EV2CDF
      SUBROUTINE EV2CDF(X,GAMMA,CDF)
  
PURPOSE--This subroutine computes the cumulative distribution
         function value for the extreme value type 2
         distribution with single precision tail length
         parameter = GAMMA.  The extreme value type 2
         distribution used herein is defined for all
         non-negative X, and has the probability density
         function
         F(X) = GAMMA * (X**(-GAMMA-1)) * EXP(-(X**(-GAMMA))).
IPUT  ARGUMENTS--X      = The single precision value at which
                          the cumulative distribution  function
                          is to be evaluated.  X should be
                          non-negative.
              --GAMMA  =  The single precision value of the
                          tail length of parameter GAMMA
                          should be positive.
OUTPUT ARGUMENTS--CDF   = The single precision cumulative
                          distribution function value.
OUTPUT--The single precision cumulative distribution function
        value CDF for the extreme value type 2 distribution
        with tail length parameter value = GAMMA.
PRINTING--None unless an input argument error condition exists.
RESTRICTIONS--GAMMA should be positive.
            --X should be non-negative.
OTHER DATAPAC   SUBROUTINES NEEDED--None
FORTRAN LIBRARY SUBROUTINES NEEDED--EXP.
MODE OF INTERNAL OPERATIONS--Single Precision.
LANGUAGE--ANSI FORTRAN.
REFERENCES--Johnson and Kotz, Continuous Univariate
            Distributions--1, 1970, Pages 272-295.
WRITTEN BY--James J. Filliben
            Statistical Engineering Laboratory (205.03)
            National Bureau of Standards
            Gaithersburg, MD  20899
            Phone--  301-921-2315
ORIGINAL VERSION--November  1975.