text: /*    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_CONSTANT_FUNCTION_H_
  #define FUNCTIONS_CONSTANT_FUNCTION_H_
  
  #include <cstdlib>  // for std::size_t
  
  #include <Eigen/Dense>
  
  namespace Gudhi {
  
  namespace coxeter_triangulation {
  
  /**
   * \class Constant_function
   * \brief A class that encodes a constant function from R^d to R^k.
   * This class does not have any implicit manifold in correspondence.
   */
  struct Constant_function {
    /** \brief Value of the function at a specified point. The value is constant.
     * @param[in] p The input point. The dimension needs to coincide with the ambient dimension.
     */
    Eigen::VectorXd operator()(const Eigen::VectorXd& p) const {
      return value_;
    }
  
    /** \brief Returns the domain dimension. Same as the ambient dimension of the sphere. */
    std::size_t amb_d() const { return d_; };
  
    /** \brief Returns the codomain dimension. Same as the codimension of the sphere. */
    std::size_t cod_d() const { return k_; };
  
    /** \brief No seed point is available. Throws an exception on evocation. */
    Eigen::VectorXd seed() const { throw "Seed invoked on a constant function.\n"; }
  
    Constant_function() {}
  
    /**
     * \brief Constructor of a constant function from R^d to R^m.
     *
     * @param[in] d The domain dimension.
     * @param[in] k The codomain dimension.
     * @param[in] value The constant value of the function.
     */
    Constant_function(std::size_t d, std::size_t k, const Eigen::VectorXd& value) : d_(d), k_(k), value_(value) {}
  
   private:
    std::size_t d_, k_;
    Eigen::VectorXd value_;
  };
  
  }  // namespace coxeter_triangulation
  
  }  // namespace Gudhi
  
  #endif
  