incremental_function.cc

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// -----------------------------------------------------------------------------
//
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception OR LGPL-2.1-or-later
// Copyright (C) 2018 - 2026 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Detailed license information governing the source code and contributions
// can be found in LICENSE.md and CONTRIBUTING.md at the top level directory.
//
// -----------------------------------------------------------------------------
 
#include <deal.II/base/incremental_function.h>
#include <deal.II/base/signaling_nan.h>
 
#include <deal.II/lac/vector.h>
 
#include <complex>
 
DEAL_II_NAMESPACE_OPEN
 
namespace Functions
{
  template <int dim, typename RangeNumberType>
  IncrementalFunction<dim, RangeNumberType>::IncrementalFunction(
    Function<dim, RangeNumberType> &base)
    : Function<dim, RangeNumberType>(base.n_components)
    , base(base)
    , delta_t(numbers::signaling_nan<time_type>())
    , values_old(base.n_components)
  {}
 
 
 
  template <int dim, typename RangeNumberType>
  void
  IncrementalFunction<dim, RangeNumberType>::set_decrement(
    const time_type delta)
  {
    Assert(delta >= 0.0,
           ExcMessage("The decrement must be set to a non-negative value."));
    delta_t = delta;
  }
 
 
 
  template <int dim, typename RangeNumberType>
  RangeNumberType
  IncrementalFunction<dim, RangeNumberType>::value(
    const Point<dim>  &p,
    const unsigned int comp) const
  {
    // since we modify a mutable member variable, lock the
    // the data via a mutex
    std::scoped_lock lock(mutex);
 
    // Cache the time state of the base class in case it has been changed
    // within the user code. We reset the wrapped function to the original
    // state once we're done with our own evaluations.
    const auto orig_time = base.get_time();
 
    base.set_time(this->get_time());
    const RangeNumberType current = base.value(p, comp);
 
    base.set_time(this->get_time() - delta_t);
    const RangeNumberType old = base.value(p, comp);
 
    // Reset wrapped function time setting
    base.set_time(orig_time);
 
    return current - old;
  }
 
 
 
  template <int dim, typename RangeNumberType>
  void
  IncrementalFunction<dim, RangeNumberType>::vector_value(
    const Point<dim>        &p,
    Vector<RangeNumberType> &values) const
  {
    // since we modify a mutable member variable, lock the
    // the data via a mutex
    std::scoped_lock lock(mutex);
 
    // Cache the time state of the base class in case it has been changed
    // within the user code. We reset the wrapped function to the original
    // state once we're done with our own evaluations.
    const auto orig_time = base.get_time();
 
    base.set_time(this->get_time());
    base.vector_value(p, values);
 
    base.set_time(this->get_time() - delta_t);
    base.vector_value(p, values_old);
 
    values -= values_old;
 
    // Reset wrapped function time setting
    base.set_time(orig_time);
  }
 
 
// Explicit instantiations
#include "base/incremental_function.inst"
} // namespace Functions
DEAL_II_NAMESPACE_CLOSE