Actual source code: ex8.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Tests automatic allocation of matrix storage space.\n\n";

      4: #include <petscmat.h>

      8: int main(int argc,char **args)
      9: {
     10:   Mat            C;
     11:   PetscInt       i,j,m = 3,n = 3,Ii,J;
     13:   PetscScalar    v;
     14:   MatInfo        info;

     16:   PetscInitialize(&argc,&args,(char*)0,help);
     17:   PetscOptionsGetInt(NULL,"-m",&m,NULL);
     18:   PetscOptionsGetInt(NULL,"-n",&n,NULL);

     20:   /* create the matrix for the five point stencil, YET AGAIN */
     21:   MatCreate(PETSC_COMM_SELF,&C);
     22:   MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);
     23:   MatSetFromOptions(C);
     24:   MatSetUp(C);
     25:   for (i=0; i<m; i++) {
     26:     for (j=0; j<n; j++) {
     27:       v = -1.0;  Ii = j + n*i;
     28:       if (i>0)   {J=Ii-n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     29:       if (i<m-1) {J=Ii+n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     30:       if (j>0)   {J=Ii-1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     31:       if (j<n-1) {J=Ii+1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     32:       v = 4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,INSERT_VALUES);
     33:     }
     34:   }
     35:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
     36:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
     37:   MatView(C,PETSC_VIEWER_STDOUT_SELF);

     39:   MatGetInfo(C,MAT_LOCAL,&info);
     40:   PetscPrintf(PETSC_COMM_SELF,"matrix nonzeros = %D, allocated nonzeros = %D\n",
     41:                      (PetscInt)info.nz_used,(PetscInt)info.nz_allocated);

     43:   MatDestroy(&C);
     44:   PetscFinalize();
     45:   return 0;
     46: }