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/* 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_LINEAR_TRANSFORMATION_H_
#define FUNCTIONS_LINEAR_TRANSFORMATION_H_
#include <cstdlib> // for std::size_t
#include <Eigen/Dense>
namespace Gudhi {
namespace coxeter_triangulation {
/** \class Linear_transformation
* \brief Transforms the zero-set of the function by a given linear transformation.
* The underlying function corresponds to f(M*x), where M is the transformation matrix.
*
* \tparam Function_ The function template parameter. Should be a model of
* the concept FunctionForImplicitManifold.
*/
template <class Function_>
struct Linear_transformation {
/**
* \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 {
Eigen::VectorXd result = fun_(matrix_.householderQr().solve(p));
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 {
Eigen::VectorXd result = fun_.seed();
result = matrix_ * result;
return result;
}
/**
* \brief Constructor of a linearly transformed function.
*
* @param[in] function The function to be linearly transformed.
* @param[in] matrix The transformation matrix. Its dimension should be d*d,
* where d is the domain (ambient) dimension of 'function'.
*/
Linear_transformation(const Function_& function, const Eigen::MatrixXd& matrix) : fun_(function), matrix_(matrix) {}
private:
Function_ fun_;
Eigen::MatrixXd matrix_;
};
/**
* \brief Static constructor of a linearly transformed function.
*
* @param[in] function The function to be linearly transformed.
* @param[in] matrix The transformation matrix. Its dimension should be d*d,
* where d is the domain (ambient) dimension of 'function'.
*
* \tparam Function_ The function template parameter. Should be a model of
* the concept FunctionForImplicitManifold.
*
* \ingroup coxeter_triangulation
*/
template <class Function_>
Linear_transformation<Function_> make_linear_transformation(const Function_& function, const Eigen::MatrixXd& matrix) {
return Linear_transformation<Function_>(function, matrix);
}
} // namespace coxeter_triangulation
} // namespace Gudhi
#endif
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