FUNCTION OPEN_MGMT_FILE( UNIT_NUM , FILE_NAME )
C----------------------------------------------------------------------
C-
C-   Purpose and Methods : Opens the specified file, and returns error status
C-
C-   Returned value  : IO status, 0 means no error
C-   Inputs  : UNIT_NUM         IO unit number to be opened
C-             FILE_NAME        The name of the file to be opened
C-   Outputs : 
C-   Controls: 
C-
C-   Created  17-MAY-1990   MICHIGAN STATE UNIVERSITY, TRIGGER CONTROL SOFTWARE
C-
C----------------------------------------------------------------------
      IMPLICIT NONE
C----------------------------------------------------------------------
C
C       Global declarations
C
      INCLUDE 'D0$LEVEL1:PARSE_TOKENS.PARAMS'
      INCLUDE 'D0$LEVEL1:PARSE_TOKENS.INC'
C
C       ARGUMENTS
C
      INTEGER OPEN_MGMT_FILE 
      INTEGER UNIT_NUM 
      CHARACTER*(*) FILE_NAME 
C
C----------------------------------------------------------------------
C       Function
C
      OPEN_MGMT_FILE = 0
C
      IF (VERBOSE) THEN
        WRITE ( 6, 100 ) FILE_NAME
  100   FORMAT ( ' Opening Lookup System Management File ', A )
      ENDIF
C
      OPEN ( UNIT = UNIT_NUM,
     &       FILE = FILE_NAME,
     &       STATUS = 'OLD',            ! File must already exist
     &       BLANK = 'NULL',            ! Blanks are seen as nulls
     &       IOSTAT = OPEN_MGMT_FILE,   ! Return IO status
     &       ERR = 1000 )               ! go on error
      GOTO 9999                         ! return
C
C       error found
C
 1000 CONTINUE
      CALL MESSAGE_OUT(MES_OPEN_FAILED, 0, ' ')
      LSM_IOSTAT = OPEN_MGMT_FILE
C
C---------------------------------------------------------------------------
C
 9999 RETURN
      END