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MathGroup Archive 2004

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Re: Creating a symmetric matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46857] Re: [mg46853] Creating a symmetric matrix
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Fri, 12 Mar 2004 02:02:42 -0500 (EST)
  • References: <200403110850.DAA13986@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 11 Mar 2004, at 09:50, Mark Coleman wrote:

> Greetings,
>
> How can I efficiently build a symmetric matrix from an upper triangular
> one, i.e., extract the upper triangular elements and insert them into
> the lower triangle in such a way as to make the resulting square matrix
> symmetric?
>
> Thanks,
>
> Mark
>
>
>

The most natural way must be

A+Tranpose[A]

e.g.

A = Array[KroneckerDelta[#1 < #2, True] & , {3, 3}];


{{0, 1, 1}, {0, 0, 1}, {0, 0, 0}}


A + Transpose[A]


{{0, 1, 1}, {1, 0, 1}, {1, 1, 0}}



Andrzej Kozlowski
Chiba, Japan
http://www.mimuw.edu.pl/~akoz/


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