static const char help[] = "Test MatGetLocalSubMatrix() with multiple levels of nesting.\n\n";

#include <petscmat.h>

int main(int argc, char *argv[])
{
  IS             is0a,is0b,is0,is1,isl0a,isl0b,isl0,isl1;
  Mat            A,Aexplicit;
  PetscBool      usenest;
  PetscMPIInt    rank,size;
  PetscInt       i,j;

  PetscCall(PetscInitialize(&argc,&argv,NULL,help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank));
  PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD,&size));

  {
    PetscInt ix0a[1],ix0b[1],ix0[2],ix1[1];

    ix0a[0] = rank*2+0;
    ix0b[0] = rank*2+1;
    ix0[0]  = rank*3+0; ix0[1] = rank*3+1;
    ix1[0]  = rank*3+2;
    PetscCall(ISCreateGeneral(PETSC_COMM_WORLD,1,ix0a,PETSC_COPY_VALUES,&is0a));
    PetscCall(ISCreateGeneral(PETSC_COMM_WORLD,1,ix0b,PETSC_COPY_VALUES,&is0b));
    PetscCall(ISCreateGeneral(PETSC_COMM_WORLD,2,ix0,PETSC_COPY_VALUES,&is0));
    PetscCall(ISCreateGeneral(PETSC_COMM_WORLD,1,ix1,PETSC_COPY_VALUES,&is1));
  }
  {
    PetscCall(ISCreateStride(PETSC_COMM_SELF,6,0,1,&isl0));
    PetscCall(ISCreateStride(PETSC_COMM_SELF,3,0,1,&isl0a));
    PetscCall(ISCreateStride(PETSC_COMM_SELF,3,3,1,&isl0b));
    PetscCall(ISCreateStride(PETSC_COMM_SELF,3,6,1,&isl1));
  }

  usenest = PETSC_FALSE;
  PetscCall(PetscOptionsGetBool(NULL,NULL,"-nest",&usenest,NULL));
  if (usenest) {
    ISLocalToGlobalMapping l2g;
    PetscInt               l2gind[3];
    Mat                    B[9];

    l2gind[0] = (rank-1+size)%size; l2gind[1] = rank; l2gind[2] = (rank+1)%size;
    PetscCall(ISLocalToGlobalMappingCreate(PETSC_COMM_WORLD,1,3,l2gind,PETSC_COPY_VALUES,&l2g));
    for (i=0; i<9; i++) {
      PetscCall(MatCreateAIJ(PETSC_COMM_WORLD,1,1,PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,NULL,PETSC_DECIDE,NULL,&B[i]));
      PetscCall(MatSetUp(B[i]));
      PetscCall(MatSetLocalToGlobalMapping(B[i],l2g,l2g));
    }
    {
      IS  isx[2];
      Mat Bx00[4],Bx01[2],Bx10[2];
      Mat B00,B01,B10;

      isx[0]  = is0a; isx[1] = is0b;
      Bx00[0] = B[0]; Bx00[1] = B[1]; Bx00[2] = B[3]; Bx00[3] = B[4];
      Bx01[0] = B[2]; Bx01[1] = B[5];
      Bx10[0] = B[6]; Bx10[1] = B[7];

      PetscCall(MatCreateNest(PETSC_COMM_WORLD,2,isx,2,isx,Bx00,&B00));
      PetscCall(MatSetUp(B00));
      PetscCall(MatCreateNest(PETSC_COMM_WORLD,2,isx,1,NULL,Bx01,&B01));
      PetscCall(MatSetUp(B01));
      PetscCall(MatCreateNest(PETSC_COMM_WORLD,1,NULL,2,isx,Bx10,&B10));
      PetscCall(MatSetUp(B10));
      {
        Mat By[4];
        IS  isy[2];

        By[0]  = B00; By[1] = B01; By[2] = B10; By[3] = B[8];
        isy[0] = is0; isy[1] = is1;

        PetscCall(MatCreateNest(PETSC_COMM_WORLD,2,isy,2,isy,By,&A));
        PetscCall(MatSetUp(A));
      }
      PetscCall(MatDestroy(&B00));
      PetscCall(MatDestroy(&B01));
      PetscCall(MatDestroy(&B10));
    }
    for (i=0; i<9; i++) PetscCall(MatDestroy(&B[i]));
    PetscCall(ISLocalToGlobalMappingDestroy(&l2g));
  } else {
    ISLocalToGlobalMapping l2g;
    PetscInt               l2gind[9];
    for (i=0; i<3; i++) for (j=0; j<3; j++) l2gind[3*i+j] = ((rank-1+j+size) % size)*3 + i;
    PetscCall(ISLocalToGlobalMappingCreate(PETSC_COMM_WORLD,1,9,l2gind,PETSC_COPY_VALUES,&l2g));
    PetscCall(MatCreateAIJ(PETSC_COMM_WORLD,3,3,PETSC_DECIDE,PETSC_DECIDE,PETSC_DECIDE,NULL,PETSC_DECIDE,NULL,&A));
    PetscCall(MatSetLocalToGlobalMapping(A,l2g,l2g));
    PetscCall(ISLocalToGlobalMappingDestroy(&l2g));
  }

  {
    Mat A00,A11,A0a0a,A0a0b;
    PetscCall(MatGetLocalSubMatrix(A,isl0,isl0,&A00));
    PetscCall(MatGetLocalSubMatrix(A,isl1,isl1,&A11));
    PetscCall(MatGetLocalSubMatrix(A00,isl0a,isl0a,&A0a0a));
    PetscCall(MatGetLocalSubMatrix(A00,isl0a,isl0b,&A0a0b));

    PetscCall(MatSetValueLocal(A0a0a,0,0,100*rank+1,ADD_VALUES));
    PetscCall(MatSetValueLocal(A0a0a,0,1,100*rank+2,ADD_VALUES));
    PetscCall(MatSetValueLocal(A0a0a,2,2,100*rank+9,ADD_VALUES));

    PetscCall(MatSetValueLocal(A0a0b,1,1,100*rank+50+5,ADD_VALUES));

    PetscCall(MatSetValueLocal(A11,0,0,1000*(rank+1)+1,ADD_VALUES));
    PetscCall(MatSetValueLocal(A11,1,2,1000*(rank+1)+6,ADD_VALUES));

    PetscCall(MatRestoreLocalSubMatrix(A00,isl0a,isl0a,&A0a0a));
    PetscCall(MatRestoreLocalSubMatrix(A00,isl0a,isl0b,&A0a0b));
    PetscCall(MatRestoreLocalSubMatrix(A,isl0,isl0,&A00));
    PetscCall(MatRestoreLocalSubMatrix(A,isl1,isl1,&A11));
  }
  PetscCall(MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY));

  PetscCall(MatComputeOperator(A,MATAIJ,&Aexplicit));
  PetscCall(MatView(Aexplicit,PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(MatDestroy(&A));
  PetscCall(MatDestroy(&Aexplicit));
  PetscCall(ISDestroy(&is0a));
  PetscCall(ISDestroy(&is0b));
  PetscCall(ISDestroy(&is0));
  PetscCall(ISDestroy(&is1));
  PetscCall(ISDestroy(&isl0a));
  PetscCall(ISDestroy(&isl0b));
  PetscCall(ISDestroy(&isl0));
  PetscCall(ISDestroy(&isl1));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 3

   test:
      suffix: nest
      nsize: 3
      args: -nest

TEST*/