incorrect Sum[]
- To: mathgroup at smc.vnet.net
- Subject: [mg107571] incorrect Sum[]
- From: David Bevan <david.bevan at pb.com>
- Date: Wed, 17 Feb 2010 08:03:48 -0500 (EST)
Sum[] gets the following sum wrong:
In[]:= f[n_,k_]:=-((2 (-1)^k n Pochhammer[1-2 n,-1+k])/k!)
Note that f[n,k] is actually the same as Binomial[2n,k].
In[]:= Sum[f[n,k],{k,0,n}]
Out[]= 4^n
In[]:= Sum[f[n,k]/.n->5,{k,0,5}]
Table[f[n,k]/.n->5,{k,0,5}]
Total[%]
Out[]= 638
Out[]= {1,10,45,120,210,252}
Out[]= 638
In[]:= 4^5
Out[]= 1024
It gets the following correct:
In[]:= Sum[f[n,k],{k,0,2n}]
Out[]= 4^n
I've forwarded this to submitabug.
David %^>
David Bevan
Development Manager
Pitney Bowes Emtex Software
Tel: +44 (0)1923 279300
David.Bevan at pb.com