Re: How to construct symmetric matrix from just a one
- To: mathgroup at smc.vnet.net
- Subject: [mg110375] Re: How to construct symmetric matrix from just a one
- From: Daniel Lichtblau <danl at wolfram.com>
- Date: Wed, 16 Jun 2010 05:36:23 -0400 (EDT)
dragec wrote:
> please help me with simple to apply function that will construct
> symmetric matrix from given just a half matrix with diagonal.
> Eg:
>
> From:
> 1 0 0 0
> 2 3 0 0
> 4 9 5 0
> 2 2 3 4
>
> To give:
>
> 1 2 4 2
> 2 3 9 2
> 4 9 5 3
> 2 2 3 4
Any of these should do the job.
symmetrize1[mat_] := mat + Transpose[mat] -
DiagonalMatrix[Diagonal[mat]]
symmetrize2[mat_] := With[{n=Length[mat]},
Table[If[i<j,mat[[j,i]],mat[[i,j]]], {i,n}, {j,n}]]
symmetrize3[mat_] := With[{n=Length[mat]},
Table[Join[mat[[i,1;;i]],mat[[i+1;;n,i]]], {i,n}]]
Daniel Lichtblau
Wolfram Research