minbound = maxbound = 1;

  tmin = tmax = 0.0;

  if (strcmp(arg[4],"INF") == 0) minbound = 0;

  if (strcmp(arg[4],"NULL") == 0) minbound = 0;

  else tmin = atof(arg[4]);

  if (strcmp(arg[5],"INF") == 0) maxbound = 0;

  if (strcmp(arg[5],"NULL") == 0) maxbound = 0;

  else tmax = atof(arg[5]);

  xmax = atof(arg[6]);

  if (minbound && tmin < 0.0) error->all("Illegal fix dt/reset command");

  if (maxbound && tmax < 0.0) error->all("Illegal fix dt/reset command");

  if (minbound && maxbound && tmin > tmax)

  if (minbound && maxbound && tmin >= tmax)

    error->all("Illegal fix dt/reset command");

  if (xmax <= 0.0) error->all("Illegal fix dt/reset command");

    if ((strcmp(output->dump[i]->style,"dcd") == 0 ||

	strcmp(output->dump[i]->style,"xtc") == 0) && comm->me == 0)

      error->warning("Dump dcd/xtc timestamp may be wrong with fix dt/reset");

  ftm2v = force->ftm2v;

}

/* ---------------------------------------------------------------------- */

void FixDtReset::end_of_step()

{

  double dt,dtv,dtf,dtsq;

  double vsq,fsq,massinv;

  double delx,dely,delz,delr;

  // accumulate total time based on previous timestep

  t_elapsed += (update->ntimestep - laststep) * update->dt;

  int *mask = atom->mask;

  int nlocal = atom->nlocal;

  double vsq,fsq,asq,ms;

  double bound[2],bound_all[2];

  bound[0] = bound[1] = 0.0;

  double dtmin = BIG;

  for (int i = 0; i < nlocal; i++)

    if (mask[i] & groupbit) {

      if (rmass) massinv = 1.0/rmass[i];

      else massinv = 1.0/mass[type[i]];

      vsq = v[i][0]*v[i][0] + v[i][1]*v[i][1] + v[i][2]*v[i][2];

      fsq = f[i][0]*f[i][0] + f[i][1]*f[i][1] + f[i][2]*f[i][2];

      if (rmass) ms = rmass[i];

      else ms = mass[type[i]];

      asq = fsq/ms/ms;

      bound[0] = MAX(bound[0],vsq);

      bound[1] = MAX(bound[1],asq);

      dtv = dtf = BIG;

      if (vsq > 0.0) dtv = xmax/sqrt(vsq);

      if (fsq > 0.0) dtf = sqrt(2.0*xmax/(ftm2v*sqrt(fsq)*massinv));

      dt = MIN(dtv,dtf);

      dtsq = dt*dt;

      delx = dt*v[i][0] + 0.5*dtsq*massinv*f[i][0] * ftm2v;

      dely = dt*v[i][1] + 0.5*dtsq*massinv*f[i][1] * ftm2v;

      delz = dt*v[i][2] + 0.5*dtsq*massinv*f[i][2] * ftm2v;

      delr = sqrt(delx*delx + dely*dely + delz*delz);

      if (delr > xmax) dt *= xmax/delr;

      dtmin = MIN(dtmin,dt);

    }

  MPI_Allreduce(bound,bound_all,2,MPI_DOUBLE,MPI_MAX,world);

  // set new timestep

  double dt,dt1,dt2;

  if (bound_all[0] > 0.0) dt1 = xmax/sqrt(bound_all[0]);

  else dt1 = BIG;

  if (bound_all[1] > 0.0) dt2 = sqrt(2.0 * xmax/sqrt(bound_all[1]));

  else dt2 = BIG;

  MPI_Allreduce(&dtmin,&dt,1,MPI_DOUBLE,MPI_MIN,world);

  dt = MIN(dt1,dt2);

  if (minbound) dt = MAX(dt,tmin);

  if (maxbound) dt = MIN(dt,tmax);

 private:

  int minbound,maxbound,laststep;

  double tmin,tmax,xmax;

  double ftm2v;

  double t_elapsed;

  int respaflag;

};