CALL SEQUENCE...
       vpint  XIN XOUT OUTPUT [ -def ]
 
 
      DESCRIPTION...
       vpint   - VERTICAL PRESSURE INTEGRAL OF FIELDS IN A FILE
 
 
      AUTHORS  - R.Laprise AND J.D.Henderson, MAY 14 1983.
      LAST REVISION: $Header: Corrections-to-the-detection-of-vertical-intervals-and-a-few-other-minor-changes @ Tue, 21 Mar 2017 14:40:48 -0400 (Bernard Dugas) $
 
 
      PURPOSE  - COMPUTES THE VERTICAL INTEGRATION OF A FILE OF PRESSURE LEVEL
                 SETS USING TRAPEZOIDAL QUADRATURE.
 
      NOTES    - 1) FILE XIN MAY CONTAIN SEVERAL FIELDS.
                 2) MINIMUM NUMBER OF LEVELS IS 2, MAX IS 999.
                    THEY SHOULD ALSO BE VARYING 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 AND BOTTOM
                    ARE GIVEN BY THE FIRST AN LAST DATA LEVEL, RESPECTIVELY.
                    OTHERWISE, VPINT WILL USE 0 AND 101330 PASCALS.
 
 
      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