Status: New
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 3703 by [email protected]: Sum of a finite power series
performs automatic reduction which is not always valid
http://code.google.com/p/sympy/issues/detail?id=3703
Suppose you do:
mysum = summation( ((-1**n)/factorial(2*n+1)) * (x**(4*n+2)) ,(n,1,M) )
print summation.subs(x,1).subs(M,10).doit()
this returns "nan" (not a number), when it should return
(1^1)+(1^2)+...(1^10)=10.
This happens because upon entering it, the sum automatically reduces to:
(x - x**(M + 1))/(-x + 1)
Which is not a valid reduction when x=1.
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