C***********************************************************************
C   THIS SUBROUTINE COMPUTES THE VALUE OF THE CHI(1) PROBABILITY INTEGRA
C   TRANSFORMATION.  SERIES EXPANSION IF THE INTEGRAND IS USED
C   FOLLOWED BY PIECEWISE INTEGRATION. IF Z IS GREATER THAN 20 THE TRUE
C   VALUE OF P IS GREATER THAN .9999
C
C   CALLING ARGUMENTS:
C   Z    THE CHI(1) VALUE
C   P    THE PROBABILITY OF OBSERVING A CHI-SQUARE VALUE ON 1 DEGREE
C        LESS THAN OR EQUAL TO Z. IF Z IS NEGATIVE P IS RETURNED =-1.
C***********************************************************************
      SUBROUTINE ONE (Z,P)
      DATA PI /.564189583/
      P=-1.
      IF (Z.LT.0.) RETURN
      P=1.
      IF (Z.GT.20.) RETURN
      Z2=Z*.5
      A=SQRT(Z2)*PI
      I=0
      S=2.
      FAC=1.
   10 I=I+1
      Q=P
      FAC=-FAC*Z2/FLOAT(I)
      S=S+FAC/(FLOAT(I)+.5)
      P=A*S
      IF (ABS(P-Q).LT..000001) RETURN
      IF (I.GT.50) RETURN
      GO TO 10
      END