open_files Subroutine

   subroutine open_files
      use global_variables, only: verbose, fileprefix, output_prefix
      use constants, only: nout, mfile
      use process_input, only: nin

      implicit none

      !  Open the input/output external files
      if (trim(fileprefix) == "") then
         open(unit=nin,file="IN.DAT",status='old')
      else
         open(unit=nin,file=trim(fileprefix),status='old')
      end if

      open(unit=nout     ,file=trim(output_prefix)//'OUT.DAT'   ,status='unknown')
      open(unit=mfile    ,file=trim(output_prefix)//'MFILE.DAT' ,status='unknown')

   end subroutine open_files