      SUBROUTINE WEIPPF(P,GAMMA,PPF)
C
C     PURPOSE--THIS SUBROUTINE COMPUTES THE PERCENT POINT
C              FUNCTION VALUE FOR THE WEIBULL
C              DISTRIBUTION WITH SINGLE PRECISION 
C              TAIL LENGTH PARAMETER = GAMMA.
C              THE WEIBULL DISTRIBUTION USED
C              HEREIN IS DEFINED FOR ALL POSITIVE X,
C              AND HAS THE PROBABILITY DENSITY FUNCTION
C              F(X) = GAMMA * (X**(GAMMA-1)) * EXP(-(X**GAMMA)).
C              NOTE THAT THE PERCENT POINT FUNCTION OF A DISTRIBUTION 
C              IS IDENTICALLY THE SAME AS THE INVERSE CUMULATIVE
C              DISTRIBUTION FUNCTION OF THE DISTRIBUTION.
C     INPUT  ARGUMENTS--P      = THE SINGLE PRECISION VALUE 
C                                (BETWEEN 0.0 (INCLUSIVELY) 
C                                AND 1.0 (EXCLUSIVELY))
C                                AT WHICH THE PERCENT POINT 
C                                FUNCTION IS TO BE EVALUATED.
C                     --GAMMA  = THE SINGLE PRECISION VALUE 
C                                OF THE TAIL LENGTH PARAMETER.
C                                GAMMA SHOULD BE POSITIVE.
C     OUTPUT ARGUMENTS--PPF    = THE SINGLE PRECISION PERCENT
C                                POINT FUNCTION VALUE.
C     OUTPUT--THE SINGLE PRECISION PERCENT POINT FUNCTION . 
C             VALUE PPF FOR THE WEIBULL DISTRIBUTION
C             WITH TAIL LENGTH PARAMETER VALUE = GAMMA.
C     PRINTING--NONE UNLESS AN INPUT ARGUMENT ERROR CONDITION EXISTS. 
C     RESTRICTIONS--GAMMA SHOULD BE POSITIVE.
C                 --P SHOULD BE BETWEEN 0.0 (INCLUSIVELY)
C                   AND 1.0 (EXCLUSIVELY).
C     OTHER DATAPAC   SUBROUTINES NEEDED--NONE.
C     FORTRAN LIBRARY SUBROUTINES NEEDED--ALOG.
C     MODE OF INTERNAL OPERATIONS--SINGLE PRECISION.
C     LANGUAGE--ANSI FORTRAN. 
C     REFERENCES--JOHNSON AND KOTZ, CONTINUOUS UNIVARIATE
C                 DISTRIBUTIONS--1, 1970, PAGES 250-271.
C               --HASTINGS AND PEACOCK, STATISTICAL
C                 DISTRIBUTIONS--A HANDBOOK FOR
C                 STUDENTS AND PRACTITIONERS, 1975,
C                 PAGE 124.
C     WRITTEN BY--JAMES J. FILLIBEN
C                 STATISTICAL ENGINEERING LABORATORY (205.03)
C                 NATIONAL BUREAU OF STANDARDS
C                 WASHINGTON, D. C. 20234
C                 PHONE:  301-921-2315
C     ORIGINAL VERSION--NOVEMBER  1975. 
C
C---------------------------------------------------------------------
C
      IPR=6
C
C     CHECK THE INPUT ARGUMENTS FOR ERRORS
C
      IF(P.LT.0.0.OR.P.GE.1.0)GOTO50
      IF(GAMMA.LE.0.0)GOTO55
      GOTO90
   50 WRITE(IPR,1)
      WRITE(IPR,46)P
      PPF=0.0
      RETURN
   55 WRITE(IPR,15) 
      WRITE(IPR,46)GAMMA
      PPF=0.0
      RETURN
   90 CONTINUE
    1 FORMAT(1H ,115H***** FATAL ERROR--THE FIRST  INPUT ARGUMENT TO THE
     1 WEIPPF SUBROUTINE IS OUTSIDE THE ALLOWABLE (0,1) INTERVAL *****)
   15 FORMAT(1H , 91H***** FATAL ERROR--THE SECOND INPUT ARGUMENT TO THE
     1 WEIPPF SUBROUTINE IS NON-POSITIVE *****)
   46 FORMAT(1H , 35H***** THE VALUE OF THE ARGUMENT IS ,E15.8,6H *****)
C
C-----START POINT-----------------------------------------------------
C
      PPF=(-ALOG(1.0-P))**(1.0/GAMMA)
C
      RETURN
      END 
