Coding rule violations corrected.

[u/mrichter/AliRoot.git] / HERWIG / src / hwdrm5.f

CDECK  ID>, HWDRM5.

*CMZ :-        -20/07/99  10:56:12  by  Peter Richardson

*-- Author :    Peter Richardson

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

      SUBROUTINE HWDRM5(X,Y,Z,A,B,MA,MB,MC,MD,MR,GAM)

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

C     Subroutine to find the maximum of the ME

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

      IMPLICIT NONE

      DOUBLE PRECISION X,Y,Z,MA,MB,MC,MD,MR,GAM,RES(3),A,B,C,D,

     &                 E2S,E3S,E2M,E3M,LOW,UPP,HWRUNI,EPS,ZERO

      EXTERNAL HWRUNI

      PARAMETER(EPS=1D-9,ZERO=0)

      C = A**2+B**2

      D = 4*A*B

      RES(1) = -D*(MA**2 + MB**2)*MC*MD +

     &          C*(GAM**2*MR**2 + MR**4 - MA**2*MC**2 - MB**2*MC**2 -

     &          MA**2*MD**2 - MB**2*MD**2)

      RES(2) = (GAM**2*MR**2 + (-MR**2 + MA**2 + MB**2)**2)*

     &          (D**2*MC**2*MD**2 +

     &          2*C*D*MC*MD*(-MR**2 + MC**2 + MD**2) +

     &          C**2*(GAM**2*MR**2 + (-MR**2 + MC**2 + MD**2)**2))

      RES(3) = -D*MC*MD+C*(2*MR**2-(MA**2+MB**2+MC**2+MD**2))

      IF(RES(2).GT.ZERO) THEN

        RES(2) = SQRT(RES(2))

      ELSE

        RES(2) = 0.0D0

      ENDIF

      IF((RES(1)+RES(2))/RES(3).GT.(MD-MC)**2.OR.

     &              (RES(1)+RES(2))/RES(3).LT.(MA+MB)**2) THEN

        X = (RES(1)-RES(2))/RES(3)

      ELSE

        X = (RES(1)+RES(2))/RES(3)

      ENDIF

      IF(X.GT.(MD-MC)**2) X = (MD-MC)**2

      IF(X.LT.(MA+MB)**2) X = (MA+MB)**2

      E2S = (X-MA**2+MB**2)/(2*SQRT(X))

      E3S = (MD**2-X-MC**2)/(2*SQRT(X))

      E2M = E2S**2-MB**2

      E3M = E3S**2-MC**2

      IF(E2M.LT.ZERO) THEN

        IF(ABS(E2M/E2S).GT.EPS) CALL HWWARN('HWDRM5',2,*10)

 10     E2M= 0.0D0

      ENDIF

      IF(E3M.LT.ZERO) THEN

        IF(ABS(E3M/E3S).GT.EPS) CALL HWWARN('HWDRM5',3,*20)

 20     E3M= 0.0D0

      ENDIF

      E2M = SQRT(E2M)

      E3M = SQRT(E3M)

      LOW = (E2S+E3S)**2-(E2M+E3M)**2

      UPP = (E2S+E3S)**2-(E2M-E3M)**2

      Y   = HWRUNI(1,LOW,UPP)

      Z   = MA**2+MB**2+MC**2+MD**2-X-Y

      END