1: /*
  2:  *
  3:  *  Created on: Sep 25, 2017
  4:  *      Author: Fande Kong
  5:  */

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

  9: #include "petscmat.h"

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

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

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

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

 37:   /* MatResetPreallocation() restores the memory required by users */
 38:   PetscCall(MatResetPreallocation(A));
 39:   PetscCall(MatSetOption(A, MAT_NEW_NONZERO_ALLOCATION_ERR, PETSC_TRUE));
 40:   PetscCall(MatGetOwnershipRange(A, &rstart, &rend));
 41:   PetscCall(MatGetSize(A, &M, &N));
 42:   for (i = rstart; i < rend; i++) {
 43:     PetscCall(MatSetValue(A, i, i, 2.0, INSERT_VALUES));
 44:     if (rend < N) PetscCall(MatSetValue(A, i, rend, 1.0, INSERT_VALUES));
 45:   }
 46:   PetscCall(MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY));
 47:   PetscCall(MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY));
 48:   PetscCall(MatView(A, PETSC_VIEWER_STDOUT_WORLD));
 49:   PetscCall(MatDestroy(&A));
 50:   PetscCall(PetscFinalize());
 51:   return 0;
 52: }

 54: /*TEST

 56:    test:
 57:       suffix: 1

 59:    test:
 60:       suffix: 2
 61:       nsize: 2

 63: TEST*/