INTEGER FUNCTION NDISC(N,P)
C  This routine randomly selects one from among N categories, where the 
C  probabilities are proportional to the vector P.
      IMPLICIT REAL*8 (A-H,O-Z)
      DIMENSION P(N)
      DATA CC/1.00000008D0/
      U=DRNUNF()*DSUM(N,P,1)
      AA=0.0D0
      DO 10 I=1,N
      AA=AA+P(I)
      IF(U.LE.AA)GO TO 20
   10 CONTINUE
      IF(U.GT.(AA*CC))GO TO 30
      NDISC=N
      RETURN
   20 NDISC=I
      RETURN
   30 CALL TERM('LIMITS EXCEEDED IN NDISC')
      END