CDECK  ID>, HWUECM.

*CMZ :-        -29/01/93  11.11.55  by  Bryan Webber

*-- Author :    Giovanni Abbiendi & Luca Stanco

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

      FUNCTION HWUECM (S,M1QUAD,M2QUAD)

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

C     C.M. ENERGY OF A PARTICLE IN 1-->2 BRANCH, MAY BE SPACELIKE

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

      DOUBLE PRECISION HWUECM,S,M1QUAD,M2QUAD

      HWUECM = (S+M1QUAD-M2QUAD)/(2.D0*SQRT(S))

      END