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// ------------------------------------------------------------------------
//
// SPDX-License-Identifier: LGPL-2.1-or-later
// Copyright (C) 2016 - 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/function_cspline.h>
#include <deal.II/base/point.h>
#ifdef DEAL_II_WITH_GSL
# include <gsl/gsl_spline.h>
# include <algorithm>
# include <cmath>
DEAL_II_NAMESPACE_OPEN
namespace Functions
{
template <int dim>
CSpline<dim>::CSpline(const std::vector<double> &x_,
const std::vector<double> &y_)
: interpolation_points(x_)
, interpolation_values(y_)
, acc(gsl_interp_accel_alloc(),
[](gsl_interp_accel *p) { gsl_interp_accel_free(p); })
, cspline(gsl_spline_alloc(gsl_interp_cspline, interpolation_points.size()),
[](gsl_spline *p) { gsl_spline_free(p); })
{
Assert(interpolation_points.size() > 0,
ExcCSplineEmpty(interpolation_points.size()));
Assert(interpolation_points.size() == interpolation_values.size(),
ExcCSplineSizeMismatch(interpolation_points.size(),
interpolation_values.size()));
// check that input vector @p interpolation_points is provided in ascending order:
for (unsigned int i = 0; i < interpolation_points.size() - 1; ++i)
AssertThrow(interpolation_points[i] < interpolation_points[i + 1],
ExcCSplineOrder(i,
interpolation_points[i],
interpolation_points[i + 1]));
const unsigned int n = interpolation_points.size();
// gsl_spline_init returns something but it seems nobody knows what
gsl_spline_init(cspline.get(),
interpolation_points.data(),
interpolation_values.data(),
n);
}
template <int dim>
double
CSpline<dim>::value(const Point<dim> &p, const unsigned int) const
{
// GSL functions may modify gsl_interp_accel *acc object (last argument).
// This can only work in multithreaded applications if we lock the data
// structures via a mutex.
std::lock_guard<std::mutex> lock(acc_mutex);
const double x = p[0];
Assert(x >= interpolation_points.front() &&
x <= interpolation_points.back(),
ExcCSplineRange(x,
interpolation_points.front(),
interpolation_points.back()));
return gsl_spline_eval(cspline.get(), x, acc.get());
}
template <int dim>
Tensor<1, dim>
CSpline<dim>::gradient(const Point<dim> &p, const unsigned int) const
{
// GSL functions may modify gsl_interp_accel *acc object (last argument).
// This can only work in multithreaded applications if we lock the data
// structures via a mutex.
std::lock_guard<std::mutex> lock(acc_mutex);
const double x = p[0];
Assert(x >= interpolation_points.front() &&
x <= interpolation_points.back(),
ExcCSplineRange(x,
interpolation_points.front(),
interpolation_points.back()));
const double deriv = gsl_spline_eval_deriv(cspline.get(), x, acc.get());
Tensor<1, dim> res;
res[0] = deriv;
return res;
}
template <int dim>
double
CSpline<dim>::laplacian(const Point<dim> &p, const unsigned int) const
{
// GSL functions may modify gsl_interp_accel *acc object (last argument).
// This can only work in multithreaded applications if we lock the data
// structures via a mutex.
std::lock_guard<std::mutex> lock(acc_mutex);
const double x = p[0];
Assert(x >= interpolation_points.front() &&
x <= interpolation_points.back(),
ExcCSplineRange(x,
interpolation_points.front(),
interpolation_points.back()));
return gsl_spline_eval_deriv2(cspline.get(), x, acc.get());
}
template <int dim>
SymmetricTensor<2, dim>
CSpline<dim>::hessian(const Point<dim> &p, const unsigned int) const
{
SymmetricTensor<2, dim> res;
res[0][0] = laplacian(p);
return res;
}
template <int dim>
std::size_t
CSpline<dim>::memory_consumption() const
{
// only simple data elements, so
// use sizeof operator
return sizeof(*this) + 2 * sizeof(double) * interpolation_values.size();
}
// explicit instantiations
template class CSpline<1>;
} // namespace Functions
DEAL_II_NAMESPACE_CLOSE
#endif
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