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MathGroup Archive 2006

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Re: creating a symbolic square symmetric matrix

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66336] Re: creating a symbolic square symmetric matrix
  • From: Heinz Spindler <heinz at mathematik.Uni-Osnabrueck.DE>
  • Date: Wed, 10 May 2006 06:33:26 -0400 (EDT)
  • Organization: Universitaet Hannover
  • References: <e3pege$ifq$1@smc.vnet.net>
  • Reply-to: Heinz.Spindler at mathematik.Uni-Osnabrueck.DE
  • Sender: owner-wri-mathgroup at wolfram.com

ravi wrote:

>Hi,
>First, I created a square matrix with the following command :
>n=4;
>mat=Table[Subscript[a,i, j],{i,n},{j,n}]
>In the same style, I would like to create a symmetric matric where all
>a[i, j] is replaced by a[j,i] for i>j. For i<=j, the coefficients
>remain in place.
>I tried to use the replace command :
>Replace[mat,Subscript[a,i,j]->Subscript[a,j,i]]
>This just interchanged the elements. I want this replacement only for
>the lower or upper triangular matrix elements.
>Would appreciate tips of doing a conditional substitution.
>/ravi
>  
>
hi, use the condition  " /;i>j " in the definition of your symmetric matrix

Subscript[a,i_,j_]/;i>j:=Subscript[a,j,i]

mat[n_]:=Table[Subscript[a,i,j],{i,n},{j,n}] 

example: 
mat[3]//MatrixForm



Heinz Spindler


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