Actual source code: ex14.c
petsc-3.4.2 2013-07-02

      2: static char help[] = "Tests sequential and parallel MatGetRow() and MatRestoreRow().\n";

      4: #include <petscmat.h>

      8: int main(int argc,char **args)
      9: {
     10:   Mat               C;
     11:   PetscInt          i,j,m = 5,n = 5,Ii,J,nz,rstart,rend;
     12:   PetscErrorCode    ierr;
     13:   PetscMPIInt       rank;
     14:   const PetscInt    *idx;
     15:   PetscScalar       v;
     16:   const PetscScalar *values;

     18:   PetscInitialize(&argc,&args,(char*)0,help);

     20:   /* Create the matrix for the five point stencil, YET AGAIN */
     21:   MatCreate(PETSC_COMM_WORLD,&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_WORLD);

     39:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
     40:   MatGetOwnershipRange(C,&rstart,&rend);
     41:   for (i=rstart; i<rend; i++) {
     42:     MatGetRow(C,i,&nz,&idx,&values);
     43:     if (!rank) {
     44:       for (j=0; j<nz; j++) {
     45:         PetscPrintf(PETSC_COMM_SELF,"%D %G ",idx[j],PetscRealPart(values[j]));
     46:       }
     47:       PetscPrintf(PETSC_COMM_SELF,"\n");
     48:     }
     49:     MatRestoreRow(C,i,&nz,&idx,&values);
     50:   }

     52:   MatDestroy(&C);
     53:   PetscFinalize();
     54:   return 0;
     55: }