2: static char help[] = "Writes a matrix using the PETSc sparse format. Input arguments are:\n\
  3:    -fout <file> : output file name\n\n";

  5:  #include <petscmat.h>

  7: int main(int argc,char **args)
  8: {
  9:   Mat            A;
 10:   Vec            b;
 11:   char           fileout[PETSC_MAX_PATH_LEN];
 12:   PetscInt       i,j,m = 6,n = 6,N = 36,Ii,J;
 14:   PetscScalar    val,v;
 15:   PetscViewer    view;

 17:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
 18:   MatCreate(PETSC_COMM_WORLD,&A);
 19:   MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,N,N);
 20:   MatSetFromOptions(A);
 21:   for (i=0; i<m; i++) {
 22:     for (j=0; j<n; j++) {
 23:       v = -1.0;  Ii = j + n*i;
 24:       if (i>0)   {J = Ii - n; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
 25:       if (i<m-1) {J = Ii + n; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
 26:       if (j>0)   {J = Ii - 1; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
 27:       if (j<n-1) {J = Ii + 1; MatSetValues(A,1,&Ii,1,&J,&v,INSERT_VALUES);}
 28:       v = 4.0; MatSetValues(A,1,&Ii,1,&Ii,&v,INSERT_VALUES);
 29:     }
 30:   }
 31:   MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);
 32:   MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

 34:   VecCreate(PETSC_COMM_WORLD,&b);
 35:   VecSetSizes(b,PETSC_DECIDE,N);
 36:   VecSetFromOptions(b);
 37:   for (i=0; i<N; i++) {
 38:     val  = i + 1;
 39:     VecSetValues(b,1,&i,&val,INSERT_VALUES);
 40:   }
 41:   VecAssemblyBegin(b);
 42:   VecAssemblyEnd(b);

 44:   PetscOptionsGetString(NULL,NULL,"-fout",fileout,PETSC_MAX_PATH_LEN,NULL);
 45:   PetscViewerBinaryOpen(PETSC_COMM_WORLD,fileout,FILE_MODE_WRITE,&view);
 46:   MatView(A,view);
 47:   VecView(b,view);
 48:   PetscViewerDestroy(&view);

 50:   VecDestroy(&b);
 51:   MatDestroy(&A);

 53:   PetscFinalize();
 54:   return ierr;
 55: }