d.h

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 * @details
 * This file defines the @ref control_system::derivative::D class, which
 * implements a discrete-time derivative controller.
 *
 * The controller generates a control output based on the rate of change
 * of the control error between a reference value and the measured or
 * current value.
 *
 * The controller maintains the previous control error as internal state
 * and applies a configurable maximum output limit.
 *
 * @tparam T Numeric data type used for the controller calculations.
 *
 * @author Abhinay Kumar
 * @version 1.0.0
 * @date 2026-08-11
 *
 * @copyright
 * Copyright (c) 2026 Abhinay Kumar
 */
 
#ifndef CONTROL_SYSTEM_DERIVATIVE_D_H
#define CONTROL_SYSTEM_DERIVATIVE_D_H
 
#include "../utility/utility.h"
 
namespace control_system
{
 
    namespace derivative
    {

         *
         * @details
         * The D class implements a discrete-time derivative controller
         * using a configurable derivative gain and sampling time.
         *
         * The derivative contribution is calculated from the change in
         * control error between successive controller iterations.
         *
         * The previous control error is maintained as internal state and
         * the controller output is limited by the configured maximum
         * output value.
         *
         * @tparam T Numeric data type used for the controller.
         *
         * @par Example
         * @code{.cpp}
         * control_system::derivative::D<double> controller;
         *
         * controller.init(
         *     0.001,
         *     Kd,
         *     100.0
         * );
         *
         * double output = controller.update(reference, measurement);
         * @endcode
         */
        template <typename T>
        class D
        {
        public:

             * state initialized to their default values.
             */
            D();


             *
             * @param[in] dt_ Controller sampling time in seconds.
             * @param[in] Kd_ Derivative gain.
             * @param[in] u_max_ Maximum allowed controller output.
             *
             * @details
             * Initializes the controller sampling time, derivative gain,
             * and output limit.
             */
            void init(T dt_, T Kd_, T u_max_);

            void set_param(T dt_, T Kd_, T u_max_);

            T update(T x_0, T x);

            void reset();

            void merge(T u_k_1_);

            void set_dt(T dt_);

            void set_Kd(T Kd_);

            void set_u_max(T u_max_);

            T get_dt();

            T get_Kd();

            T get_e_k_1();

            T get_u_max();
 
        private:
            T dt = 0.0;

            T e_k_1 = 0.0;

            T Kd = 0.0;

            bool start = true;

            T u_max = 9999999999;
        };
 
#include "../../src/derivative/d.tpp"
    }
}
 
#endif