Re: Simplifying to PolyLog
- To: mathgroup at smc.vnet.net
- Subject: [mg113525] Re: Simplifying to PolyLog
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Mon, 1 Nov 2010 05:00:34 -0500 (EST)
On 10/31/10 at 2:07 AM, sam.takoy at yahoo.com (Sam Takoy) wrote:
>I'm puzzled by the fact that the first of the following expressions
>is successfully summed while the second, simpler one is not:
>In[806]:= Sum[(((-1)^n) (r^n) Cos[a n] )/n^3, {n, 1, Infinity}]
>Sum[(((-1)^n) Cos[a n] )/n^3, {n, 1, Infinity}]
They both sum for me.
In[1]:= Sum[(((-1)^n) (r^n) Cos[a n])/n^3, {n, 1, Infinity}]
Sum[(((-1)^n) Cos[a n])/n^3, {n, 1, Infinity}]
Out[1]= (PolyLog[3, (-E^((-I)*a))*r] +
PolyLog[3, (-E^(I*a))*r])/2
Out[2]= (PolyLog[3, -E^((-I)*a)] + PolyLog[3, -E^(I*a)])/2
In[3]:= $Version
Out[3]= 7.0 for Mac OS X x86 (64-bit) (February 19, 2009)