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Re: Adding elements of a matrix

• To: mathgroup at smc.vnet.net
• Subject: [mg40601] Re: Adding elements of a matrix
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 11 Apr 2003 01:59:25 -0400 (EDT)
• Organization: Universitaet Leipzig
• References: <b738oh$o7l$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

m = Table[a[i, j], {i, 3}, {j, 3}];
summand = Table[b[i, j], {i, 3}, {j, 3}];

and

MapIndexed[
  If[Greater @@ #2, #1 + Part[summand, Sequence @@ #2], #1] &, m, {2}]

will increment only the upper triangular part.

Regards
  Jens

Rebeca Choy wrote:
> 
> Hi,
> 
> How can I add in Mathematica every element of a matrix without adding
> twice the mixed terms?
> 
> for example i have a matrix m[[i,j]] and i want to add every term where
> i<j (this is to avoiding adding twice the same number)
> 
> Can I do it with Sum?
> 
> Rebeca Choy

• Follow-Ups:
  • Re: Re: Adding elements of a matrix
    • From: Dr Bob <majort@cox-internet.com>