timestep_control.cc

// ---------------------------------------------------------------------
//
// Copyright (C) 2006 - 2019 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE.md at
// the top level directory of deal.II.
//
// ---------------------------------------------------------------------


#include <deal.II/algorithms/timestep_control.h>

#include <deal.II/base/parameter_handler.h>

DEAL_II_NAMESPACE_OPEN

using namespace Algorithms;

TimestepControl::TimestepControl(double start,
                                 double final,
                                 double tolerance,
                                 double start_step,
                                 double print_step,
                                 double max_step)
  : start_val(start)
  , final_val(final)
  , tolerance_val(tolerance)
  , strategy_val(uniform)
  , start_step_val(start_step)
  , max_step_val(max_step)
  , min_step_val(0)
  , current_step_val(start_step)
  , step_val(start_step)
  , print_step(print_step)
  , next_print_val(print_step > 0. ? start_val + print_step : start_val - 1.)
{
  now_val = start_val;
  strcpy(format, "T.%06.3f");

  // avoid compiler warning
  (void)min_step_val;
}



void
TimestepControl::declare_parameters(ParameterHandler &param)
{
  param.declare_entry("Start", "0.", Patterns::Double());
  param.declare_entry("Final", "1.", Patterns::Double());
  param.declare_entry("First step", "1.e-2", Patterns::Double());
  param.declare_entry("Max step", "1.", Patterns::Double());
  param.declare_entry("Tolerance", "1.e-2", Patterns::Double());
  param.declare_entry("Print step", "-1.", Patterns::Double());
  param.declare_entry("Strategy",
                      "uniform",
                      Patterns::Selection("uniform|doubling"));
}



void
TimestepControl::parse_parameters(ParameterHandler &param)
{
  start(param.get_double("Start"));
  start_step(param.get_double("First step"));
  max_step(param.get_double("Max step"));
  final(param.get_double("Final"));
  tolerance(param.get_double("Tolerance"));
  print_step                 = param.get_double("Print step");
  const std::string strategy = param.get("Strategy");
  if (strategy == std::string("uniform"))
    strategy_val = uniform;
  else if (strategy == std::string("doubling"))
    strategy_val = doubling;
}



bool
TimestepControl::advance()
{
  bool   changed = false;
  double s       = step_val;

  // Do time step control, but not in
  // first step.
  if (now_val != start())
    {
      if (strategy_val == doubling && 2 * s <= tolerance_val)
        s *= 2;
      if (s > max_step_val)
        s = max_step_val;
    }

  // Try incrementing time by s
  double h = now_val + s;
  changed  = s != step_val;

  step_val         = s;
  current_step_val = s;
  // If we just missed the final
  // time, increase the step size a
  // bit. This way, we avoid a very
  // small final step. If the step
  // shot over the final time, adjust
  // it so we hit the final time
  // exactly.
  double s1 = .01 * s;
  if (h > final_val - s1)
    {
      current_step_val = final_val - now_val;
      h                = final_val;
      changed          = true;
    }

  now_val = h;
  return changed;
}


bool
TimestepControl::print()
{
  if (print_step == 0.)
    return false;
  if (print_step < 0.)
    return true;

  bool result = (now_val >= next_print_val);

  if (result)
    {
      next_print_val += print_step;
      if (next_print_val > final_val)
        next_print_val = final_val;
    }
  return result;
}

DEAL_II_NAMESPACE_CLOSE