int main(int argc,char **args)
{
Mat A1,A2,A3,A4,nest;
Mat mata[4];
Mat aij;
MPI_Comm comm;
PetscInt m,n,istart,iend,ii,i,J,j;
PetscScalar v;
PetscMPIInt size;
PetscErrorCode ierr;
ierr = PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
comm = PETSC_COMM_WORLD;
ierr = MPI_Comm_size(comm,&size);CHKERRQ(ierr);
/*
Assemble the matrix for the five point stencil, YET AGAIN
*/
ierr = MatCreate(comm,&A1);CHKERRQ(ierr);
m=2,n=2;
ierr = MatSetSizes(A1,PETSC_DECIDE,PETSC_DECIDE,m*n,m*n);CHKERRQ(ierr);
ierr = MatSetFromOptions(A1);CHKERRQ(ierr);
ierr = MatSetUp(A1);CHKERRQ(ierr);
ierr = MatGetOwnershipRange(A1,&istart,&iend);CHKERRQ(ierr);
for (ii=istart; ii<iend; ii++) {
v = -1.0; i = ii/n; j = ii - i*n;
if (i>0) {J = ii - n; ierr = MatSetValues(A1,1,&ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
if (i<m-1) {J = ii + n; ierr = MatSetValues(A1,1,&ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
if (j>0) {J = ii - 1; ierr = MatSetValues(A1,1,&ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
if (j<n-1) {J = ii + 1; ierr = MatSetValues(A1,1,&ii,1,&J,&v,INSERT_VALUES);CHKERRQ(ierr);}
v = 4.0; ierr = MatSetValues(A1,1,&ii,1,&ii,&v,INSERT_VALUES);CHKERRQ(ierr);
}
ierr = MatAssemblyBegin(A1,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
ierr = MatAssemblyEnd(A1,MAT_FINAL_ASSEMBLY);CHKERRQ(ierr);
ierr = MatView(A1,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = MatDuplicate(A1,MAT_COPY_VALUES,&A2);CHKERRQ(ierr);
ierr = MatDuplicate(A1,MAT_COPY_VALUES,&A3);CHKERRQ(ierr);
ierr = MatDuplicate(A1,MAT_COPY_VALUES,&A4);CHKERRQ(ierr);
/*create a nest matrix */
ierr = MatCreate(comm,&nest);CHKERRQ(ierr);
ierr = MatSetType(nest,MATNEST);CHKERRQ(ierr);
mata[0]=A1,mata[1]=A2,mata[2]=A3,mata[3]=A4;
ierr = MatNestSetSubMats(nest,2,NULL,2,NULL,mata);CHKERRQ(ierr);
ierr = MatSetUp(nest);CHKERRQ(ierr);
ierr = MatConvert(nest,MATAIJ,MAT_INITIAL_MATRIX,&aij);CHKERRQ(ierr);
ierr = MatView(aij,PETSC_VIEWER_STDOUT_WORLD);CHKERRQ(ierr);
ierr = MatDestroy(&nest);CHKERRQ(ierr);
ierr = MatDestroy(&aij);CHKERRQ(ierr);
ierr = MatDestroy(&A1);CHKERRQ(ierr);
ierr = MatDestroy(&A2);CHKERRQ(ierr);
ierr = MatDestroy(&A3);CHKERRQ(ierr);
ierr = MatDestroy(&A4);CHKERRQ(ierr);
ierr = PetscFinalize();
return ierr;
}
void PETSC_STDCALL matnestsetsubmats_(Mat A,PetscInt *nr, IS is_row[],PetscInt *nc, IS is_col[], Mat a[], int *__ierr ){
*__ierr = MatNestSetSubMats(
(Mat)PetscToPointer((A) ),*nr,is_row,*nc,is_col,a);
}
