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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2018 - 2023 by the deal.II authors
//
// This file is part of the deal.II library.
//
// Part of the source code is dual licensed under Apache-2.0 WITH
// LLVM-exception OR LGPL-2.1-or-later. Detailed license information
// governing the source code and code contributions can be found in
// LICENSE.md and CONTRIBUTING.md at the top level directory of deal.II.
//
// ------------------------------------------------------------------------
#ifndef dealii_incremental_function_h
#define dealii_incremental_function_h
#include <deal.II/base/config.h>
#include <deal.II/base/function.h>
#include <deal.II/base/mutex.h>
#include <deal.II/lac/vector.h>
DEAL_II_NAMESPACE_OPEN
// Forward declaration
#ifndef DOXYGEN
template <typename number>
class Vector;
#endif
namespace Functions
{
/**
* This class represents an incremental function. That is, given an arbitrary
* function <code>f</code>, this class will return
* <code>f(t) - f(t - delta_t)</code>, where <code>f(t)</code> denotes the
* function evaluated at time <code>t</code> and, likewise, <code>f(t -
* delta_t)</code> denotes the function evaluated at time <code>t -
* delta_t</code>. The decrement <code>delta_t</code> is set by the method
* set_decrement(). The main application of this class is to transform a given
* Dirichlet boundary condition function into incremental form, as is
* required by some implementations of non-linear solution schemes.
*
* @ingroup functions
*/
template <int dim, typename RangeNumberType = double>
class IncrementalFunction : public Function<dim, RangeNumberType>
{
public:
/**
* Export the value of the template parameter as a static member constant.
* This is sometimes useful in the context of template programming.
*/
static constexpr unsigned int dimension = dim;
/**
* The scalar-valued real type used for representing time.
*/
using time_type = typename Function<dim, RangeNumberType>::time_type;
/**
* Constructor which wraps a given function @p base.
*
* @note This class stores a non-constant reference to @p base
* and will call <code>base.set_time()</code> during evaluation
* in order to evaluate the @p base class at any arbitrary time.
* It is guaranteed that the temporal state of @p base is returned
* to its original settings after each function evaluation in this
* class.
*/
IncrementalFunction(Function<dim, RangeNumberType> &base);
/**
* Return the value of the function at the given point.
*
* Unless there is only one component (i.e. the function is scalar), you
* should state the component you want to have evaluated. By default, the
* value of the first component is computed.
*/
virtual RangeNumberType
value(const Point<dim> &p, const unsigned int component = 0) const override;
/**
* Return all components of a vector-valued function at a given point.
*
* It is required that the @p values vector have the correct size before
* this function is called.
*/
virtual void
vector_value(const Point<dim> &p,
Vector<RangeNumberType> &values) const override;
/**
* Set the time decrement.
*
* It is expected that this value be positive.
*/
void
set_decrement(const time_type delta_t);
private:
/**
* A reference to the function being wrapped.
*/
Function<dim, RangeNumberType> &base;
/**
* The time decrement.
*/
time_type delta_t;
/**
* An auxiliary vector to store values.
*/
mutable Vector<RangeNumberType> values_old;
/**
* Thread mutex for supporting evaluation in multi-threaded contexts.
*/
mutable Threads::Mutex mutex;
};
} // namespace Functions
DEAL_II_NAMESPACE_CLOSE
#endif
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