Re: Bug in Sum?

*To*: mathgroup at smc.vnet.net*Subject*: [mg109146] Re: Bug in Sum?*From*: "Tony Harker" <a.harker at ucl.ac.uk>*Date*: Mon, 19 Apr 2010 04:11:26 -0400 (EDT)

What version are you using? 7.0 for Microsoft Windows (32-bit) (February 18, 2009) gives identical, correct, results for both. Tony Harker ]-> -----Original Message----- ]-> From: gopher [mailto:gophergoon at gmail.com] ]-> Sent: 13 April 2010 04:04 ]-> To: mathgroup at smc.vnet.net ]-> Subject: [mg109109] Bug in Sum? ]-> ]-> In the following, A and Expand[A] give different answers after when ]-> summed (a finite geometric series.) The result of summing A ]-> is clearly ]-> wrong, since it is independent of the parameters r and s. ]-> ]-> Abhishek ]-> ]-> In[44]:= A = x^(i - n) (x^(i - n) (1 - r x^n) - s); ]-> A == Expand[A] // Simplify ]-> ]-> Out[45]= True ]-> ]-> In[46]:= Sum[A, {i, 0, n - 1}] ]-> ]-> Out[46]= (x^(-2 n) (-1 + x^(2 n)))/(-1 + x^2) ]-> ]-> In[47]:= Sum[Expand[A], {i, 0, n - 1}] // FullSimplify ]-> ]-> Out[47]= -(( ]-> x^(-2 n) (-1 + x^n) (-1 + x^n (-1 + r + s + s x + r ]-> x^n)))/(-1 + x^2) ]-> ) ]-> ]->