gcinit.f

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      SUBROUTINE gcinit
*
*
*       Initialization of 3D cluster orbit.
*       -----------------------------------
*
      include 'common6.h'
      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  fd(3),fdd(3)
*
* 
*       Obtain initial force and first derivative from point-mass galaxy.
      IF (gmg.GT.0.0d0) THEN
          rin2 = 1.0/(rg(1)**2 + rg(2)**2 + rg(3)**2)
          rin3 = rin2*sqrt(rin2)
          rgvg = 3.0*(rg(1)*vg(1) + rg(2)*vg(2) + rg(3)*vg(3))*rin2
*     
          DO 1 k = 1,3
              fg(k) = -gmg*rg(k)*rin3
              fgd(k) = -gmg*(vg(k) - rgvg*rg(k))*rin3
    1     CONTINUE
      ELSE
          DO 5 k = 1,3
              fg(k) = 0.0
              fgd(k) = 0.0
    5     CONTINUE
      END IF
*
*      Add possible effect of the bulge (for determining tidal radius).
      IF (gmb.GT.0.0d0) THEN
          CALL fbulge(rg,vg,fd,fdd)
          DO 10 k = 1,3
              fg(k) = fg(k) + fd(k)
              fgd(k) = fgd(k) + fdd(k)
   10     CONTINUE
      END IF
*
*       Include optional disk contribution (may dominate tidal field).
      IF (disk.GT.0.0d0) THEN
          CALL fdisk(rg,vg,fd,fdd)
          DO 15 k = 1,3
              fg(k) = fg(k) + fd(k)
              fgd(k) = fgd(k) + fdd(k)
   15     CONTINUE
      END IF
*
*       Check addition of logarithmic galaxy potential (not linearized).
      IF (v02.GT.0.0d0) THEN
          CALL fhalo(rg,vg,fd,fdd)
          DO 20 k = 1,3
               fg(k) = fg(k) + fd(k)
               fgd(k) = fgd(k) + fdd(k)
   20     CONTINUE
      END IF
*
*       Initialize the time of GC integration.
      tg = time + toff
*
      RETURN
*
      END