[petsc-users] Product of nonsymmetric matrices is symmetric

[flw at rzg.mpg.de]

Dear PETSc team,
I have a linear system of the form
A*x=b,
where
A=(D-G^T  D  G).
Here, G and D are real NxN matrices, D is diagonal and G is not  
symmetric. So far, we are using the matmpiaij format for all of the  
given matrices and create A with the help of matmatmult.

  However, as is easy to show, the matrix A itself is symmetric, due  
to the sandwich G^T D G. Therefore, we would like to make use of this  
fact and use the mpisbaij format fir A instead of mpiaij. Can you tell  
me how to set up the matrix A in this fashion? Unfortunately, I  
haven't found anything on that in the archive yet.


Best regards,
Felix