linear_equation.hpp

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/*
 * GHOST (General meta-Heuristic Optimization Solving Tool) is a C++ framework
 * designed to help developers to model and implement optimization problem
 * solving. It contains a meta-heuristic solver aiming to solve any kind of
 * combinatorial and optimization real-time problems represented by a CSP/COP/EF-CSP/EF-COP. 
 *
 * First developed to solve game-related optimization problems, GHOST can be used for
 * any kind of applications where solving combinatorial and optimization problems. In
 * particular, it had been designed to be able to solve not-too-complex problem instances
 * within some milliseconds, making it very suitable for highly reactive or embedded systems.
 * Please visit https://github.com/richoux/GHOST for further information.
 *
 * Copyright (C) 2014-2025 Florian Richoux
 *
 * This file is part of GHOST.
 * GHOST is free software: you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 
 * GHOST is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 
 * You should have received a copy of the GNU General Public License
 * along with GHOST. If not, see http://www.gnu.org/licenses/.
 */
 
#pragma once
 
#include <vector>
 
#include "../variable.hpp"
#include "../constraint.hpp"
 
namespace ghost
{
    namespace global_constraints
    {
        /*
         * Abstract class for Linear Equation constraints
         */
        class LinearEquation : public Constraint
        {
            std::vector<double> _coefficients;
            mutable double _current_sum;
 
        protected:
            double rhs;
    
            /*
             * Constructor with a vector of variable IDs. This vector is internally used by ghost::Constraint
             * to know what variables from the global variable vector it is handling.
             * \param variables_index a const reference to a vector of IDs of variables composing the constraint.
             * \param rhs the right-hand side real number of the equation.
             * \param coefficients the vector of real numbers coefficients for each variable of the equation.
             */
            LinearEquation( const std::vector<int>& variables_index, double rhs, const std::vector<double>& coefficients );
 
            /*
             * Constructor with a vector of variable.
             * \param variables a const reference to a vector of variables composing the constraint.
             * \param rhs the right-hand side real number of the equation.
             * \param coefficients the vector of real numbers coefficients for each variable of the equation.
             */
            LinearEquation( const std::vector<Variable>& variables, double rhs, const std::vector<double>& coefficients );
 
            virtual double compute_error( double sum ) const = 0;
 
            double required_error( const std::vector<Variable*>& variables ) const override;
 
            double optional_delta_error( const std::vector<Variable*>& variables,
                                         const std::vector<int>& variable_indexes,
                                         const std::vector<int>& candidate_values ) const override;
 
            void conditional_update_data_structures( const std::vector<Variable*>& variables, int variable_id, int new_value ) override;
 
        };
    }
}