CALL SEQUENCES...
       gpvtat  GHUM GVT GTEMP OUTPUT (1)
       gptavt  GHUM GTEMP GVT OUTPUT (2)
 
 
      DESCRIPTIONS...
       (1) gpvtat  - COMPUTES TEMPERATURE FROM VT AND SHUM
       (2) gptavt  - COMPUTES VIRTUAL TEMPERATURE FROM TEMP AND SHUM
 
 
      AUTHOR  - B.Dugas, RPN: mar 1999.
      LAST REVISION: $Header: Ajouter-l-option-FREEFMT-de-lecture-des-niveaux-suite-2 @ 2018-11-18 18:00:09 -0500 (dugas) $
 
 
      PURPOSE - (1) CONVERTS GRIDS OF SPECIFIC HUMIDITY
                    AND VIRTUAL TEMPERATURE TO TEMPERATURE
                (2) CONVERTS GRIDS OF SPECIFIC HUMIDITY
                    AND TEMPERATURE TO VIRTUAL TEMPERATURE
 
 
      INPUT FILES...
       GHUM      = SPECIFIC HUMIDITY   (VARIABLE NAME 'SHUM' OR 'HU')
       (1) GVT   = VIRTUAL TEMPERATURE (VARIABLE NAME 'VT')
       (2) GTEMP = TEMPERATURE         (VARIABLE NAME 'TEMP' OR 'TT')
 
      OUTPUT FILE...
       (1) GTEMP = TEMPERATURE.
       (2) GVT   = VIRTUAL TEMPERATURE.
 
 
      NOTES: 1) USES THE RPN PHYSIC'S SET OF THERMODYNAMIC
                CONVERSION FUNCTIONS (I.E. FINTERN). THE
                FUNCTION USED HERE IS INDEPENDANT OF
                THE TYPE OF VERTICAL COORDINATE
             2) THE ASSUMED UNITS FOR GVT ARE EITHER CENTIGRADES
                (FOR RPN/CMC FILES) OR KELVINS (FOR CCCma FILES).
             3) WORKS AS WELL ON MODEL LEVELS.
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 UNABLE TO READ FIRST RECORDS IN INPUT FILES
        2 FOUND DATA OTHER THAN TYPE 'GRID' OR 'SUBA'
        3 HUMIDITY VARIABLE NAME NOT RECOGNIZED (NOT 'HU' OR 'SHUM')
        4 PREMATURE EOF ON HUMIDITY FILE 
        5 PREMATURE EOF ON INPUT TEMPERATURE FILE 
        6 HUMIDITY AND TEMPERATURE ARRAYS NOT THE SAME SIZE
        7 TEMPERATURE VARIABLE NAME NOT RECOGNIZED (NOT 'TT' OR 'TEMP')
        8 VIRTUAL TEMPERATURE VARIABLE NAME NOT RECOGNIZED (NOT 'VT')