Welcome,
Guest
. Please
login
or
register
.
Did you miss your
activation email
?
1 Hour
1 Day
1 Week
1 Month
Forever
Login with username, password and session length
Home
About
Team
Rules
Stats
Status
Sitemap
Chat
Downloads
Forum
News
Our Projects
Major Community Projects
Recent Posts
Unread Posts
Replies
Tools
SourceCoder3
Other Things...
Omnimaga Radio
TI-83 Plus ASM File Unsquisher
Z80 Conversion Tools
IES TI File Editor
Free RAM areas
Comprehensive Getkeyr table
URL Shortener
Online Axe Tilemap Editor
Help
Contact Us
Change Request
Report Issue/Bug
Team
Articles
Members
View the memberlist
Search For Members
Buddies
Login
Register
Omnimaga
»
Forum
»
General Discussion
»
Other Discussions
»
Math and Science
»
A Math Challenge: Proof that sum(sin(x),x,0,infinity)=(1/2)*cotan(1/2)
« previous
next »
Print
Pages: [
1
]
Go Down
Author
Topic: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=(1/2)*cotan(1/2) (Read 10588 times)
0 Members and 1 Guest are viewing this topic.
Nosferatu Arucard 1983
LV2
Member (Next: 40)
Posts: 28
Rating: +6/-0
A Math Challenge: Proof that sum(sin(x),x,0,infinity)=(1/2)*cotan(1/2)
«
on:
November 08, 2012, 10:00:18 pm »
Since the infinity sum of sin(x) from x=0 to infinity (sin(0) + sin(1)+ ...) don't converge, we can use the Abel-Plana formula to calculate a renormalized sum of the former divergent sum:
sum(f(t),t=0 to infinity) = f(0)/2 + integrate(f(t),t,0,infinity) - i * integrate((f(i*t) - f(-i*t))/(exp(2*pi*t)-1) , t, 0 ,infinity)
But today I only show the problem, waiting to someone to try solve this ridle.
Edit: A minor fix to the result.
«
Last Edit: November 09, 2012, 01:23:26 pm by Nosferatu Arucard 1983
»
Logged
aeTIos
Nonbinary computing specialist
LV12
Extreme Poster (Next: 5000)
Posts: 3915
Rating: +184/-32
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #1 on:
November 09, 2012, 04:00:31 am »
Welcome to omni
I won't be able to proof that though.
Logged
I'm not a nerd but I pretend:
Builderboy
Physics Guru
CoT Emeritus
LV13
Extreme Addict (Next: 9001)
Posts: 5673
Rating: +613/-9
Would you kindly?
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #2 on:
November 09, 2012, 05:53:44 am »
Welcome to Omnimaga indeed
And I am a little confused by your notation. When you say Sum, do you mean integral?
Logged
aeTIos
Nonbinary computing specialist
LV12
Extreme Poster (Next: 5000)
Posts: 3915
Rating: +184/-32
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #3 on:
November 09, 2012, 05:54:58 am »
no I think it means the iterative sum >sigma notation?
Logged
I'm not a nerd but I pretend:
Adriweb
Editor
LV10
31337 u53r (Next: 2000)
Posts: 1708
Rating: +229/-17
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #4 on:
November 09, 2012, 07:47:06 am »
I'm gonna think about that, it looks inteesting
And btw, you sir deserve 1 internet for making WolframAlpha crazy (first time I actually see something like that on it) :
Logged
My calculator programs
TI-Planet.org
co-admin.
TI-Nspire Lua programming
:
Tutorials
|
API Documentation
Nosferatu Arucard 1983
LV2
Member (Next: 40)
Posts: 28
Rating: +6/-0
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=-(1/2)*cotan(1/2)
«
Reply #5 on:
November 09, 2012, 07:56:40 am »
When I mean sum is the usual sigma notation.
I will show gradually the proof of this renormalized sum, so be aware.
I'm also the main author of a portuguese written book of Special Functions that I publish in Amazon: "Introdução à Função Zeta e Gama de Riemann": Introduction to Riemann Zeta and Gama Function.
The proof of Abel-Plana formula was derived in Theorem 7.3 of my book
But I will translated to you...
1st Step:
Just apply f(t)=sin(t) to the Abel-Plana Equation, and it give:
sum of sin(t) from t=0 to infinity = sin(0)/2 + integral(sin(x),x,0,infinity) + i * integral(2*sinh(t)/(exp(2*pi*t)-1),t,0,infinity)
sum of sin(t) from t=0 to infinity = integral(sin(x),x,0,infinity) - integral(2*sinh(t)/(exp(2*pi*t)-1),t,0,infinity)
Since sin(i*t) = i* sinh(t) and sin(-i*t) = - i * sinh(t).
If you ask it, I can publish the proof of Abel-Plana by steps.
«
Last Edit: November 09, 2012, 08:22:06 am by Nosferatu Arucard 1983
»
Logged
Xeda112358
they/them
Moderator
LV12
Extreme Poster (Next: 5000)
Posts: 4704
Rating: +719/-6
Calc-u-lator, do doo doo do do do.
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #6 on:
November 09, 2012, 08:30:47 am »
Wow, this looks absolutely intriguing. I cannot yet arrive to this same conclusion, but I have some math that may be of interest. Please note that I figured this all out on my own (including the Euler-Maclaurin formula. I only just recently learned that it was already discovered). Anyways, this does not at all answer your question, but I think you will appreciate this math, especially if you understand the Riemann Zeta function.
Use the Euler-Maclaurin formula to show that:
sum(sin(n),n,0,x)=sum(sin(n),n,1,x)=integral(sin(x))+sin(x)/2+cos(x)/12--cos(x)/(30*4!)+cos(x)/(42*6!)--cos(x)(30*8!)+...
=-|B
0
|cos(x)+|B
1
|sin(x)+|B
2
|cos(x)/2!+|B
4
|cos(x)/4!+|B
6
|cos(x)/6!+|B
8
|cos(x)/8!+|B
10
|cos(x)/10!...
(where B
n
is the Bernoulli numbers)
Then we have that sum(sin(n),n,1,x)=B
1
sin(x)+cos(x)(-B
0
+|B
2
|/2!+|B
4
|/4!+|B
6
|/6!+|B
8
|/8!+...)=B
1
sin(x)-cos(x)+cos(x)sum(|B
2n
|/(2n)!,n,1,x)
To be mathematically tricky, I will make that -cos(x) go into the sum, even though all the other terms are positive. How? Note that 2^0=1, but 2^n, where n is an integer greater than 0 is even. Then, (-1)
2
n
=-1 for n=0 and 1 for all the rest. So:
sum(sin(n),n,1,x)=sin(x)/2+cos(x)sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)
Note that this is a constant: sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)
Now we step completely away from this. How do we write sum(sin(n),n,1,x) in an alternative way? First, look at sum(a
n
,n,0,x)=a
0
+a
1
+a
2
+a
3
+...+a
x
. If we add a
x+1
, we will have the following:
a
x+1
+sum(a
n
,n,0,x)=sum(a
n
,n,0,
x+1
)
Reindexing the right side a few times:
a
x+1
+sum(a
n
,n,0,x)=a
0
+sum(a
n
,n,1,
x+1
)
a
x+1
+sum(a
n
,n,0,x)=1+sum(a
n+1
,n,0,
x
)
Now the sums have the same index, so we can combine them:
a
x+1
-1=sum(a
n+1
,n,0,x)-sum(a
n
,n,0,x)
a
x+1
-1=sum(a
n+1
-a
n
,n,0,x)
a
x+1
-1=sum(a
n
(a-1),n,0,x)
a
x+1
-1=(a-1)sum(a
n
,n,0,x)
(a
x+1
-1)/(a-1)=sum(a
n
,n,0,x)
Now how is this useful? Recall that e
bi
=cos(b)+isin(b) (if you want, I can give a clever little proof of that using the Maclaurin series of e
x
). Then, if we take only the imaginary part of that, we will have sin(b). This means, if we want sin(0)+sin(1)+sin(2)+...+sin(x), we can simply do this:
sum(sin(n),n,0,x)=Im(sum(e
ni
,n,0,x))=Im((e
i(x+1)
-1)/(e
i
-1))
So reindexing, we get:
sum(sin(n),n,1,x)=Im(sum(e
ni
,n,1,x))=Im((e
i(x+1)
-1)/(e
i
-1)-1)
sum(sin(n),n,1,x)=Im(sum(e
ni
,n,1,x))=Im((e
i(x+1)
-1)/(e
i
-1)) (this is because "-1" is not imaginary, so it doesn't matter)
Now we look back
Im((e
i(x+1)
-1)/(e
i
-1))=sin(x)/2+cos(x)sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)
Im((e
i(x+1)
-1)/(cos(x)(e
i
-1)))=tan(x)/2+sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)
Im((e
i(x+1)
-1)/(cos(x)(e
i
-1)))=tan(x)/2+sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)
And all I can get from this is that the constant "sum((-1)
2
n
|B
2n
|/(2n)!,n,0,x)" changes values
This is why I love the Bernoulli numbers when manipulating them with alternating functions.
«
Last Edit: November 09, 2012, 08:35:06 am by Xeda112358
»
Logged
My pastebin
|
Pokémon Amber
|
Grammer Programming Language
|
BatLib Library
|
Jade Simulator
|
Zeda's Hex Opcodes
|
FileSyst Library
|
CopyProg
|
TPROG
|
GroupRead
|
Lbl Read/Write
|
Z80 Floating Point Routines
(
z80float on GitHub
)|
Z80 Optimized Routines Repository
Juju
Incredibly sexy mare
Coder Of Tomorrow
LV13
Extreme Addict (Next: 9001)
Posts: 5730
Rating: +500/-19
Weird programmer
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #7 on:
November 09, 2012, 08:34:43 am »
That's pretty interesting, I should show this to my math teacher. Also we need a prettyprint bbcode, like what Wikipedia have
And you deserve one (1) internet for crashing WolframAlpha.
Logged
Remember the day the walrus started to fly...
I finally cleared
my sig
after 4 years you're happy now?
This signature is ridiculously large you've been warned.
The cute mare that used to be in my avatar is Yuki Kagayaki, you can follow her on
Facebook
and
Tumblr
.
aeTIos
Nonbinary computing specialist
LV12
Extreme Poster (Next: 5000)
Posts: 3915
Rating: +184/-32
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #8 on:
November 09, 2012, 10:52:19 am »
xeda strikes again O.o
Logged
I'm not a nerd but I pretend:
Nosferatu Arucard 1983
LV2
Member (Next: 40)
Posts: 28
Rating: +6/-0
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #9 on:
November 09, 2012, 12:06:46 pm »
I will analyse the Xeda resolution method since it use the Mac-Laurin Equation which is very usefull to calculate former divergent series numerically, just to fill a possible analytic continuation of the function.
OK! Let's show my full resolution!
Using Abel-Plana formula, the original serie is equall to the following integral:
sum(sin(x),x,0,infinity) = integral(sin(x),x,0,infinity) - integral(2*sinh(x)/(exp(2*pi*x)-1),x,0,infinity)
The first one won't make sense (is divergent) unless we apply a renormalization factor:
integral(sin(x),x,0,infinity) = lim t=0 of integral(exp(-t*x)*sin(x),x,0,infinity)
Apply integration by parts twice and solve the equation to the original integral as an unknow:
integral(exp(-t*x)*sin(x),x,0,infinity) = 1 / (1 + t^2)
Then: integral(sin(x),x,0,infinity) = lim t=0 of 1/(1+t^2) = 1
The second integral should be transformed in a series respecting to the denominator, since it is a nicelly absolute convergent integral, this means:
integral(2*sinh(x)/(exp(2*pi*x)-1),x,0,infinity) = - 1* sum of integral(2*sinh(x)*exp(2*pi*x*n),x,0,infinity) from n=0 to infinity
Now the new integral is easylly solved by integration by parts twice, and just apply the same trick just as before, to get:
integral(2*sinh(x)/(exp(2*pi*x)-1),x,0,infinity) = sum of 2/(4*pi^2*n^2 - 1) from n=0 to infinity.
And all this means I coulf convert a divergent series into a new one that is cleary convergent.
sum(sin(x),x,0,infinity) = 1 + sum(2/(4*pi^2*n^2-1),n,0,infinity).
And I will take a break to continue the proof in the next post.
Edit: Oh! I found a little mistake...
«
Last Edit: November 09, 2012, 01:24:55 pm by Nosferatu Arucard 1983
»
Logged
Goplat
LV5
Advanced (Next: 300)
Posts: 289
Rating: +82/-0
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #10 on:
November 09, 2012, 12:29:33 pm »
This sum doesn't converge, but the average value of a finite sum sum(sin(x),x,0,i) is approximately 0.91524, and 2+(1/2)*cotan(1/2) = 2.91524386... I think that 2+ doesn't really belong.
Also, solving the infinite series the easy way (multiply and cancel) gives cot(1/2)/2 without the 2+:
sin(x) = (e^ix - e^-ix)/2i
sum(sin(x),x,0,inf) = (... - e^-3i - e^-2i - e^-i + 0 + e^i + e^2i + e^3i + ...)/2i
sum(sin(x),x,0,inf)*e^(-i/2) = (... - e^(-5i/2) - e^(-3i/2) + 0 + e^(i/2) + e^(3i/2) + e^(5i/2) + ...)/2i
sum(sin(x),x,0,inf)*e^(i/2) = (... - e^(-5i/2) - e^(-3i/2) - e^(-i/2) + 0 + e^(3i/2) + e^(5i/2) + ...)/2i
sum(sin(x),x,0,inf)*(e^(-i/2) - e^(i/2)) = (e^(-i/2) + e^(i/2))/2i
sum(sin(x),x,0,inf)*-2i*sin(1/2) = cos(1/2)/i
sum(sin(x),x,0,inf) = cot(1/2)/2
Logged
+1/-0 karm for this message
Numquam te deseram; numquam te deficiam; numquam circa curram et te desolabo
Numquam te plorare faciam; numquam valedicam; numquam mendacium dicam et te vulnerabo
Nosferatu Arucard 1983
LV2
Member (Next: 40)
Posts: 28
Rating: +6/-0
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #11 on:
November 09, 2012, 12:51:30 pm »
The final clue to solve this problem just needs the Euler Formula of sine:
sin(pi*x) / (pi*x) = product(1-x^2/n^2,n,1,infinity)
Apply the logarithmic derivative of the Euler Formula of sine and you get:
pi*cotan(pi*x) = 1/x + sum(2*x/(x^2-n^2),n,1,infinity)
(This equation is main key to solve the Euler Problem to establish the semi-rational values of Riemann Zeta Function in terms of Bernoulli Numbers
)
This means if I split the series (since n=0 term is absent, so just expand it):
sum(2/(4*pi^2*n^2-1),n,0,infinity) = -2 + sum(2/(4*pi^2*n^2-1),n,1,infinity)
So is just the cotangent series, when it will make clear when split the common terms:
2/(4*pi^2*n^2-1) = 2 / (4 * pi^2 (n^2 - 1/(4 * pi^2)), this means x= -1/2*pi
And so, will get:
-pi*cotan(-1/2) = -(2*pi) - sum (2/(2*pi*(1/(4*x^2)-n^2)
To fix the discripancy, then just divide all terms by (2*pi), and we proofed that:
sum(2/(4*pi^2*n^2-1),n,1,infinity) = 1 - (1/2)*cotan(1/2), since the cotangent is a even function.
And finally at least, we obtain the final formula:
sum(sin(x),x,0,infinity) = 1 +1 - 2 + (1/2)*cotan(1/2) = (1/2)*cotan(1/2)
Edit: Little error detected!
«
Last Edit: November 09, 2012, 01:25:51 pm by Nosferatu Arucard 1983
»
Logged
Xeda112358
they/them
Moderator
LV12
Extreme Poster (Next: 5000)
Posts: 4704
Rating: +719/-6
Calc-u-lator, do doo doo do do do.
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #12 on:
November 09, 2012, 12:59:24 pm »
That is pretty cool o.o
@Goplat: That is brilliant o.o
Logged
My pastebin
|
Pokémon Amber
|
Grammer Programming Language
|
BatLib Library
|
Jade Simulator
|
Zeda's Hex Opcodes
|
FileSyst Library
|
CopyProg
|
TPROG
|
GroupRead
|
Lbl Read/Write
|
Z80 Floating Point Routines
(
z80float on GitHub
)|
Z80 Optimized Routines Repository
pimathbrainiac
Occasionally I make projects
Members
LV10
31337 u53r (Next: 2000)
Posts: 1731
Rating: +136/-23
dagaem
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=(1/2)*cotan(1/2)
«
Reply #13 on:
November 09, 2012, 01:29:21 pm »
* pimathbrainiac is mindblown
Logged
I am Bach.
Nosferatu Arucard 1983
LV2
Member (Next: 40)
Posts: 28
Rating: +6/-0
Re: A Math Challenge: Proof that sum(sin(x),x,0,infinity)=2+(1/2)*cotan(1/2)
«
Reply #14 on:
November 09, 2012, 01:31:20 pm »
After some review, the sum of sin(x) from x=0 to infinity is really (1/2)*cotan(1/2).
Logged
Print
Pages: [
1
]
Go Up
« previous
next »
Omnimaga
»
Forum
»
General Discussion
»
Other Discussions
»
Math and Science
»
A Math Challenge: Proof that sum(sin(x),x,0,infinity)=(1/2)*cotan(1/2)