steps.f

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      SUBROUTINE steps(I1,I2)
*
*
*       Initialization of time-steps & prediction variables.
*       ----------------------------------------------------
*
      include 'common6.h'
      REAL*8  fdum(3)
*
*
*       Set new steps and initialize prediction variables.
      DO 40 i = i1,i2
*
*       Include regular force in the irregular step (cf. Makino & SJA 1992).
          DO 5 k = 1,3
              fdum(k) = fi(k,i) + fr(k,i)
    5     CONTINUE
*
*       Determine irregular and regular steps by the general criterion.
          dt = tstep(fdum,d1(1,i),d2(1,i),d3(1,i),etai)
          dtr = tstep(fr(1,i),d1r(1,i),d2r(1,i),d3r(1,i),etar)
*
*       Reduce irregular step for case of triple, quad, chain or merger.
          IF (iphase.GE.4) dt = 0.5*dt
*
*       Initialize the times and obtain discrete steps (block-step version).
          t0(i) = time
          t0r(i) = time
*
*       Convert predicted step to nearest block time-step (truncated down).
          CALL stepk(dt,dtn)
          CALL stepk(dtr,dtrn)
          IF (time.LE.0.0d0) THEN
              step(i) = dtn
              stepr(i) = dtrn
          ELSE 
*       Reduce steps by factor 2 until commensurate with current time.
              step(i) = dtn
              stepr(i) = dtrn
              iter = 0
   10         IF (dmod(time,step(i)).NE.0.0d0) THEN
                  step(i) = 0.5d0*step(i)
                  iter = iter + 1
                  IF (iter.LT.16.OR.step(i).GT.dtk(40)) go to 10
                  step(i) = dtk(40)
                  WRITE (6,15)  i, iter, time/step(i), dt, step(i)
   15             FORMAT (' WARNING!   I ITER T/STEP DT STEP ',
     &                                 i5,i4,f16.4,1p,2e9.1)
              END IF
              iter = 0
   18         IF (dmod(time,stepr(i)).NE.0.0d0) THEN
                  stepr(i) = 0.5d0*stepr(i)
                  iter = iter + 1
                  IF (iter.LT.16.OR.stepr(i).GT.dtk(40)) go to 18
                  stepr(i) = dtk(40)
                  WRITE (6,20)  i, iter, time/stepr(i), dtr, stepr(i)
   20             FORMAT (' WARNING!   I ITER T/STEPR DTR STEPR ',
     &                                 i5,i4,f16.4,1p,2e9.1)
              END IF
          END IF
*
*       Reduce irregular step if STEPR < STEP.
   25 IF (stepr(i).LT.step(i)) THEN
          step(i) = 0.5d0*step(i)
          go to 25
      END IF
*
*       Initialize or update array for new block times.
          tnew(i) = t0(i) + step(i)
*         IF (TIME.GT.0.0) THEN
*             WRITE (7,28)  I, NAME(I), TIME, DT, STEP(I), STEPR(I)
* 28          FORMAT (' STEPS:   I NM TIME DT STEP DTR ',
*    &                           2I5,F12.6,1P,3E9.1)
*             CALL FLUSH(7)
*         END IF
*
*       Set prediction variables (X0DOT set by START, KSREG or KSTERM).
          DO 30 k = 1,3
              x0(k,i) = x(k,i)
              f(k,i) = 0.5d0*f(k,i)
              fdot(k,i) = one6*fdot(k,i)
   30     CONTINUE
   40 CONTINUE
*
      RETURN
*
      END