tchain.f

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      SUBROUTINE tchain(ISUB,TSMIN)
*
*
*       Time interval for next chain perturber or c.m.
*       ----------------------------------------------
*
      include 'common6.h'
      common/chainc/  xc(3,ncmax),uc(3,ncmax),bodyc(ncmax),ich,
     &                listc(lmax)
      common/clump/   bodys(ncmax,5),t0s(5),ts(5),steps(5),rmaxs(5),
     &                names(ncmax,5),isys(5)
*
*
*       Include chain c.m. in time-step search.
      npc = listc(1) + 2
      listc(npc) = ich
      tsmin = 100.0
      timec = ts(isub)
*
*       Determine time of next chain perturber or c.m. itself.
      DO 10 l = 2,npc
          j = listc(l)
          tsj = t0(j) + step(j)
          tsmin = min(tsmin,tsj - timec)
   10 CONTINUE
*
*       Impose half curent step as minimum time interval.
      tsmin = max(tsmin,0.5d0*step(ich))
*
*       Include safety check for large c.m. step (TPREV = TBLOCK first time).
      IF (tblock.GT.tprev) THEN
          tsmin = min(tsmin,tblock - tprev)
      ELSE
          tsmin = min(tsmin,dtmin)
      END IF
*
*       Specify next interval unless termination.
      IF (steps(isub).GT.0.0d0) THEN
          steps(isub) = tsmin
      END IF
*
      RETURN
*
      END