erel3.f

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      SUBROUTINE erel3(IM,EB,SEMI)
*
*
*       Dominant two-body energy in three-body system.
*       ----------------------------------------------
*
      IMPLICIT REAL*8  (a-h,m,o-z)
      common/azreg/  time3,tmax,q(8),p(8),r1,r2,r3,energy,m(3),x3(3,3),
     &               xdot3(3,3),cm(10),c11,c12,c19,c20,c24,c25,
     &               nstep3,name3(3),kz15,kz27
      common/azcoll/  rk(3),qk(8),pk(8),icall,icoll,ndiss3
      REAL*8  p1(8)
*
*
*       Specify KS index for least dominant motion (M(3-IM) & M(3)).
      k = 4*(2 - im)
*
*       Form physical momenta from collision configuration.
      p1(k+1) = qk(k+1)*pk(k+1) - qk(k+2)*pk(k+2) - qk(k+3)*pk(k+3) +
     &                                              qk(k+4)*pk(k+4)
      p1(k+2) = qk(k+2)*pk(k+1) + qk(k+1)*pk(k+2) - qk(k+4)*pk(k+3) -
     &                                              qk(k+3)*pk(k+4)
      p1(k+3) = qk(k+3)*pk(k+1) + qk(k+4)*pk(k+2) + qk(k+1)*pk(k+3) +
     &                                              qk(k+2)*pk(k+4)
*
*       Set distance & physical momentum (eqn (53)).
      ri = qk(k+1)**2 + qk(k+2)**2 + qk(k+3)**2 + qk(k+4)**2
      p1(k+1) = 0.5d0*p1(k+1)/ri
      p1(k+2) = 0.5d0*p1(k+2)/ri
      p1(k+3) = 0.5d0*p1(k+3)/ri
*
*       Form square momentum (c.m. motion of M(IM) & M(3) added below).
      p2 = 0.0d0
      DO 15 j = 1,3
          p2 = p2 + p1(k+j)**2
   15 CONTINUE
*
*       Obtain binding energy from total energy and perturbing function.
      mb = m(im) + m(3)
      mu2 = m(3-im)*mb/(m(3-im) + mb)
      vp = 0.5d0*p2/mu2 - m(1)*m(2)/r3 - m(3-im)*m(3)/max(r1,r2)
      eb = 0.5d0*energy - vp
*
*       Set semi-major axis.
      semi = -m(im)*m(3)/(2.0d0*eb)
*
      RETURN
*
      END