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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2021 - 2025 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.
//
// ------------------------------------------------------------------------
#include <deal.II/base/bounding_box.h>
#include <deal.II/base/function_restriction.h>
DEAL_II_NAMESPACE_OPEN
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)
{
AssertIndexRange(component_in_dim_plus_1, dim + 1);
Point<dim + 1> output;
output[component_in_dim_plus_1] = coordinate_value;
for (int d = 0; d < dim; ++d)
{
const unsigned int component_to_write_to =
dealii::internal::coordinate_to_one_dim_higher<dim>(
component_in_dim_plus_1, d);
output[component_to_write_to] = point[d];
}
return output;
}
} // namespace internal
namespace Functions
{
template <int dim>
CoordinateRestriction<dim>::CoordinateRestriction(
const Function<dim + 1> &function,
const unsigned int direction,
const double coordinate_value)
: function(&function)
, restricted_direction(direction)
, coordinate_value(coordinate_value)
{
AssertIndexRange(restricted_direction, dim + 1);
}
template <int dim>
double
CoordinateRestriction<dim>::value(const Point<dim> &point,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point,
restricted_direction,
coordinate_value);
return function->value(full_point, component);
}
template <int dim>
Tensor<1, dim>
CoordinateRestriction<dim>::gradient(const Point<dim> &point,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point,
restricted_direction,
coordinate_value);
const Tensor<1, dim + 1> full_gradient =
function->gradient(full_point, component);
// CoordinateRestriction is constant in restricted direction. Through away
// the derivatives with respect to this direction and copy the other
// values.
Tensor<1, dim> grad;
for (unsigned int d = 0; d < dim; ++d)
{
const unsigned int index_to_write_from =
internal::coordinate_to_one_dim_higher<dim>(restricted_direction, d);
grad[d] = full_gradient[index_to_write_from];
}
return grad;
}
template <int dim>
SymmetricTensor<2, dim>
CoordinateRestriction<dim>::hessian(const Point<dim> &point,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point,
restricted_direction,
coordinate_value);
const Tensor<2, dim + 1> full_hessian =
function->hessian(full_point, component);
// CoordinateRestriction is constant in restricted direction. Through away
// the derivatives with respect to this direction and copy the other
// values.
SymmetricTensor<2, dim> hess;
for (unsigned int i = 0; i < dim; ++i)
{
const unsigned int i_to_write_from =
internal::coordinate_to_one_dim_higher<dim>(restricted_direction, i);
for (unsigned int j = 0; j < dim; ++j)
{
const unsigned int j_to_write_from =
internal::coordinate_to_one_dim_higher<dim>(restricted_direction,
j);
hess[i][j] = full_hessian[i_to_write_from][j_to_write_from];
}
}
return hess;
}
template <int dim>
PointRestriction<dim>::PointRestriction(const Function<dim + 1> &function,
const unsigned int open_direction,
const Point<dim> &point)
: function(&function)
, open_direction(open_direction)
, point(point)
{
AssertIndexRange(open_direction, dim + 1);
}
template <int dim>
double
PointRestriction<dim>::value(const Point<1> &point_1D,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point, open_direction, point_1D[0]);
return function->value(full_point, component);
}
template <int dim>
Tensor<1, 1>
PointRestriction<dim>::gradient(const Point<1> &point_1D,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point, open_direction, point_1D[0]);
const Tensor<1, dim + 1> full_gradient =
function->gradient(full_point, component);
// The PointRestrictions is constant in all but the open direction. Throw
// away the derivatives in all but this direction.
Tensor<1, 1> grad;
grad[0] = full_gradient[open_direction];
return grad;
}
template <int dim>
SymmetricTensor<2, 1>
PointRestriction<dim>::hessian(const Point<1> &point_1D,
const unsigned int component) const
{
const Point<dim + 1> full_point =
internal::create_higher_dim_point(point, open_direction, point_1D[0]);
const Tensor<2, dim + 1> full_hessian =
function->hessian(full_point, component);
// The PointRestrictions is constant in all but the open direction. Throw
// away the derivatives in all but this direction.
SymmetricTensor<2, 1> hess;
hess[0][0] = full_hessian[open_direction][open_direction];
return hess;
}
} // namespace Functions
#include "base/function_restriction.inst"
DEAL_II_NAMESPACE_CLOSE
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