Actual source code: ex4.c

      1: /*
      2:   Contributed by: Fande Kong
      3:  */

      5: static char help[] = "Illustrate the use of MatResetPreallocation.\n";

      7: #include <petscmat.h>

      9: int main(int argc, char **argv)
     10: {
     11:   Mat      A;
     12:   MPI_Comm comm;
     13:   PetscInt n = 5, m = 5, *dnnz, *onnz, i, rstart, rend, M, N;

     15:   PetscFunctionBeginUser;
     16:   PetscCall(PetscInitialize(&argc, &argv, 0, help));
     17:   comm = MPI_COMM_WORLD;
     18:   PetscCall(PetscMalloc2(m, &dnnz, m, &onnz));
     19:   for (i = 0; i < m; i++) {
     20:     dnnz[i] = 1;
     21:     onnz[i] = 1;
     22:   }
     23:   PetscCall(MatCreateAIJ(comm, m, n, PETSC_DETERMINE, PETSC_DETERMINE, PETSC_DECIDE, dnnz, PETSC_DECIDE, onnz, &A));
     24:   PetscCall(MatSetFromOptions(A));
     25:   PetscCall(MatSetUp(A));
     26:   PetscCall(PetscFree2(dnnz, onnz));

     28:   /* since the matrix has never been assembled this reset should do nothing */
     29:   PetscCall(MatResetPreallocation(A));

     31:   /* This assembly shrinks memory because we do not insert enough number of values */
     32:   PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
     33:   PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));

     35:   /* MatResetPreallocation() restores the memory required by users */
     36:   PetscCall(MatResetPreallocation(A));
     37:   PetscCall(MatSetOption(A, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_TRUE));
     38:   PetscCall(MatGetOwnershipRange(A, &rstart, &rend));
     39:   PetscCall(MatGetSize(A, &M, &N));
     40:   for (i = rstart; i < rend; i++) {
     41:     PetscCall(MatSetValue(A, i, i, 2.0, INSERT_VALUES));
     42:     if (rend < N) PetscCall(MatSetValue(A, i, rend, 1.0, INSERT_VALUES));
     43:   }
     44:   PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
     45:   PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
     46:   PetscCall(MatView(A, PETSC_VIEWER_STDOUT_WORLD));
     47:   PetscCall(MatDestroy(&A));
     48:   PetscCall(PetscFinalize());
     49:   return 0;
     50: }

     52: /*TEST

     54:    test:
     55:       suffix: 1

     57:    test:
     58:       suffix: 2
     59:       nsize: 2

     61: TEST*/