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MathGroup Archive 1999

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Multiple sum with iterators that cannot equal

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19378] Multiple sum with iterators that cannot equal
  • From: Eric Spahr <rspahr at worldnet.att.net>
  • Date: Sat, 21 Aug 1999 00:04:45 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

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\)\+\(i
!= 
          j\)\) \(w\_i\) \(w\_j\) \[Sigma]\_\(i, j\)\)
    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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