mp_max_d Subroutine

      SUBROUTINE mp_max_d (msg, gid)
      !! Finds the maximum of a datum with the result left on all processes.
      !!
      !! MPI mapping
      !! mpi_allreduce

         REAL(kind=real_8), INTENT(INOUT)                 :: msg
         !! Find maximum among these data (input) and maximum (output)
         INTEGER, INTENT(IN)                      :: gid
         !! Message passing environment identifier

         CHARACTER(LEN=*), PARAMETER :: routineN = 'mp_max_d'

         INTEGER                                  :: handle, ierr, msglen

         ierr = 0
         CALL timeset(routineN, handle)

         msglen = 1
#if defined(__parallel)
         CALL mpi_allreduce(MPI_IN_PLACE, msg, msglen, MPI_DOUBLE_PRECISION, MPI_MAX, gid, ierr)
         IF (ierr /= 0) CALL mp_stop(ierr, "mpi_allreduce @ "//routineN)
         CALL add_perf(perf_id=3, msg_size=msglen*real_8_size)
#else
         MARK_USED(msg)
         MARK_USED(gid)
#endif
         CALL timestop(handle)
      END SUBROUTINE mp_max_d