CALL SEQUENCE...
       zxmav ZXIN ZXOUT OUTPUT
 
 
      DESCRIPTION... 
       ZXMAV  - COMPUTES MERIDIONAL AVERAGE OF ONE CROSS-SECTION 
 
 
      AUTHOR  - J.D.Henderson, Nov. 07/1980.
      LAST REVISION: $Header: /home/cvs/RMNLIB/utils/rdiag/lspgm/zxmav.ptn,v 4.9 2014/09/25 20:20:57 dugas Exp $
 
 
      PURPOSE - READS ONE CROSS-SECTION FROM FILE ZXIN, INTEGRATES IN LATITUDE
                AND PUTS THE RESULTS ON FILE ZXOUT. 
 
      NOTE    - AT INPUT THE CROSS-SECTION IS ORDERED FROM S TO N AND 
                TOP TO BOTTOM. MAXIMUM LATITUDES IS 1999, MAXIMUM LEVELS IS 999. 
 
 
      INPUT FILE... 
       ZXIN  = ONE CROSS-SECTION ON PRESSURE LEVELS 
 
      OUTPUT FILE... 
       ZXOUT = ONE CROSS-SECTION WHERE EACH LEVEL IS SET TO THE MERIDION 
               AVERAGE OF THE CORRESPONDING LEVEL OF ZXIN. 
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 UNABLE TO READ ZXIN
        2 TOO MANY OR NOT ENOUGH LEVELS IN ZXIN
        3 ZXIN IN NOT A ZONAL CROSS-SECTION FILE