program test

#include "petsc/finclude/petscsys.h"
  use petscsys
  implicit none

  MPI_Comm :: SUBCOMM
  PetscMPIInt :: size, rank, subrank, subsize, nproc_per_sub
  PetscMPIInt :: nsubs, sub
  PetscViewer :: subOutput
  PetscErrorCode :: ioerr, ierr

  character(len=200) :: cstring, ologfile, seed
  character(len=12) :: x1

  PetscMPIInt, parameter :: i0=0


  ! Initialize Petsc
  call PetscInitialize(PETSC_NULL_CHARACTER,ierr)


  ioerr = 0
  nsubs = 2
  seed='tst'
  x1='01'

  call MPI_Comm_size(PETSC_COMM_WORLD,size,ierr)
  call MPI_Comm_rank(PETSC_COMM_WORLD,rank,ierr)

  if (mod(size, nsubs) /= 0) then
    cstring='The total number of MPI processes is not a multiple of nsubcomm\n\n'
    call PetscPrintf(PETSC_COMM_WORLD,TRIM(cstring),ierr)
    ioerr = 1
    goto 999
  end if
  
  ! Initiate sub-communicators
  nsubs = min(size,nsubs)
  nproc_per_sub = size / nsubs
  sub = min(rank / nproc_per_sub, nsubs - 1)

  ! Create subcommunicator and get team ranks
  call MPI_Comm_split(PETSC_COMM_WORLD, sub, i0, SUBCOMM, ierr)
  call MPI_Comm_rank(SUBCOMM,subrank,ierr)
  call MPI_Comm_size(SUBCOMM,subsize,ierr)

  if (nsubs < 10) then
    write(x1,'(I1.1)') sub+1
  elseif (nsubs < 100)  then
    write(x1,'(I2.2)') sub+1
  elseif (nsubs < 1000)  then
    write(x1,'(I3.3)') sub+1
  else
    write(x1,'(I10)') sub+1
  end if

  ologfile=TRIM(seed)//'_subcomm_'//TRIM(ADJUSTL(x1))//'.log'

  call PetscViewerASCIIOpen(SUBCOMM,TRIM(ologfile),subOutput,ierr)
  call MPI_Allreduce(ierr, ioerr, 1, MPIU_INTEGER, MPI_SUM, PETSC_COMM_WORLD, ierr)
  if (ioerr /= 0) then
    cstring='Unable to open log files, please check folder/file permissions\n\n'
    call PetscPrintf(PETSC_COMM_WORLD,TRIM(cstring),ierr)
    goto 999  
  end if 


  999 continue


  ! finalize petsc
  call PetscFinalize(ierr)

  end program test