!
!   This program demonstrates use of MatCreateSubMatrices() from Fortran
!
      program main
#include <petsc/finclude/petscmat.h>
      use petscmat
      implicit none

      Mat             A,B(2)
      PetscErrorCode  ierr
      PetscInt        nis,zero(1)
      PetscViewer     v
      IS              isrow
      PetscMPIInt     rank

      PetscCallA(PetscInitialize(ierr))
      PetscCallMPIA(MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr))

#if defined(PETSC_USE_64BIT_INDICES)
      PetscCallA(PetscViewerBinaryOpen(PETSC_COMM_WORLD,'${PETSC_DIR}/share/petsc/datafiles/matrices/' // 'ns-real-int64-float64',FILE_MODE_READ,v,ierr))
#else
      PetscCallA(PetscViewerBinaryOpen(PETSC_COMM_WORLD,'${PETSC_DIR}/share/petsc/datafiles/matrices/' // 'ns-real-int32-float64',FILE_MODE_READ,v,ierr))
#endif

      PetscCallA(MatCreate(PETSC_COMM_WORLD,A,ierr))
      PetscCallA(MatSetType(A, MATAIJ,ierr))
      PetscCallA(MatLoad(A,v,ierr))

      nis     = 1
      zero(1) = 0
      if (rank .eq. 1) then
         nis = 0 ! test nis = 0
      endif
      PetscCallA(ISCreateGeneral(PETSC_COMM_SELF,nis,zero,PETSC_COPY_VALUES,isrow,ierr))

      PetscCallA(MatCreateSubmatrices(A,nis,isrow,isrow,MAT_INITIAL_MATRIX,B,ierr))

      if (rank .eq. 0) then
         PetscCallA(MatView(B(1),PETSC_VIEWER_STDOUT_SELF,ierr))
      endif

      PetscCallA(MatCreateSubmatrices(A,nis,isrow,isrow,MAT_REUSE_MATRIX,B,ierr))

      if (rank .eq. 0) then
         PetscCallA(MatView(B(1),PETSC_VIEWER_STDOUT_SELF,ierr))
      endif

      PetscCallA(ISDestroy(isrow,ierr))
      PetscCallA(MatDestroy(A,ierr))
      PetscCallA(MatDestroySubMatrices(nis,B,ierr))
      PetscCallA(PetscViewerDestroy(v,ierr))

      PetscCallA(PetscFinalize(ierr))
      end

!/*TEST
!
!     test:
!        requires: double !complex
!
!TEST*/