Re: Puzzled by Sum

*To*: mathgroup at smc.vnet.net*Subject*: [mg124626] Re: Puzzled by Sum*From*: Shizu <slivo.vitz at msa.hinet.net>*Date*: Fri, 27 Jan 2012 06:10:07 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com

Your logic is right. My experiment: In[]:= A[i_, j_] := i/j + j/i In[]:= Hold[Sum[A[i - j, j], {j, 1, i - 1}]] /. i -> X Out[] = Hold[something] In[]:= F[X_] := something (* Just copy&paste something we obtained above.*) In[]:= F[2] Out[] = 2 Hence, I cannot see the reason your def. doesn't work. ====== The following variations all work tho: In[]:= A[i_, j_] := i/j + j/i In[]:= F[X_] := (Sum[A[X - j, j], {j, 1, X - 1}]) In[]:= F[X_] := Block[{i = X}, Sum[A[i - j, j], {j, 1, i - 1}]] In[]:= F[X_] := (i = X; Sum[A[i - j, j], {j, 1, i - 1}])