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MathGroup Archive 1999

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Re: Multiple sum with iterators that cannot equal

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19621] Re: Multiple sum with iterators that cannot equal
  • From: Mark Fisher <mefisher at bellsouth.net>
  • Date: Sun, 5 Sep 1999 16:57:42 -0400
  • References: <7pl714$cgd@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

If you have version 4, you can use (1-KroneckerDelta[i, j]) to kill off
the terms you don't want.

--Mark

Eric Spahr wrote:
> 
> Using  multiple summmation signs with condition 'i "not
> equal" j', evaluation stops immediately as 'i' starts as
> 1 as does 'j'.  My formula requires that the 'i's' and
> 'j's' together:
> 
>         Sum[Sum[f,{j,1,n}],{i,1,n}] ignore cases where i = j.
> 
>         Or as copied from my notebook:
> 
> \!\(\(\(\[Sum]\+\(i = 1\)\%n\[Sum]\+\(j = 1\)\%n\)\+\(i
> != j\)\) \(w\_i\)
>     w\_j\)
> 
> How do I solve this without some cumbersome loops.
> 
> Many Thanks
> 
> Eric Spahr
> Cottage Technology      rspahr at worldnet.att.net


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