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Diffstat (limited to 'src/Coxeter_triangulation/include/gudhi/Functions/PL_approximation.h')
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diff --git a/src/Coxeter_triangulation/include/gudhi/Functions/PL_approximation.h b/src/Coxeter_triangulation/include/gudhi/Functions/PL_approximation.h new file mode 100644 index 00000000..22071d6d --- /dev/null +++ b/src/Coxeter_triangulation/include/gudhi/Functions/PL_approximation.h @@ -0,0 +1,111 @@ +/* This file is part of the Gudhi Library - https://gudhi.inria.fr/ - which is released under MIT. + * See file LICENSE or go to https://gudhi.inria.fr/licensing/ for full license details. + * Author(s): Siargey Kachanovich + * + * Copyright (C) 2019 Inria + * + * Modification(s): + * - YYYY/MM Author: Description of the modification + */ + +#ifndef FUNCTIONS_PL_APPROXIMATION_H_ +#define FUNCTIONS_PL_APPROXIMATION_H_ + +#include <cstdlib> // for std::size_t + +#include <Eigen/Dense> + +namespace Gudhi { + +namespace coxeter_triangulation { + +/** + * \class PL_approximation + * \brief Constructs a piecewise-linear approximation of a function induced by + * an ambient triangulation. + * + * \tparam Function_ The function template parameter. Should be a model of + * the concept FunctionForImplicitManifold. + * \tparam Triangulation The triangulation template parameter. Should be a model of + * the concept TriangulationForManifoldTracing. + */ +template <class Function_, class Triangulation_> +struct PL_approximation { + /** + * \brief Value of the function at a specified point. + * @param[in] p The input point. The dimension needs to coincide with the ambient dimension. + */ + Eigen::VectorXd operator()(const Eigen::VectorXd& p) const { + std::size_t cod_d = this->cod_d(); + std::size_t amb_d = this->amb_d(); + auto s = tr_.locate_point(p); + Eigen::MatrixXd matrix(cod_d, s.dimension() + 1); + Eigen::MatrixXd vertex_matrix(amb_d + 1, s.dimension() + 1); + for (std::size_t i = 0; i < s.dimension() + 1; ++i) vertex_matrix(0, i) = 1; + std::size_t j = 0; + for (auto v : s.vertex_range()) { + Eigen::VectorXd pt_v = tr_.cartesian_coordinates(v); + Eigen::VectorXd fun_v = fun_(pt_v); + for (std::size_t i = 1; i < amb_d + 1; ++i) vertex_matrix(i, j) = pt_v(i - 1); + for (std::size_t i = 0; i < cod_d; ++i) matrix(i, j) = fun_v(i); + j++; + } + assert(j == s.dimension() + 1); + Eigen::VectorXd z(amb_d + 1); + z(0) = 1; + for (std::size_t i = 1; i < amb_d + 1; ++i) z(i) = p(i - 1); + Eigen::VectorXd lambda = vertex_matrix.colPivHouseholderQr().solve(z); + Eigen::VectorXd result = matrix * lambda; + return result; + } + + /** \brief Returns the domain (ambient) dimension. */ + std::size_t amb_d() const { return fun_.amb_d(); } + + /** \brief Returns the codomain dimension. */ + std::size_t cod_d() const { return fun_.cod_d(); } + + /** \brief Returns a point on the zero-set. */ + Eigen::VectorXd seed() const { + // TODO: not finished. Should use an oracle. + return Eigen::VectorXd(amb_d()); + } + + /** + * \brief Constructor of the piecewise-linear approximation of a function + * induced by an ambient triangulation. + * + * @param[in] function The function. + * @param[in] triangulation The ambient triangulation. + */ + PL_approximation(const Function_& function, const Triangulation_& triangulation) + : fun_(function), tr_(triangulation) {} + + private: + Function_ fun_; + Triangulation_ tr_; +}; + +/** + * \brief Static constructor of the piecewise-linear approximation of a function + * induced by an ambient triangulation. + * + * @param[in] function The function. + * @param[in] triangulation The ambient triangulation. + * + * \tparam Function_ The function template parameter. Should be a model of + * the concept FunctionForImplicitManifold. + * + * \ingroup coxeter_triangulation + */ +template <class Function_, class Triangulation_> +PL_approximation<Function_, Triangulation_> make_pl_approximation(const Function_& function, + const Triangulation_& triangulation) { + return PL_approximation<Function_, Triangulation_>(function, triangulation); +} + +} // namespace coxeter_triangulation + +} // namespace Gudhi + +#endif |