function_restriction.h

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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2021 - 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_function_restriction_h
#define dealii_function_restriction_h
 
#include <deal.II/base/function.h>
#include <deal.II/base/observer_pointer.h>
#include <deal.II/base/point.h>
#include <deal.II/base/tensor.h>
 
DEAL_II_NAMESPACE_OPEN
 
namespace Functions
{
  template <int dim>
  class CoordinateRestriction : public Function<dim>
  {
  public:
    CoordinateRestriction(const Function<dim + 1> &function,
                          const unsigned int       direction,
                          const double             coordinate_value);
 
    double
    value(const Point<dim> &point, const unsigned int component) const override;
 
    Tensor<1, dim>
    gradient(const Point<dim>  &point,
             const unsigned int component) const override;
 
    SymmetricTensor<2, dim>
    hessian(const Point<dim>  &point,
            const unsigned int component) const override;
 
  private:
    // The higher-dimensional function that has been restricted.
    const ObserverPointer<const Function<dim + 1>> function;
 
    // The (`dim + 1`)-coordinate direction that has been restricted.
    const unsigned int restricted_direction;
 
    // Value of the restricted coordinate.
    const double coordinate_value;
  };
 
 
 
  template <int dim>
  class PointRestriction : public Function<1>
  {
  public:
    PointRestriction(const Function<dim + 1> &function,
                     const unsigned int       open_direction,
                     const Point<dim>        &point);
 
    double
    value(const Point<1> &point, const unsigned int component) const override;
 
    Tensor<1, 1>
    gradient(const Point<1>    &point,
             const unsigned int component) const override;
 
    SymmetricTensor<2, 1>
    hessian(const Point<1> &point, const unsigned int component) const override;
 
  private:
    // The higher-dimensional function that has been restricted.
    const ObserverPointer<const Function<dim + 1>> function;
 
    // The (`dim + 1`)-coordinate direction that is kept "open"
    const unsigned int open_direction;
 
    // The point that we have restricted the above function to.
    const Point<dim> point;
  };
 
} // namespace Functions
 
 
namespace internal
{
  template <int dim>
  Point<dim + 1>
  create_higher_dim_point(const Point<dim>  &point,
                          const unsigned int component_in_dim_plus_1,
                          const double       coordinate_value);
} // namespace internal
 
DEAL_II_NAMESPACE_CLOSE
 
#endif /* dealii_function_restriction_h */