SUBROUTINE OPEN_MON_TEMP_FILE(LUN)
C----------------------------------------------------------------------
C-
C-   Purpose and Methods : Manage a temporary file for repeated reads and
C-     writes. The first time this routine is called, a file is created with
C-     STATUS='SCRATCH'. If the file is already open when this routine is
C-     called, simply REWIND the file. Calling EOF_MON_TEMP_FILE writes a
C-     FORTRAN end of file marker to the file. Calling CLOSE_MON_TEMP_FILE
C-     closes and deletes the file.
C-
C-   Inputs  : none
C-   Outputs : LUN      The logical unit to use.
C-   Controls: none
C-
C-   Created  14-APR-1992   Philippe Laurens, Steven Klocek
C-
C----------------------------------------------------------------------
      IMPLICIT NONE
C
      INTEGER LUN
      LOGICAL FILE_OPEN, FIRST
      INTEGER SAVELUN
      SAVE FILE_OPEN, FIRST, SAVELUN
      DATA FIRST / .TRUE. /, FILE_OPEN /.FALSE./
C
      PARAMETER FNAME = 'TRGMON_TMP.DAT'
C
      INTEGER IERR
C
      IF (FIRST .EQV. .TRUE.) THEN
        FIRST = .FALSE.
        CALL GTUNIT(521, SAVELUN, IERR)
        IF (IERR .NE. 0) THEN
          CALL ERRMSG('GTUNIT', 'OPEN_MON_TEMP_FILE', 
     &      'Could not allocate unit number', 'F')
        ENDIF
      ENDIF
C
      LUN = SAVELUN
C
      IF (FILE_OPEN .EQV. .TRUE.) THEN
        REWIND LUN
        GOTO 999
      ENDIF
C
      OPEN (UNIT=LUN, FILE=FNAME, ERR=100, STATUS='SCRATCH')
      FILE_OPEN = .TRUE.
      GOTO 999
C
  100 CONTINUE
      CALL ERRMSG('OPEN ERROR', 'OPEN_MON_TEMP_FILE', 
     &  'Could not open file ' // FNAME, 'F')
C----------------------------------------------------------------------
  999 RETURN
C
C
C
      ENTRY EOF_MON_TEMP_FILE
C----------------------------------------------------------------------
C-
C-   Purpose and Methods : Write a FORTRAN end of file record to the current
C-     temporary file.
C-
C-   Inputs  : none
C-   Outputs : file output
C-   Controls: none
C-
C-   Created  14-APR-1992   Philippe Laurens, Steven Klocek
C-
C----------------------------------------------------------------------
      IF (FILE_OPEN .EQV. .TRUE.) THEN
        ENDFILE SAVELUN
        REWIND SAVELUN
      ENDIF
      RETURN
C
C
C
      ENTRY CLOSE_MON_TEMP_FILE
C----------------------------------------------------------------------
C-
C-   Purpose and Methods : Close the temporary file, and clear the flag which
C-     indicates that the file is open. Since the file was opened with
C-     STATUS='SCRATCH', the file should be deleted on close.
C-
C-   Inputs  : none
C-   Outputs : none
C-   Controls: none
C-
C-   Created  14-APR-1992   Philippe Laurens, Steven Klocek
C-
C----------------------------------------------------------------------
      IF (FILE_OPEN .EQV. .TRUE.) THEN
        CLOSE(SAVELUN)
        FILE_OPEN = .FALSE.
      ENDIF
      RETURN
C
      END