CDECK  ID>, HWUMAS.

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

*-- Author :    Bryan Webber

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

      SUBROUTINE HWUMAS(P)

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

C     PUTS INVARIANT MASS IN 5TH COMPONENT OF VECTOR

C     (NEGATIVE SIGN IF SPACELIKE)

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

      DOUBLE PRECISION HWUSQR,P(5)

      EXTERNAL HWUSQR

      P(5)=HWUSQR((P(4)+P(3))*(P(4)-P(3))-P(1)**2-P(2)**2)

      END