CDECK  ID>, HWUMBW.

*CMZ :-        -21/02/98  11.11.56  by  Bryan Webber

*-- Author :    Bryan Webber

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

      FUNCTION HWUMBW(ID)

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

C     CHOOSES MASS ACCORDING TO BREIT-WIGNER DISTRIBUTION

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

      INCLUDE 'HERWIG61.INC'

      DOUBLE PRECISION HWUMBW,HWR,WMX,TAU,T

      INTEGER ID

C--WMX IS MAX NUMBER OF WIDTHS FROM NOMINAL MASS

      DATA WMX/10D0/

      SAVE WMX

      HWUMBW=RMASS(ID)

      TAU=RLTIM(ID)

      IF (TAU.EQ.ZERO.OR.TAU.GT.1D-18) RETURN

 1    T=HALF*TAN(PIFAC*(HWR()-HALF))

      IF (ABS(T).GT.WMX) GO TO 1

      HWUMBW=HWUMBW+HBAR*T/TAU

      IF(HWUMBW.LT.ZERO) GOTO 1

      END