CDECK  ID>, HWURAP.

*CMZ :-        -26/04/91  11.11.56  by  Bryan Webber

*-- Author :    Bryan Webber

C-----------------------------------------------------------------------

      FUNCTION HWURAP(P)

C-----------------------------------------------------------------------

C     LONGITUDINAL RAPIDITY (SET TO +/-1000 IF TOO LARGE)

C-----------------------------------------------------------------------

      DOUBLE PRECISION HWURAP,EMT2,P(5),ZERO

      PARAMETER (ZERO=0.D0)

      EMT2=P(1)**2+P(2)**2+P(5)**2

      IF (P(3).GT.ZERO) THEN

        IF (EMT2.EQ.ZERO) THEN

          HWURAP=1000.

        ELSE

          HWURAP= 0.5*LOG((P(3)+P(4))**2/EMT2)

        ENDIF

      ELSEIF (P(3).LT.ZERO) THEN

        IF (EMT2.EQ.ZERO) THEN

          HWURAP=-1000.

        ELSE

          HWURAP=-0.5*LOG((P(3)-P(4))**2/EMT2)

        ENDIF

      ELSE

          HWURAP=0.

      ENDIF

      END