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01:05
What is the type of continuation called when you continue a function defined on the naturals to one on the reals?
the-continuation-which-made-the-gamma-function
It's not an analytic continuation.
> In mathematics, the gamma function (represented by the capital Greek letter Γ) is an extension of the factorial function
They just call it an extension, lol.
Yeah, but extensions by themselves are not unique.
I could easily extend the factorial function by splicing a random-function in-between all the naturals
Generalization
natural-to-real continuation
coin your own terminology.com
01:08
I'm looking for a term that people actually use so that I can find content discussing it.
What's your function?
I want the same power as an analytic continuation, which boasts the uniqueness of the result of the continuation.
The Harmonic Numbers sequence.
$H_k = \sum_{n = 1}^k \frac 1 n$
And what is the continuation?
That's just it. I know there exists a continuation that everyone uses all the time, based on the gamma and polygamma functions.
But I can't find out how they found it.
It's something like $\gamma +\psi^{(0)}(1+k)$
Then how is it not an analytic continuation?
01:11
An analytic continuation requires an analytic function to begin with.
A function only defined on the naturals is not complex differentiable at any point in its domain.
Not only that, I'm fairly certain that the naturals form a closed subset of the complex plane, since their complement is clearly open.
I don't have much to work with here, at least given my existing knowledge on the matter.
Not sure if this helps: $H_n\approx\ln(n)+\gamma+\dfrac1{2n}-\dfrac1{12n^2}$
While that's a very useful approximation, I'm not sure if it helps either.
Which means it doesn't help :(
you could just use this to the reals, lol
01:14
While I could use the approximation, the approximation is not the continuation I'm looking for.
By the sheer nature of being an approximation, it's no longer an extension.
I am not sure if the partial sum has an exact representation
@LeakyNun I've read through a bit of the page on Wikipedia for the Gamma function, they claim its an analytic continuation, but I can't believe it just yet.
(Ignore me) $\int_n^{n+1}f(x)\ \mathrm dx=\frac1n$
A function on the naturals is not infinitely differentiable in the space of reals or complex numbers, is it?
*$\int_n^{n+1}f(x)\ \mathrm dx=\frac1{n+1},\ n\in\mathbb N$
01:24
@LeakyNun What are you using as $f(x)$?
Hey, @TedShifrin
I am trying to find such function
Hi @Axoren and @Leaky
@TedShifrin Good morning.
It's really (meromorphic or) analytic continuation once you have a functional equation that needs to be satisfied.
@TedShifrin Maybe you could answer this swiftly and put an end to my confusion. Are functions only defined on the natural numbers analytic?
01:25
@Axoren Of course not.
That makes no sense, really. You need an open domain to talk about analyticity.
Analytic continuation makes the function analytic.
Then how is $\Gamma(x)$ an analytic continuation of $(n - 1)!$?
But analytic continuation is normally done from one (open) domain to a larger domain.
Because $(n-1)!$ isn't analytic and $\Gamma(x)$ is!
01:26
That's what I thought.
Now wait, hold on. I thought you could only analytically continue analytic functions.
First of all, the gamma function is only meromorphic. I would not use the word "analytic continuation" therewith.
That's just Wikipedia playing a dangerous game, then: en.wikipedia.org/wiki/Gamma_function
That's not the right setting for analytic continuation. You can say it's a meromorphic function extending the factorial function on the positive integers.
No, wiki is moderately careful. They say that the gamma function is an extension of factorial and then that function makes sense on $\Bbb C$ if we allow poles.
Oh, I see.
(Ignore me) $F(n+1)-F(n)=\frac1{n+1}$
01:30
But they do abuse the language, in my opinion. They talk about analytically continuing the gamma function defined just on the positive real axis. That is wrong.
@TedShifrin No, that is not what the wiki says
> by analytic continuation to all complex numbers except the non-positive integers
Well, if I was able to solve that equation, I would be world-famous
so I just give up
Oh, you're right. They are correct. They say the integral formula for the gamma function is analytic on all of the right half-plane in $\Bbb C$, and then they analytically continue. Perfect.
Hello, guys. I just have a simple question and Googling it didn't help too much. Are the multiplicities of the eigenvalues of a matrix in the minimal polynomial equals to the dimension of the corresponding eigenspace?? It seems I've already seen this result before, but I can't find it anywhere! Do you have some links, or whatever...
@Leaky: Those are the harmonic numbers. I dunno what you mean about "solve."
@TedShifrin Functional equation: $F(n+1)-F(n)=\frac1{n+1}$
01:33
That's some muddy language, in my opinion. I misunderstood it the first time reading it.
If I made a mistake, it's the source's fault, not mine.
@Anderson: Not really.
For example, for the identity, the minimal polynomial is $p(x)=x-1$, but the eigenvalue has multiplicity $n$.
Even for the generalized eigenspaces?
I really think I've already seen something like that...
If the minimal polynomial is $p(x)=(x-1)^k$, that tells you that the dimension of the largest generalized eigenspace is $k$.
But we have to be careful here.
That excludes regular eigenspaces :P
What is the current record for the time-complexity of bitwise squaring, in terms of number of bits $n$?
Hi guys. Does this question have a positive answer? math.stackexchange.com/questions/1572743/…
01:36
@LeakyNun I think it's $n \log n$ because you can alternate adding and shifting based on which bits are 1 and which are 0.
@Axoren Multiplication is $n\log(n)$, I thought squaring could be better
Wait, hold on.
Thank you guys!
I don't know if the information that the number is the same contributes to a more efficient multiplication.
It probably does, now that you mention it
But I don't see how immediately.
@Bananach: I don't understand. In the original statement, what norm is being used in the first place?
01:39
@Axoren $(2n+1)^2=4n^2\mbox{ (constant time) }+\mbox{ (O(n) time) }(4n\mbox{ (constant time) }+1\mbox{ (constant time) })$
@LeakyNun Are you working with truncated results? where the result only needs $n$-bits?
@TedShifrin the norm infinity as well
@Axoren The result needs $2n-1$ bits
When I said "I don't see how", I meant the means by which it attains the lower time-complexity is what eludes me.
@Bananach: Isn't the question answered in the original thread? It looks like it to me.
01:42
@TedShifrin I thought maybe they were referring to some counterexample which can be constructed by way of convolutions
@LeakyNun That's a shame on the result's size. Were you working in a computer, you could cut the multiplication short because all the carries fall off into oblivion.
@Axoren Never mind, my algorithm is still $O(n^2)$ I believe
@Axoren Python. Or BigInteger, for that matter.
No, go back to the original post.
Oh, good, MSE is down.
@TedShifrin Not for me.
Well, dinner time for me. :)
01:44
@TedShifrin Peace, thanks for the help earlier.
Sure thing.
@LeakyNun There was this method for bitwise field arithmetic that worked rather efficiently. I'm trying to remember what it was.
@Axoren Fast Fourier transform?
Nope, simpler.
nice, because I don't even understand FFT
01:46
Essentially, you would iterate over the bits of a number. If it was a 1, you add the original number to the result buffer. If it was a 0, you double the result buffer.
FFT is cool. Luckily, it's not needed here. Cool things are scary to use.
The benefit of the mechanisms you have there is that multiplication by 2 is essentially a bit-shift left.
@Axoren If it is a 1, you add the original number to the result buffer after doubling the result buffer
I just wrote a recursive online algorithm based on $(2n+1)^2=4n^2+4n+1$
Right, I missed that part.
but it was $O(n^2)$ time I believe
That may have been because of improper tail-recursion.
What do you mean?
01:48
Python's interpreter will optimize your recursive functions if they're in tail-recursive form.
If the recursive call is the last statement in the function, you don't accrue additional variable assignments of function stack space.
So calculating your time and space complexity empirically will show higher time spent and higher memory spent.
So what should be the time complexity?
Oh, and by "I just wrote", I really mean "I just thought of"
Depends on how you made your recursive function.
@Axoren What's your native (programming) language?
Java for 10 years, Python for no where near as main.
C somewhere in there, back in 2009.
C++ is a mess. Touched it once, sent it to the pits never to return.
Then I'll write it in Java then
01:52
Why?
because Java is your main language
That's a terribly idea.
Why would you write a function in someone else's native programming language?
Because I speak both Java and Python
and Java is my main language
01:53
That's a better reason.
Java's compiler does have tail-recursive optimizations as well.
However, Java requires a lot more boilerplate before getting a single function to operate in it.
I like it because I like boilerplate, but I recognize that it's terrible for just getting down-and-dirty with a single function.
public long square(int i){
	if(i==0 || i==1) return i;
	if((i&1) == 0) return square(i>>>1)<<2;
	long temp = square(i>>>1);
	return (temp<<2) + ((i<<2) | 1);
}
definitely not tail-recursive, right
Of course.
The recursive call is in the middle of the function, rather than the tail-end of it.
I don't quite care, I just count the number of iterations
in this case it is $n$
Personally, I'd write recursive code in Haskell if I get to choose.
Let's get back to the main topic
This code is $O(n^2)$ right
01:57
Let's ignore the degenerate cases of 0, 1, etc.
Your main work-horse if-statement has two cases.
I could write it in closed-form
The first case performs $square(x/2)*4$
but it would be a pain in the butt
The second case performs $square(x/2)*4 + c$
$+4x+1$
01:59
Yeah, that thing.
That's $c$
and then?
What's the cost of multiplying by 4?
O(n), right?
But every time you do it, you do it on linearly fewer $n$.
So it's as if at each iteration, you did it on $n/2$
@Axoren O(0.5 n^2) is still O(n^2)
This becomes $n^2$
@Axoren Why not O(1)?
02:02
What's the sum of $n$ from $n_0$ to $1$?
@Axoren 0.5(n0)(n0+1), which is still n^2
Right.
Maybe I misinterpreted you, given that you were so quick to identify that relationship.
What did you mean by $O(1)$?
Which part?
I could use little-endian to make multiplying by 4 constant time
@Axoren multiplying by 4
Hmm.
If that's the case, then you're left with $O(n)$ just considering the $square(x/2)*4$
But that's too amazing.
no, I analyzed it completely before
02:05
You now have to consider case two in your workhorse if-statement.
26 mins ago, by Leaky Nun
@Axoren $(2n+1)^2=4n^2\mbox{ (constant time) }+\mbox{ (O(n) time) }(4n\mbox{ (constant time) }+1\mbox{ (constant time) })$
The $O(n)$ time is $+$
Right, from case 2.
The only place where you do it.
yep.
So the best case is $O(n)$ and the worst case is $O(n^2)$
Yup.
You have to calculate that out.
What does it mean for the average time complexity to be $O(f(n))$?
In a nice problem like yours, we can consider good-enough estimates of the average-time complexity.
In particular, if $m$ is the number of $1$s in the number, the complexity is $O(nm)$
02:09
You're already ahead of me on that.
So, now consider $E_m(O(nm))$
So we fix the number of digits?
$\sum_{m = 0}^n m O(nm)$
$\displaystyle2^{-n}\sum_{m=0}^n\binom nmO(nm)$
I'm fairly certain we can just do it this way.
By the average number of flipped bits.
Rather than by the average of all possible bit-strings
Yours is more precise.
$\sum\binom nr=2^n$
Oh!
$r\dbinom nr=r\dfrac{n!}{r!(n-r)!}=n\dfrac{(n-1)!}{(r-1)!(n-r)!}=n\dbinom{n-1}{r-1}$
$\displaystyle2^{-n}\sum_{m=0}^n\binom nmO(nm)=2^{-n}\sum_{m=0}^{n-1}\binom {n-1}mO(n^2)=0.5O(n^2)=O(n^2)$
@Axoren right?
02:24
I'm fairly certain you're on the money.
@Axoren What does "on the money" mean?
Correct.
$\displaystyle\sum_{r\mbox{ odd}}^{2n}\binom{2n}r = \sum_{r\mbox{ even}}^{2n}\binom{2n}r$
Thanks
Prove it by induction, lol
(just horsing around)
02:26
I prefer proof by definition, myself.
It is because I say it is.
nice.
So, I found out more about the harmonic numbers.
Apparently, there's a good way to define them with a continuous function.
care to share?
$\frac{1 - x^n}{1 - x} = 1 + x + x^2 \dots x^{n-1}$
$\displaystyle\sum\frac1k=\sum\int_0^1(x^{k-1}\ \mathrm dx)=\int_0^1\frac{x^n-1}{x-1}\ \mathrm dx$
02:29
Yup.
I just thought of that, lol
It's disgusting yet elegant.
An abhorrent mess of beauty.
That function extends the Harmonic Number to the reals.
nice.
02:45
Is anyone interested in this?
Find $\displaystyle\sum_{n\mathop=0}^\infty\frac1{\tbinom{3n}{n}}$
@LeakyNun Mathematica returns that as a hypergeometric-3F2 function, and doesn't simplify further
@Semiclassical Could you test Mathematica on $3n$ replaced with $2n$?
heh, you read my mind
it comes back with $\frac{2}{27}(18+\pi \sqrt{3})=1.7364$
Good.
Could you test $4n$?
in that case it comes back with a hypergeometric-4F3
so it seems to follow that pattern of $kn$ giving a hypergeometric-kF(k-1)
02:55
and I have no idea what a hypergeometric is.
there might be a simplification, but mathematica doesn't know it.
ehh. it's just a fairly generic power series sum
and what is the power series?
I mean, what is the series that it returns?
it's in there. that's pretty much the definition.
so when mathematica returns that, it's basically just a rewriting. doesn't really give anything deep.
02:57
It's impossible that Mathematica just doesn't know it.
Mathematica knows everything.
hahahahahaha
yeah no
$\displaystyle\binom{3n+3}{n+1}=\frac{(3n+3)!}{(n+1)!(2n+2)!}=\frac{(3n)!(3n+1)(‌​3n+2)(3n+3)}{n!(2n)!(n+1)(2n+1)(2n+2)}=\frac{3(3n)!(3n+1)(3n+2)}{2n!(2n)!(n+1)(2n‌​+1)}$
@Semiclassical Could you help me ask mathematica this?
1.41432204432182039186500394383124895084527274214395277647
03:18
that does seem to match what mathematica gives for your earlier series, yes
Is there any deeper significance to the fact that $|z|$ and $\operatorname{Re}(z)$ — at least, modifications of them — are the elementary symetric polynomials of $z$ and $\bar z$?
$|z|^2$ and $2\operatorname{Re}(z)$
@Semiclassical It still returns the geometric whatever?
Fascinating.
I guess it means that anything symetric with $z$ and $\bar z$ can be rewritten in terms of $|z|$ and ${\rm Re}(z)$. Like, $z^2+\bar z^2=4\operatorname{Re}(z)^2-2|z|^2$.
03:55
@MikeMiller I don't think that's correct. The definition I gave said $g(\gamma)$ and $\gamma$ do the same thing to the particular element $\overline{m}$, but didn't say anything about doing the same thing to the whole fiber. Indeed if I understand correctly, principal $G$-bundles over $\Bbb S^1$ give counterexamples to [$g(\gamma)$ not depending on choice of lift $\overline{m}$] and to [$g(\gamma)$ acting the same as $\gamma$].
I collected all my thoughts into a question.
04:32
Obviously you're right, changing the lift of basepoint conjugates the homomorphism by whatever g you changed the lift by.
Fix your lifted basepoint x, pick loops $\gamma$ and $\eta$ downstairs, abuse notation and call their lifts by the same letter. Say $\gamma(1)=gx$, $\eta(1)=hx$. Concatenate $\gamma$ and $g\eta$ upstairs to get the lift of $\gamma * \eta$ downstairs.
Then upstairs you end at $g\eta(1) = gh$ as desired.
My nonsense claim from before would imply that by changing the basepoint upstairs to $gx$, $g\eta$ would end at $hg$, which is silly as you note, arctictern.
@arctictern Meant to ping. If there's stuff in the question unanswered, let me know and I'll take a more careful look as my penance.
 
2 hours later…
06:49
Paper done. Now to read through it a final time, missing all sorts of obvious errors and typos because my brain knows what it was supposed to say :)
07:05
I've deleted a recent post, since a second deduced statement was obvious. The first one is

**Lemma.** If $M=2^p-1$ and $M=2^{p'}-1$ are two distinc **Mersenne primes,** thus we can take $p<p'$ then $$\sigma(M) \left( 1+\sigma \left( \frac{M'+1}{M+1} \right) \right) =2\sigma(M').$$
I don't know if this is interesting or was in the literature. Now if you take in your hands to think and take new taks about it, you are welcome.
@user243301 what is $\sigma$?
sum of divisors?
The zeta function associated with a symmetric matrix.
@MatsGranvik Pretty colours (I guess...?)
I've deleted a recent post. The statement that still could be interesting, is the following:

**Lemma.** Tt is possible to show for a **Markov triple** $(a,b,c)$, that $$rad \left( \frac{a^2+b^2+c^2}{3} \right)=rad \left( \frac{a^3+ab^2+ac^2}{3bc} \right)rad \left( \frac{b^3+ba^2+bc^2}{3ac} \right)rad \left( \frac{c^3+ca^2+ab^2}{3ab} \right),$$
where $rad(1)=1$ and for $n>1$, $rad(n)$ is defined as the product of distinct primes dividing $n$.

I don't know if this is interesting or was in the literature. Now if you take in your hands to think and take new taks about it, you are welcome.
07:13
@user243301 I am not sure I understand the point of posting these here. Also, what do you mean by taks?
@TobiasKildetoft yes the sum of divisor function, for example $\sigma(8)=1+2+4+8$
@user243301 so both sides are just suitable powers of $2$
@TobiasKildetoft since I am deleting posts (marked as favorites of people), but were poor in their contents, perhaps it is interesting to some people. In the other hands I say that perhpas some people want try do more experiements. I believe that my two previous staments, as I've said are poor, but perhaps in hands of other user, that can modify those or it is a start point to deduce new things. Thanks
Bye Tobias and Mats good morning.
Taks was a typo, I want to say tasks
07:52
I have a question about deleting posts :D I have asked a question recently and figured it was full of miscalculations. So I think it´s of no use to anybody anymore. Do you think I should delete it? Is it considerd a right thing to do on this forum?
@Cornelis You can't delete a post if it already has answer
@lea
@LeakyNun ok, that solves the issue :D Thanks anyhow
welcome
 
1 hour later…
user174558
09:24
@Cornelis You can always click delete and see what happens. There is no right or wrong thing, just do it. This is not a crime, lol.
"You have your way. I have my way. As for the right way, the correct way, and the only way, it does not exist." Friedrich Nietzsche
 
1 hour later…
10:36
Is it possible to analytically continue an eigenvalue?
@MatsGranvik an eigenvalue of what? Seen as a function from where to where?
@TobiasKildetoft An eigenvalue of a matrix.
@MatsGranvik That is just a number. It does not really make sense to continue it analytically
11:14
This is so strange: math.stackexchange.com/q/1832867/12384 Don't teachers use $\neq$ in school anymore? What is happening? Do they just use PowerPoint these days and type != ??
lol @Szabolcs nope
it seems like that guy is just someone that got so used to programming
that he forgot the neq altogether
12:14
Finally. Paper completed and submitted to arXiv
12:32
@TobiasKildetoft Congrats!
@AndrewThompson thanks
12:51
Now to figure out a suitable journal to submit it to.
13:49
If you want to be 100% sure about the outcome of submitting your paper, there's always the JofUR
@SteamyRoot Your name. It's not in my list. What root finding algorithm does SteamyRoot refer to?
None that I know of
It's just an anagram of my real name
Invent one that exploits some insight about the way steam condenses into droplets in a closed space or something...
But if I ever come up with such algorithm, I now have a name to give it
Hahahaha
14:42
hey mathers
14:53
@agawa I just realized you were talking to the chatroom as a whole. thought someone in here was named mathers :D
@Agawa001 bonjour.
hi
@Obliv lol
@LeakyNun salut
@Agawa001 ça va?
@LeakyNun pourquoi pas ?
et toi tu te portes bien ?
14:57
oui
tu viens là avec une question?
je suis regulier dans ce chat et je frequente cette place par coutume
d'accord
parfois je viens pour poser des questions, d'autres fois je reponds aux questions, mais maintenent j'ai rien a contribuer
d'accord
@anon nah, i am a dumb person. or are you saying you're temporarily being me as in being dumb?
;)
15:03
@LeakyNun tu etudies le français dans un programme scolaire ou volontairement ?
@Agawa001 les deux
mais j'ai arrete le programme ilya longtemps
guys is $(1~2~3) \circ (1~3~2) = (1~3)(2~3)$?
and is $(1~3~2)\circ(1~2~3) = (1~2)(1~3)$ if not, why not?
@Obliv What is $\circ$?
function composition for cycle notation
these are elements of $S_n$ the symmetry group
never mind
15:09
@MikeMiller "But nobody likes me ..." I object. I think you're quite popular among the topology crowd here, a great teacher as you are.
j'ai etudie le francais pour un moment il y a longtemps, bien que je ne sais pas comment on utilise ce langue coloquialmente parce que mes professeurs etaient enneyeuse. ...aussi, mes verbes sont probablement horrible apres 3 ou 4 ans
cette langue
ennuyés ou ennuyants*
):
I'm at least satisfied I can still get a point across modulo a couple tiny problems
Tu sais, les agrements, ils sont horribles
quant tu te sers d'un pluriel qui regroupe m / f , l'adjectif qui le qualifie ne vient jamais en féminin
@SamuelYusim vos professeurs sont de quel sexe ? masculin ou feminin ou metissés ?
15:27
@Agawa001 On etudie francais?
en France
@BalarkaSen Hey Balarka! I thought you died or something
@LeakyNun oui en effet
actuelment, elles etaient tous femmes. je ne realisais, etrangement
@Agawa001 On etudie quoi?
@LeakyNun ce qui te plait
15:29
@Agawa001 J'ai voulu dire, on etudie quoi au sujet de francais en France?
@SamuelYusim mmm oui bizzare ! d'abord a cet occurence tu devrais dire "ennuyeuses" ou "ennuyantes" (more strange thing is how french beauty could ever annoy you lol)
I was also alternatingly taught quebequois french and french french which is kind of weird
le quebecois est un accent non plus une langue !
@Agawa001 "quebequois french" is a valid term
hmm lemme check it out
15:36
just like British English and American English
@Agawa001 What does "plus" do here?
@Krijn not "at all"?
Ah, okay
My French is not parfait
oui, mais il y a les differences. par example, en francais quebequois, on n'utilise un espace avant la ponctuation
@SamuelYusim par exemple?
15:38
quebequois: "par exemple?", francais: "par exemple ?"
hein... interessant
je ne le sais jamais
je pense que l'espace est vraiment bizarre
@SamuelYusim trop futile!
not as much as the two english accents differ from
yeah, verbally they're definitely closer to each other
like "z" vs "s" prounonciation
15:40
@Agawa001 pronunciation*
for example?
in french it is spelled "prononciation"
in English it is spelled "pronunciation"
these two langs are overlapping in my head
in English, you also capitalize the language's name
Tandis qu'en francais, on ne capitaliser pas des noms des langues
@LeakyNun like booze and boose
15:47
@Agawa001 what is a booze and what is a boose?
its to be hungover
both has same meaning, but in different accents
I see, thanks
well there is much like this i hope someone more versed in english language can point out more differences here
@Agawa001 Well, color vs colour, capitalize vs capitalise
(AmE vs BrE)
oh yes
15:50
mais ils sont tous differences d'orthographe
but they are different
flavor and flavour counts ?
@Agawa001 same difference as color vs colour
ok thanks

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