RK4Integrator.hpp

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/* 
 * PURPOSE --- Header file for a class for a 4'th order Runge-Kutta 
 * method for solving a system of  n first order differential equations. 
 * If the initial equation is in the form of n'th order differential equation
 * it must be converted to a system of n first order differential
 * equations.
 *
 */

#ifndef RK4_INTEGRATOR_HPP
#define RK4_INTEGRATOR_HPP

#include <stdlib.h>
#include <vector>

class RK4_SIM
{
    public:
        // Constructor
        // The arguments are self-explanatory
        // If you specify initial conditions, the parameter _initial_state 
        // should point to a vector of size _plant_order, so that correct 
        // initialization could be performed.
        RK4_SIM(int _plant_order,
                int _ctrl_order,
                double _integration_step = 0.0001, 
                double _initial_time = 0.0, 
                double *_initial_state = NULL);  

        // Destructor
        virtual ~RK4_SIM();

        // Initilaizes simulation parameters
        void init_param(double _integration_step, 
                double _initial_time, 
                double *_initial_state);  

        void solve (void); // Performs one step simulation

        // DERIV contains the dynamic equations of the system in the 
        // form: xdot = f(t,x,u); arguments are the time t, present state 
        // values x, the present control value u, and values of the derivatives 
        // of the states xdot (calculated inside of the funtcion). 
        // It is overloaded in the derived class!!!
        virtual void DERIV(const double t, const double *x, 
                const double *u, double *xdot) {};

    protected:
        int plant_order; // Num of plant states
        int ctrl_order; // Num of control inputs
        double integration_step; // Integration step size

    public:

        std::vector<double> plant_state; // Current System states
        std::vector<double> ctrl_input; // Current Controller output

        double current_time;  // Current time
        int rk4_sim_err;   // Variable to hold an error number

    private:
        std::vector<double> f1; 
        std::vector<double> f2; 
        std::vector<double> f3; 
        std::vector<double> f4; 
        std::vector<double> temp; // Runge-Kutta Coefficients

        // Functions which calculate RK coefficients
        inline void F1 (void); 
        inline void F2 (void);
        inline void F3 (void);
        inline void F4 (void);
};
#endif