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.
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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}])