! $Id$
!------------------------------------------------------------------------------
!S+
! NAME:
!       get_lun
!
! PURPOSE:
!       PUBLIC function to obtain a free logical unit number for file access
!
! CALLING SEQUENCE:
!       result = get_lun()
!
! INPUT ARGUMENTS:
!       None.
!
! OUTPUT ARGUMENTS:
!       None.
!
! FUNCTION RESULT:
!       Function returns a default integer that can be used as a logical unit
!       number to open and access a file.
!
! CALLS:
!       None.
!
! EXTERNALS:
!       None
!
! COMMON BLOCKS:
!       None.
!
! SIDE EFFECTS:
!       None known.
!
! RESTRICTIONS:
!       None.
!
! PROCEDURE:
!       The search for a free logical unit number begins at 10. The logical
!       unit number if tested to see if it is connected to an open file. If
!       so, it is incremented by 1. This is repeated until a free logical
!       unit number is found.
!S-
!------------------------------------------------------------------------------
  FUNCTION get_lun() RESULT( lun )


    ! -----------------
    ! Type declarations
    ! -----------------
 
    INTEGER :: lun
    LOGICAL :: file_open


    ! --------------------------------------------
    ! Initialise logical unit number and file_open
    ! --------------------------------------------

    lun = 9
    file_open = .TRUE.


    ! ------------------------------
    ! Start open loop for lun search
    ! ------------------------------

    lun_search: DO

      ! -- Increment logical unit number
      lun = lun + 1

      ! -- Check if file is open
      INQUIRE( lun, OPENED = file_open )

      ! -- Is this lun available?
      IF ( .NOT. file_open ) EXIT lun_search

    END DO lun_search

  END FUNCTION get_lun