CALL SEQUENCE...
       vpintl  XIN XOUT OUTPUT [ -def ]
 
 
      DESCRIPTION...
       vpintl  - VERTICAL PRESSURE INTEGRAL OF FIELDS LEVEL BY LEVEL
 
 
      AUTHOR   - D.Neelin, MAY 14 1983.
      LAST REVISION: $Header: Corrections-a-FSTMDIAG-LININT-VPINTL-et-modifs-a-FSTTRI @ Tue, 10 Oct 2017 16:25:24 -0400 (dugas) $
 
 
      PURPOSE - VERTICAL INTEGRATION OF A FILE OF PRESSURE LEVEL SETS.
                THE RESULTS ARE SAVED LEVEL BY LEVEL AND THE QUADRATURE
                RULE IS TRAPEZOIDAL.
 
      NOTE    - 1) THE FILE XIN MAY CONTAIN SEVERAL FIELDS.
                2) LEVELS SHOULD VARY MONOTONICALLY.
                3) THE PROGRAM ACTUALLY CALCULATES INT( XIN(P) DP/G ),
                   WHICH BY THE HYDROSTATIC APPROXIMATION IS VERY
                   CLOSE TO A VERTICAL MASS INTEGRAL.
                4) WHEN THE -def KEY IS SPECIFIED, THE DOMAIN TOP
                   IS GIVEN BY THE FIRST DATA LEVEL. OTHERWISE,
                   VPINTL WILL USE 0.
 
 
 
      INPUT FILE...
       XIN = FILE OF PRESSURE LEVEL SETS
 
      OUTPUT FILE...
       XOUT = VERTICAL PRESSURE INTEGRALS OF THE SETS IN XIN.
 
 
      EXIT CONDITIONS...
        0 NO PROBLEMS
        1 NOT ENOUGH OR TOO MANY LEVELS IN FIRST SET OF XIN
        2 MORE THAN ONE SIZE FOR ARRAYS IN XIN
        3 NOT ENOUGH LEVELS IN LAST SET READ
        4 LEVELS DO NOT VARY MONOTONICALLY
        5 XIN DOES NOT CONTAIN PRESSURE LEVELS