Actual source code: ex4.c
petsc-3.13.6 2020-09-29
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      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;
     16:   PetscErrorCode  ierr;

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

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

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

     53: /*TEST

     55:    test:
     56:       suffix: 1

     58:    test:
     59:       suffix: 2
     60:       nsize: 2

     62: TEST*/