CALL SEQUENCE...
       zxgam  ZXIN ZXOUT OUTPUT [-def]
 
 
      DESCRIPTION...
       zxgam  - CROSS-SECTION GAMMA CALCULATION  GAM=K/(-P*DT/DP+KT) 
 
 
      AUTHOR  - J.D.Henderson, NOV 1980.
      LAST REVISION: $Header: /home/cvs/RMNLIB/utils/rdiag/lspgm/zxgam.ptn,v 4.9 2014/09/25 20:20:57 dugas Exp $
 
 
      PURPOSE - READS TEMPERATURE CROSS-SECTIONS FROM FILE ZXIN, 
                CALCULATES GAMMA FOR EACH LEVEL USING: 
                      GAMMA = K/(-P*DT/DP + K*T) 
                WHERE, 
                      K=RGAS/CP,  T=MERIDIONAL MEAN TEMPERATURE 
                AND PUTS THE RESULT ON FILE ZXOUT. 
 
 
      INPUT FILE... 
       ZXIN  = TEMPERATURE CROSS-SECTIONS ON PRESSURE LEVELS
 
      OUTPUT FILE... 
       ZXOUT = GAMMA CROSS-SECTION 
 
 
      NOTE THAT WHEN THE "-def" COMMAND-LINE PARAMETRE IS SPECIFIED,
      THE PROGRAMS USES A WEIGHTED ALGORITHM WHILE CALCULATING ITS
      VERTICAL DERIVATIVE, TAKING INTO ACCOUNT THE POSSIBLY UN-EVEN
      LEVEL SPACING, SO THAT THE SCHEME BECOMES SECOND-ORDER ACCURATE.
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 TOO MANY OR NOT ENOUGH LEVELS IN ZXIN
        2 FOUND DATA TYPE NOT ZONAL
        3 ABORT ERROR READING ZXIN
        4 LEVELS DO NOT VARY MONOTONICALLY
        5 ZXIN NOT ON PRESSURE LEVELS