EV2PLT
      SUBROUTINE EV2PLT(X,N,GAMMA)
  
PURPOSE--This subroutine generates a extreme value type 2
         probability plot (with tail length parameter value =
         GAMMA).  The prototype extreme value type 2
         distribution used N herein is defined for all
         non-negative x, and has the probability density function
         F(X) = GAMMA * (X**(-GAMMA-1)) * EXP(-(X**(-GAMMA))).
         as used herein, a probability plot for a distribution
         is a plot of the ordered observations versus the order
         statistic medians for that distribution.  The extreme
         value type 2 probability plot is useful in graphically
         testing the composite (that is, location and scale
         parameters need not be specified) hypothesis that the
         underlying distribution from which the data have been
         randomly drawn is the extreme value type 2 distribution
         with tail length parameter value = GAMMA.  if the
         hypothesis is true, the probability plot should be
         near-linear.  A measure of such linearity is given by
         the calculated probability plot correlation
         coefficient.
INPUT  ARGUMENTS--X      = The single precision vector of
                           (unsorted or sorted) observations.
                --N      = The integer number of observations
                           in the vector X.
                --GAMMA  = The single precision value of the
                           tail length parameter.  GAMMA
                           should be positive.
OUTPUT--A one-page extreme value type 2 porbability plot.
PRINTING--Yes.
RESTRICTIONS--The maximum allowable value of N for this
              subroutine is 7500.
            --GAMMA should be positive.
OTHER DATAPAC   SUBROUTINES NEEDED--SORT, UNIMED, PLOT.
FORTRAN LIBRARY SUBROUTINES NEEDED--SQRT, ALOG.
MODE OF INTERNAL OPERATIONS--Single Precision.
LANGUAGE--ANSI FORTRAN.
REFERENCES--Filliben, 'Techniques for Tail Length Analysis',
            Proceedings of the Eighteenth Conference
            on the Design of Experiments Army Research
            Development and Testing (Aberdeen, Maryland,
            October, 1972), Pages 425-450.
          --Hahn and Shaprio, Statistical Methods in Engineering,
            1967, Pages 260-308.
          --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--December  1972.
UPDATED         --September 1975.
UPDATED         --November  1975.
UPDATED         --February  1976.