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10:00
@Brody find range
@Brody from which show is that?
bigger image ;)
@saturatedexpo it's called "Community" I think. never saw it myself
Yeah, it's Community
@DHMO got?
This is hint given
@Brody ah llol the last line isnt even right, but the 4 at the end wouldnt change the point.
also this method sucks if they are constants involved
(unknown constants)
10:06
@saturatedexpo the third equation down looks wrong
Oh nevermind, you're working backwards?
@BalarkaSen still trying to cheat a little. The transition matrix between the standard basis to the spherical frame should (I think) have orthogonal columns since the latter is an orthogonal basis. This transition matrix is the Jacobian at a given point, so doesn't this prove the orthogonality of the columns?
@saturatedexpo You wrote the $n+1$ form in the second line and went from there?
@Brody i found the error
multiplied out wrong
$(n+2)(2n+1)=(2n^2+n+4n+2)$ and not what stands there
@saturatedexpo You want to show assuming the $n$-th case implies the $(n+1)$-th case is true
What did you conclude about the $(n+1)$-th case in your work?
10:11
i made of $4^{n+1}=4*4^n$ and inserted
thats the whole point or not?
then the RHS times 4 of the assumtion
and then try to show that 4*assumtion is less then the final term
but forget to check in this picture, its a mess anyways^^
Hey everyone, quick question on convention, when denoting subsets do you guys mainly use $\subset$ notation or $subseteq$ notation?
I use $\subseteq$
@Perturbative both is valid and \subset is just more seen
The problem is that $\subset$ usually means $\subseteq$ and very sometimes $\subsetneq$
if A is strictly lesser then B i for mine will use $\subset$
10:15
So in that sense I find it safer to use $\subseteq$
for (not necessarily proper) subset of, I use $\subseteq$
for most things
it really doesnt matter
like the whole 0 being positive thing
if you're nervous readers might misunderstand, you can briefly remark your notation to clarify $[A\subseteq B]\Longleftrightarrow [(A\subsetneq B)\lor (A=B)]$
@saturatedexpo Assume $\exists n>1,\; 4^n\cdot(n!)^2 < (2n)!\cdot (n+1)$
@Brody now i finally understand where the (n+1) in the nominator comes from -.-
@saturatedexpo What you do to one side, you do to the other!
10:22
he made $(n!)^2$ to $((n+1)!)^2$. therefore he had to multiply both nominator and denomintor by $(n+1)^2$
but since he already has one (n+1) for "free" of the LHS
...
no
What is the issue here ?
i dont understand
@saturatedexpo Thats where $(n+1)^3$ came from, but the $n+1$ itself came from earlier
We have $\dfrac{4^n}{n+1}<\dfrac{(2n)!}{(n!)^2}$
@Astyx i dont understand this solution from super dooper math.stackexchange.com/questions/2008867/…
We want to make it look like the $(n+1)$-th case
So we go ahead and transform the LHS
10:25
how so?
times 4
$\dfrac{4^n}{n+1}\cdot\dfrac{4(n+1)}{n+2}=\dfrac{4^{n+1}}{n+2}$
that's the LHS, now it looks like the $(n+1)$ form we need
Wow this looks overly complicated
but we multiplied it by $\dfrac{4(n+1)}{n+2}$, we have to replicate that on the RHS
Do you want to understand the proof or specifically what he wrote ?
@Brody for 4^{n+1} also the 4
@Astyx i want to understand the steps he did
10:27
fixed, thanks
And which ones don't you understand specifically ?
the first haha
but brody got it i think :D
@saturatedexpo We multiply both sides by $\dfrac{4(n+1)}{n+2}$. That's where those extra terms, including the $n+1$ factor, come from
and now we got to show
that the RHS is smaller then the RHS?
Yes, now we work with the RHS side to drive the proof
10:29
wow i just didn get it haha
finally
@Arrow I don't understand what you're trying to do. I mean, just computing the Jacobian shows they have orthogonal columns and you can do it on your head.
@saturatedexpo See that $${{4^{n+1}}\over n+2} = {4^n\over n+1}{4(n+1)\over n+2}$$
yes we already worked that out :D
on the long way i guess xd
Then use induction hypothesis
There's no need to compute the basechange matrix from the standard base to the spherical one.
That's the harder way around.
10:34
ok now, why does he use: "so $\frac{4(n+1)^3}{(n+2)(2n+1)(2n+2)} <1$" why now the 1?
$$\dfrac{4^{n+1}}{n+2}<\dfrac{(2n)!}{(n!)^2}\cdot\dfrac{4(n+1)}{n+2}=\dfrac{(2n+‌​2)!}{((n+1)!)^2}\cdot\underbrace{\dfrac{4(n+1)^3}{(n+2)(2n+1)(2n+2)}}_{\text{less than } 1}<\dfrac{(2n+2)!}{((n+1)!)^2}$$
The quotient is less than 1. You can check that the difference in the polynomials is positive for $n>1$ @saturatedexpo
You could also see that $(2n+2) = 2(n+1)$ thus $${4(n+1)^3 \over (n+2)(2n+1)(2n+2)} = {2(n+1)^2 \over (n+2)(2n+1)}$$
^ better
wow i mean its cool, but not that intuitive for me
@saturatedexpo There's a method to it
10:38
And expanding the numerator and denominator, you get $${2(n+1)^2\over(n+2)(2n+1)} = {n^2+2n+1\over n^2 + {3\over2}n + 1} \ge 1$$
but 3/2<2 and therefore the fraction is >1?
wait
how does there a fraction get anyways
@Astyx huh?
>.>
Wait ..
$2n^2+n+4n+3$ is the denominator
the middle term has coefficient $\frac{5}{2}$ in the denominator
10:42
Oh yeah that's it
But I can't edit any more ...
yeah np ;)
ok
${2(n+1)^2\over(n+2)(2n+1)} = {n^2+2n+1\over n^2 + {5\over2}n + 1} \le 1$
but why we now take the fact that this is <1?
I think it's strict for $n>1$
ah ok
so for n=1 we have to show it by hand (which is trivial)
10:43
Move the denominator over, and take the difference of like terms
I personally feel dealing with this problems with fractions is a lot of hard work for little benefit. It's much more natural to show that $4^n (n!)^2 \lt (2n)!(n+1)$
yes
i tried, but no fruits
Factorials and fractions go well together though
Though I'm sure the other way might be the same, if not easier
It would probably be the same
@Astyx thanks for the edit
10:46
@Astyx Good editing over there
lol^
@Brody Isn't it midnight in your side of the world?
@BalarkaSen oh it's way past midnight...
Haha I personnally couldn't read a thing, that's why I edited :)
I guessed.
I'm on Eastern time. Same as New York City and Washington, DC
10:47
Ah.
Coming up on 6 am
yikes lol get some sleep
What's the time over there if I might ask?
but we have to strictly prove for n=0 and n=1 for a complete prove or?
about 4 PM
10:48
@saturatedexpo No. We must prove the inequality for $n>1$
So we consider $n=2,3,4,\ldots $
(hopefully not extending to non-integral $n$ lol)
i mean we must show the whole thing for those 2 cases
because the prove only shows for n>1
@saturatedexpo $\mathbb{N}_0=\{0,1,2,\ldots \}$?
yes
my bad!
10:50
then yes, those must be considered with the non-strict inequality $\le$ as posted
did not include that in the question ;)
but you can just show the $n=0$ case true and use induction to do the rest
so at <1 we might as well post $\leq 1$
yep, think so
mmh better not
because the whole thing builds on that being strictly less then one
10:53
@Brody I'm going to give you some homework for the next time we talk : learn and understand cross product and it's geometric meaning from chapter 1, section 5. Then we can talk about volume of surfaces and it's relation with Riemannian metrics.
@saturatedexpo doesn't matter, the proof itself needs a non-strict inequality now, so we can use that
$$\dfrac{4^{n+1}}{n+2}\le \dfrac{(2n)!}{(n!)^2}\cdot\dfrac{4(n+1)}{n+2}=\dfrac{(2n+‌​2)!}{((n+1)!)^2}\cdot‌​\underbrace{\dfrac{4(n+1)^3}{(n+2)(2n+1)(2n+2)}}_{\le 1}\le \dfrac{(2n+2)!}{((n+1)!)^2}$$
Nothing really changes, we proved what we needed to
@BalarkaSen Will do. Might take a couple days though
Sure, time isn't a factor. Also, chapter 3 section 5 contains a proof of equivalence of the two definitions of arclength. I think you'd be able to understand it just fine.
Feel free to not bother with any of these if you don't care though! I am just giving you "homeworks" to get you started and put something in the back of the mind as a motivation.
I feel like my brain continually atrophies without proper stimulation, so that's all welcomed. I'm also very endeared by your care and effort to spur another's growth in math
@saturatedexpo Some very nice proofs here
@Brody Yes, mine does that too. I think multivariable calculus, with appropriate care, can be very interesting 'cause it's the gateway drug to lots and lots of interesting mathematics. Ted does that a lot throughout the book, but since you already know some of the multivariable calc (although in a not very motivated way, as I gather), I think I can tell you a bit more.
And sure, I like to talk math with people who like math.
11:11
how do you use \underbrace{ properly? i want to have something under the brace (a small explanation)
$\underbrace{some text}_{text}$
oops
@BalarkaSen Multiple variables definitely make for more complicated math, but one can't ignore them.
meta.math.stackexchange.com/questions/5020/… answer titled additionnal decorations
@Brody Not complicated, beautiful! Differential topology/geometry, Morse theory, differential forms/de Rham stuff, more advanced analysis, etc.
i dont feel envy for my corrector haha
the fuck is so small cant even read it on pc
11:18
Ted also has a lecture on Fourier theory that I like a lot (it's not in his book).
Ted seems to know a lot
@Astyx that goes to my favs ;)
@Brody Yep, he sure well does!
@BalarkaSen I also wish the higher hyper-operations were better understood, even though they're not quite useful
hard to imagine that Ted thinks of someone that way :s
and even harder to imagine that the "bigger Ted" thinks of someone the way Ted thinks of him :O
11:23
@saturatedexpo Are you referring to @BalarkaSen as Ted?
@Brody I am not quite the tetration enthusiast here :)
@saturated Huh?
mmh, i dont think Balarka speeks of himself in the third person^^
@BalarkaSen suppose I wish mathematics were more complete in general. We have solid theorems and understanding of various algebras, various variables and dimensions, various hyper-operations, altogether working
@Brody Gödel
@saturatedexpo Gödel what?
11:26
@Brody That it's not is why it's fun!
it is already pretty big, to the point where we got statements that are true but cant be proven. So what is exactly your wish? That all subfields of Math work together?
i mean that taking a course in set theory makes you pretty much ready for everything?
@BalarkaSen Actually, there's some leisure in looking at the established repertoire and marveling at the objects and relationships we already understand. But that's just one aspect of the job
That's true. Well put.
There's also lots of adventure in exploring new territory, but that takes time and effort (which sometimes does not feel so leisure-full)
@Brody Could one explore if he doesnt feel happy about it? :s
meh im done
i take a pause :) till later and thanks @Astyx and @Brody ;)
11:32
My pleasure !
@saturatedexpo Think of sailing a ship to the New World. You have the shoreline in mind, but miles and miles of harsh sea life before you ever might reach it (like working an unsolved problem)
No problem :)
@Brody that analogy makes sense to me since Columbus had serious problems i guess with "point of no return" stuff
basicly suicide mission for glory? in math more like boredommission for knowledge^^
@saturatedexpo I'm sure some mathematicians work in part for the glory too
@Brody at least russians don't (well for glory maybe, but not for money)
is there a good lecture about ordered fields?
I think most people don't do math for fame or money.
11:37
Hello
@Qwerp-Derp welcome aboard :)
Uhhh can I request a formula for a thing?
I don't have any idea where to start
Don't ask to ask, just ask :)
well, post your problem :)
@BalarkaSen Albeit, corporate and government mathematicians generally get paid pretty well here
But that's a different 'mathematician' arguably
11:39
Uhhh
So n people are in a ring
(This is not the Josephus problem)
So 4 people for example, 1 2 3 4
I used the sneak-word "most", not "all" :)
The 2nd person is removed
so it becomes 1 3 4
the person after 2 is 3
And then because 2 is removed, we move forward 2 for the next person to remove
So the next person removed is 1 (3 -> 4 -> 1, moved forward 2)
And so on and so forth
isnt this equivalent to joesphus (i mean np, just saying)
11:41
Until one person is left, in this case 3
@BalarkaSen I often think about those career prospects for the income. It's a trade-off between academic pursuit and fiscal comfort
@saturatedexpo Is it?
just a different ruleset
True
It's really similar to Josephus
So if I understand correctly, if you have 10 people, you would remove 2,5,1,4,... ?
11:42
@Astyx Correct
I don't seem to find any patterns with the thing either
is the next person to be removed always the "p" person where p=last person removed?
@Brody Sure, I am not saying that choice is "wrong" or anything.
@saturatedexpo Yup, instead of Josephus's p=1
It's perfectly fine if one wants to secure their financial position.
try find a pattern, and look for shinies i guess?
try some circs maybe 1 to 5?
11:44
@Qwerp-Derp And if you have three persons, you would remove 2 then 3 right ?
also what is $p_0$?
@saturatedexpo I used matplotlib the formula for 1 - 10,000 I think
@saturatedexpo Only positives
@BalarkaSen I know. But I personally do seriously consider certain paths just for the money, even if to the potential diminution of learning rich, beautiful math
oh, so p_0 is unknown and n too?
@Astyx Yup
@saturatedexpo wait what n?
11:45
n=number of people at start
@Brody And also just for the fame
mmh, such a formular would be a generalization of josephus or not?
I don't think so
11:47
I think it's probably too random
@Brody Well, it's your decision after all. But be sure to always do what makes you happy!
The rule depends on the eliminated person thus the induction formula would be more complicated
Would a question asking for a formula on Math.SE be downvoted?
Not if you show your progress
(well one can never tell)
one upvote from me at least :P
11:48
@BalarkaSen Problem is feeling torn between the two. I'm probably not the only prospective who's dealt with this though
I honestly dont have much progress
I just have a plot and that's about it
(And a Python script)
is p_0 random or do you want a formular that calculates the person surviving f(p,n)=??
I kinda want a formula that calculates the person surviving (f(p))
yeah but that depends on the number of people too
I don't think there's any use for n, because we know that the person eliminated is always 2 at the start, and then it goes on from there
11:51
if p_0=1000, and the number of people $2^{100}$, what does it say?
Wait so we're starting with the 1001st person getting eliminated?
but we can't wait, because we have to (in josephus shoes) say at the beginning who has to start or not?
@Brody I don't have any useful suggestions for you because I haven't faced this situation (yet), unfortunately.
so the function has to (at first, we can probably express p_0 in n terms or other way around) be dependant of 2 variables, p_0 and n
11:56
@BalarkaSen That's alright. And perhaps better you never have money muddle your art
p_0 is where the "removing" process actually starts, right?
Isn't this a specific case of the Josephus problem?
I don't think so
The initial point is equal to the number skipped
@Qwerp-Derp yes, if p_0=5, then the 5th person gets removed, or 4 further then josephus
at least how i understand it
well
makes not much sense because if p_0=1 joesephus gets killed always
so one might say p_0 means the p+1th person gets killed
12:07
@Qwerp-Derp Could you give the winning positions for the first 20 tries please ?
12:21
@Brody money is an illusion. but math is forever there. matter of taste probably?
12:53
@TedShifrin Thanks, that makes sense.
 
1 hour later…
13:55
I need example of a probability space (Ω,β,p) such that Ω is an infinite sample space but |β| < ∞.
someone has any idea?
@TalShani $\Omega = \Bbb N$ and $\beta = \{\emptyset, \Bbb N\}$ ?
Basically $\beta = \{\emptyset, \Omega\}$ will always work
but then beta is infinite
No, $|\beta| = 2 here$
One of the elements of $\beta$ is infinite (since it's $\Bbb N$)
But this is unavoidable since $\Omega \in \beta$ by definition of $\beta$
and what do you think about this one?
example of a probability space (Ω, β, p) such that |β| = 3
is that possible?
I'd be tempted to say no
14:09
I'm trying to think what not
why*
Because $\beta$ must be stable under complementation (not sure about the english term)
one of the element is omega the second is the emptyset
Let $\beta = \{\emptyset, \Omega, A\}$
Then $\overline A \in \beta$
ok but what is
a
A
Your third element in $\beta$
14:11
but we said that is impossible
Yes I'm trying to prove it to you :)
haha thanks
Imagine it is possible, then $\beta = \{\emptyset, \Omega, A\}$
Thus $\overline A \in \beta$
However $\overline A \ne A$ (otherwise $\Omega = \emptyset$ and that mean $|\beta| = 1$)
14:14
i think i know how to prove that
the same like you said
If $\overline A = \emptyset$ then $A = \Omega$ thus $|\beta| = 2$
If $\overline A = \Omega$ then $A = \emptyset$ thus $|\beta| = 2$
bc A is closed under complements
Therefore $|\beta| \ne 3$
Yup
and this one:
an example of a probability space (Ω,β,p) such that |β| is an odd integer or prove that no such a probability space can exist.
i think it must be even right?
Yes
Do you know about equivalence relations ?
It would be suited in this case
14:16
not really
Mm then it's tricky
The idea is to say that you can group the elements of $\beta$ by pair consisting of an element and its complement
Can $\Omega$ be $\emptyset$ ? (I can't remember)
i dont think so
so beta has to be even?
Well then you can do what I'm telling you, group the elements of (the formal term is "partition") $\beta$ by pairs
And see that $|\beta| \in 2\Bbb N$
exactly
but how can i prove that?
in formal way?
Well what I would do is introduce the binary relation $\sim$ such that $$\forall A,B \in \beta, A\sim B \iff B \in \{A, \overline A\}$$
See that it is an equivalence relation
14:23
ok
Parition $\beta$ with it.
thank you so much!!
And see that any equivalence set has cardinal 2
It's my pleasure !
14:47
Would one of you have any lectures concerning binomial coefficient (in)equalities and efficient approaches towards them ?
Hi
what's the inequality you're aiming for again?
Not one particular
I'm just looking for tricks
ah.
can't say I have a good source in general
14:50
Thanks any way :)
15:34
It's been a while, and I don't remember. Do badges on this site award additional Reputation Points?
I do recall that badges take forever and a day to be rewarded, due to the automated process that is used
16:16
So this question of mine from last year finally got answered:
4
Q: Writing $\sqrt[\large3]2+\sqrt[\large3]4$ with nested roots

Akiva WeinbergerLet $C\subset\Bbb R$ be the smallest set containing $0$ and closed under whole number addition/subtraction, whole number exponents, and whole number roots. That is, for all $c\in C$ and $n\in\Bbb N$, we have $c\pm n\in C$, $c^n\in C$, and $c^{1/n}\in C$. We know that $\sqrt2+\sqrt3\in C$, since ...

you should celebrate and throw a party
your question reminds me of another one
that only accepted, I think, square root and adding an integer
and it had a half-dozen non-trivial examples of things
@mercio Care to share a link?
sadly I don't think it's in my favorites
after giving them a glance
42
Q: Converting sums of square-roots to nested square-roots

SomniumWhen solving different equations, I have realised, that some roots containing only arithmetic operations and square roots (4th, 8th roots too, because they can be represented using only square roots) can be converted to nested square roots form. Examples (these are roots of equations of 2nd, 4th,...

(i didn't glance hard enough)
16:35
Would it be acceptable for me to accept an answer on this question I posted a while ago?
3
Q: Summing of factorials to produce perfect cubes

teadawg1337I was playing around with factorials the other day, and I realized that $4!+5!$ is a perfect square. Perplexed by this result, I started looking for other pairs of factorials that produce a perfect square when added together (unbeknownst to me, I had stumbled across a well-known open problem in n...

Or has it been too long?
feel free to accept an answer iff you feel it deserves it
The answer I want to accept doesn't fully answer the question, but I think it's the closest I'm gonna get
lol its true
this site is self moderated what is or is not acceptable is in a state of flux with active users
@TobiasKildetoft mathoverflow.net/questions/254453/… This was a good question imo.
i doubt anyone would want to do anything unless you choose a really wrong answer and even then probably people wont care but it brings the question back to the active list
16:52
Can someone give me a hint for iii)?
I am not sure how those two functions will help me find all the congruency classes
17:19
When would it be reasonable to start a bounty on an unanswered question? I asked this question a week and a half ago, and it still has no answer. I've been stuck on the problem for months, but I'm thinking I should wait another month or two to start a bounty
8
Q: Closed form for $\int_0^e\mathrm{Li}_2(\ln{x})\,dx$?

teadawg1337Inspired by this question and this answer, I decided to investigate the family of integrals $$I(k)=\int_0^e\mathrm{Li}_k(\ln{x})\,dx,\tag{1}$$ where $\mathrm{Li}_k(z)$ represents the polylogarithm of order $k$ and argument $z$. $I(1)$ evaluates to $e\gamma$, but $I(2)$ has resisted my efforts (wh...

Although, a bounty probably won't really do much anyway
17:49
The more I look at it, the more I question whether a better form is even possible
what does double dollar mean in latex?
bigger equations?
i mean dd some text dd
It displays the contained text on its own line
It also makes some symbols bigger and easier to read
thats good :)

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