Actual source code: ex20.c
petsc-3.12.4 2020-02-04
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      2: static char help[] = "Tests converting a matrix to another format with MatConvert().\n\n";

      4:  #include <petscmat.h>

      6: int main(int argc,char **args)
      7: {
      8:   Mat            C,A;
      9:   PetscInt       i,j,m = 5,n = 4,Ii,J;
     11:   PetscMPIInt    rank,size;
     12:   PetscScalar    v;
     13:   char           mtype[256];

     15:   PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
     16:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     18:   /* This example does not work correctly for np > 2 */
     19:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     20:   if (size > 2) SETERRQ(PETSC_COMM_WORLD,1,"Use np <= 2");

     22:   /* Create the matrix for the five point stencil, YET AGAIN */
     23:   MatCreate(PETSC_COMM_WORLD,&C);
     24:   MatSetSizes(C,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);
     25:   MatSetFromOptions(C);
     26:   MatSetUp(C);
     27:   for (i=0; i<m; i++) {
     28:     for (j=2*rank; j<2*rank+2; j++) {
     29:       v = -1.0;  Ii = j + n*i;
     30:       if (i>0)   {J = Ii - n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     31:       if (i<m-1) {J = Ii + n; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     32:       if (j>0)   {J = Ii - 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     33:       if (j<n-1) {J = Ii + 1; MatSetValues(C,1,&Ii,1,&J,&v,INSERT_VALUES);}
     34:       v = 4.0; MatSetValues(C,1,&Ii,1,&Ii,&v,INSERT_VALUES);
     35:     }
     36:   }

     38:   MatAssemblyBegin(C,MAT_FINAL_ASSEMBLY);
     39:   MatAssemblyEnd(C,MAT_FINAL_ASSEMBLY);
     40:   PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO);
     41:   MatView(C,PETSC_VIEWER_STDOUT_WORLD);
     42:   PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD);
     43:   MatView(C,PETSC_VIEWER_STDOUT_WORLD);

     45:   PetscStrcpy(mtype,MATSAME);
     46:   PetscOptionsGetString(NULL,NULL,"-conv_mat_type",mtype,256,NULL);
     47:   MatConvert(C,mtype,MAT_INITIAL_MATRIX,&A);
     48:   PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_INFO);
     49:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);
     50:   PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD);
     51:   PetscViewerPushFormat(PETSC_VIEWER_STDOUT_WORLD,PETSC_VIEWER_ASCII_IMPL);
     52:   MatView(A,PETSC_VIEWER_STDOUT_WORLD);
     53:   PetscViewerPopFormat(PETSC_VIEWER_STDOUT_WORLD);

     55:   /* Free data structures */
     56:   MatDestroy(&A);
     57:   MatDestroy(&C);

     59:   PetscFinalize();
     60:   return ierr;
     61: }

     64: /*TEST

     66:    test:
     67:       args: -conv_mat_type seqaij

     69: TEST*/