies, maybe Star Trek? Well, yes, to make you return there, not just for the sake of finishing a school.
After hours one has to say "WOW, I'm looking forward the next hour!" As a professor, to come to hours and talk about your reseach, make kids curious about things you study, not just to talk about stuff known for hundreds years.
3
 
7:46 PM
Hello!
 
@Chris'ssistheartist How about $\Large{\infty}$ ? However I still think its 0....
 
@TheArtist No, no. Think of it some more. ;)
 
I'm doing a nice question that some of you might be interested in. brilliant.org/discussions/thread/…
A limit question
 
@Chris'ssistheartist Totally agree with your last point....btw so you didnt finish college? you dropped out?
 
@TheArtist I finished a uni after dropping others.
 
7:50 PM
@Chris'ssistheartist oh you went to several universities
 
@TheArtist Yeah.
 
@Chris'ssistheartist what was special about the last one
 
@TheArtist financial accounting - I felt attracted to it and I liked the way stuff was taught. Most of the time I was learning alone. I don't enjoy to stay in a room with many people, I don't feel comfortable.
I like very much to learn alone, without anyone around me.
:-)
 
@Chris'ssistheartist I see :) Miss Accountant
 
@TheArtist kind of ;)
 
8:02 PM
@Chris'ssistheartist ;)
@Chris'ssistheartist so you became an accountant and now a mathematician :) thats really good
 
@TheArtist Only If Euler and Ramanujan would admit that about me. I never think of the idea of being a mathematics, I simply do mathematics, and I do my best to do it like the giants previously mentioned. ;)
It's about the attitude towards mathematics, about the way to go, not about the final destination "I'm a mathematician now".
I like the way to go, and I enjoy so much to gather results, not for the sake of gathering results but often they show you how incredibly amazing mathematics is, an immense beauty that tends to $\infty$ (not that this makes much sense, but it is what I feel, huge amounts of pleasure that overwhelms you again and again)
 
@Chris'ssistheartist :) :)
 
What's the point to do mathematics and be bored? I would quit in that right moment.
 
@Chris'ssistheartist exactly...
 
I don't see anything so amazing like mathematics ... (that's true). It's bad many people will miss the huge pleasure given by mathematics for some reasons.
 
8:12 PM
How to solve $x^2 /leqslant 4$
 
@Chris'ssistheartist :)
 
@Ramanewbie A latex command starts with a \, not a /.
 
@Balarka Yeah tks, I haven't used Latex for a while...
How to solve $x^2 \le 4$ ?
 
@Chris'ssistheartist What is the answer to that limit ? :)
 
@TheArtist Don't you wanna think some more? :-)
 
8:18 PM
@Ramanewbie Rearrange to get $x^2 - 4 \leq 0$. Factorize to get $(x - 2)(x + 2) \leq 0$. Factor of two things negative $\implies$ one of the factors is positive and the other is negative. That gives you two cases : (i) $x \leq 2, x \geq - 2$ (ii) $x \leq -2, x \geq 2$. (ii) is of course impossible. Hence, $x \in [-2, 2]$.
 
How to solve this
 
@Chris'ssistheartist The reason why I think its 0 is because the $\lim_{n\to \infty} 1/{n^{\frac{1}{n}}}=1$ which makes the Integral limits from $1$ to $1$...
 
@BalarkaSen In fact I managed to get $(x - 2)(x + 2) \leq 0$
But then is there a formula to solve any $(x+n)(x+m)\le 0$ inequation, with n and m naturals ?
 
@Chris'ssistheartist maybe some hint?
 
@Ramanewbie You can answer your own question using a similar strategy.
 
8:21 PM
@TheArtist How does the integrand behave when the lower limits are very close to $1$?
 
@BalarkaSen "Factor of two things negative" What do you mean ? What are the 2 negative things ?
 
$(x - 2)(x + 2)$ is negative.
 
@Chris'ssistheartist Integral from $1$ to $1$ is zero....
@Chris'ssistheartist oh you meant integrand....
 
@TheArtist Yeah. But, well, don't miss the factor in front of the integral. :-)
 
If $ab$ is negative, then at most one of $a, b$ is negative, and the other is positive. This is an arithmetical fact.
 
8:24 PM
@BalarkaSen Ok I see what you mean.
 
Let $s_n$ be a sequence defined recursively by $s_0 = \sqrt{x^2 - x}$ and $s_{n+1} = \sqrt{(x^2 - x) + s_n}$ for $n \in \mathbb{N}$, for some $x \ge 1$. Let $L_x = \lim_{n \to \infty} (2x)^n (x - s_n)$. Then, prove or disprove,

$ \displaystyle \lim_{x \to \infty} L_x = \dfrac{1}{2}$
Any help with this?
 
@TheArtist When $n$ is large enough you have $$\frac{1}{(x+y) (1+x y)}\approx \frac{1}{4}$$
So, all reduces to the calculation of $$\frac{1}{4}\lim_{n\to \infty} \left(\frac{n}{\log(n)}\right)^2 \int _{\large 1/n^{1/n}}^1\int _{\large 1/n^{1/n}}^1 \ dx \ dy$$
@TheArtist this is just a disguised well well known limit, so it remains to uncover it. I let you the pleasure.
It's in front of you, just focus on it a bit.
Note that $$\frac{n}{\log(n)}= \frac{1}{\log(n^{1/n})},$$ and I don't say anything more. :-)
 
@Chris'ssistheartist Let me see :)
 
@MikeMiller Is the $H$-space structure $K(G, n)$ obtains from realizing it as $\Omega K(G, n +1)$ the same as the $H$-space structure coming from the group multiplication on $G$?
I am not sure if it is.
 
8:40 PM
ignore that
anyway, sure it is.
i can't provide a proof off the top of my head but it's no doubt true
 
ok, I'm believing you.
 
you can prove it
 
will come up with a proof tomorrow and ping you with it.
it is, again, dead of a night here.
 
@robjohn Thanks much for the help!
My questions are sporadic as I'm trying to help my brother out, and I'm finding I don't know things I should.
 
@DanielFischer
A Theorem I am studying states the following: Suppose $a \in \mathcal{A} := $ unital Banach Algebra and $\sigma(A) \subset \Omega$ open, then $\exists \delta > 0$ such that $\| x - a \| < \delta \implies \sigma(x) \subset \Omega$. Could you interpret this result as the spectrum can't suddenly expand but it can possibly suddenly contract?
 
8:54 PM
@Moses You can't deduce that the spectrum can suddenly "contract" from that. That theorem only tells you the spectrum can't suddenly expand (or jump around).
 
@DanielFischer I said 'possibly' :/
 
Oh, right.
 
 
2 hours later…
11:08 PM
I have this chatroom all to myself
 
11:31 PM
@AntonioVargas don't do anything the rest of us wouldn't do... that leaves you a LOT of leeway ;-)
 
@robjohn While you were away I've instituted a toll here. You'll have to pay up if you wish to contribute.
 
@AntonioVargas Oh, well, I guess I won't contribute.
 
@robjohn discounts are available for the elderly
 
Let's see... what does this button marked "Eject" do?
 
My reign is ending!
 
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