[petsc-users] MatSetValues for nonzeros of a sparse matrix

Umut Tabak u.tabak at tudelft.nl
Wed Jan 13 09:16:06 CST 2010

Dear all,

I am reading some FE system matrices from a commercial FE code. I wrote 
an interface where I export them in matrix market format. Also I keep 
the row and column indices of the non-zero values and as well the 
non-zeros values in arrays of proper type.

The question which I could not conclude is that how to use MatSetValues 
for sparse matrix assignments, I mean should I keep all the 
values(non-zeros also) in my inputs?( There are also some pointers for 
block assignments but they work in the same way I guess)

I have tested with the below code. If I supply only the non-zero 
diagonal entries, I get the first row set as expected but this did not 
seem so practical to me, because to get what I want accomplished I 
should keep all the zero entries as well. And I thought that there 
should be a far more efficient way to apply this. (Diagonal assignment 
is just an example.) I am sorry if this question is too naive :)

Any comments is appreciated.
Best regards,

   Mat            A;             /* linear system matrix */
   PetscErrorCode ierr;
   PetscInt       n = 4;
   PetscInt       rI=0,cI=0;
   PetscViewer    viewer;
   PetscInt index;
   // row indices,m column indices,n of Matrix A
   const int idxm[] = { 0,1,2,3 };
   const int idxn[] = { 0,1,2,3 };
   // values in the matrix A, row major order
   PetscScalar valuesMat[]={ 1,0,0,0,0,2,0,0,0,0,3,0,0,0,0,4 };
   //PetscScalar valuesMat[]={ 1,2,3,4 };
   /* should be the 1st call after the declaration and definition
    * block
   PetscInitialize(&argc,&args,(char *)0,help);
   // added by U.Tabak
   // intermediate assigments are
   // set the values of the Matrix A
   ierr = MatSetValues(A, n, idxm, n, idxn, valuesMat,INSERT_VALUES); 
   // done so the 2nd argument should be
   ierr = 
   ierr = 
   ierr = 
   ierr = PetscFinalize();CHKERRQ(ierr);
   return 0;

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