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/

**Follow-Ups**:**Re: Re: Creating a symmetric matrix***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>

**References**:**Creating a symmetric matrix***From:*Mark Coleman <mark@markscoleman.com>