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MathGroup Archive 2004

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Re: Creating a symmetric matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46870] Re: Creating a symmetric matrix
  • From: Paul Abbott <paul at physics.uwa.edu.au>
  • Date: Fri, 12 Mar 2004 02:21:50 -0500 (EST)
  • Organization: The University of Western Australia
  • References: <c2p9ld$dns$1@smc.vnet.net> <c2rne4$p04$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <c2rne4$p04$1 at smc.vnet.net>,
 Jens-Peer Kuska <kuska at informatik.uni-leipzig.de> wrote:

> ll = PadRight[#, 4, 0] & /@ Table[a[j, i], {j, 1, 4}, {i, 1, j}];
> ll = ll + MapIndexed[If[Equal @@ #2, 0, #1] & , Transpose[ll], {2}]

How about

  ll = PadRight[#, 4, 0] & /@ Table[a[j, i], {j, 1, 4}, {i, 1, j}];

  ll + Transpose[ll] - DiagonalMatrix[Tr[ll, List]]

instead?

Cheers,
Paul


> Regards
>   Jens
> 
> 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
>

-- 
Paul Abbott                                   Phone: +61 8 9380 2734
School of Physics, M013                         Fax: +61 8 9380 1014
The University of Western Australia      (CRICOS Provider No 00126G)         
35 Stirling Highway
Crawley WA 6009                      mailto:paul at physics.uwa.edu.au 
AUSTRALIA                            http://physics.uwa.edu.au/~paul


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