fnuc.f

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      SUBROUTINE fnuc(XI,XIDOT,FM,FD)
*
*
*       Galaxy point-mass force.
*       ------------------------
*
      IMPLICIT REAL*8  (a-h,o-z)
      common/galaxy/ gmg,rg(3),vg(3),fg(3),fgd(3),tg,
     &               omega,disk,a,b,v02,rl2,gmb,ar,gam,zdum(7)
      REAL*8  xi(3),xidot(3),fm(3),fd(3)
*
*
*       Evaluate force and first derivative from global variables.
      r2 = xi(1)**2 + xi(2)**2 + xi(3)**2
      rrd = 3.0*(xi(1)*xidot(1) + xi(2)*xidot(2) + xi(3)*xidot(3))/r2
      h3 = gmg/(r2*sqrt(r2))
*
      DO 10 k = 1,3
          fm(k) = -h3*xi(k)
          fd(k) = -h3*(xidot(k) - rrd*xi(k))
   10 CONTINUE
*
      RETURN
*
      END