    // Copyright (C) 2012  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_KALMAN_FiLTER_ABSTRACT_H__
    #ifdef DLIB_KALMAN_FiLTER_ABSTRACT_H__

    #include "../serialize.h"
    #include "../matrix.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        template <
            long states,
            long measurements
            >
        class kalman_filter
        {
            /*!
                REQUIREMENTS ON states
                    states > 0

                REQUIREMENTS ON measurements
                    measurements > 0

                WHAT THIS OBJECT REPRESENTS
                    This object implements the Kalman filter, which is a tool for
                    recursively estimating the state of a process given measurements
                    related to that process.  To use this tool you will have to
                    be familiar with the workings of the Kalman filter.  An excellent
                    introduction can be found in the paper:
                        An Introduction to the Kalman Filter
                        by Greg Welch and Gary Bishop

            !*/

        public:

            kalman_filter(
            );
            /*!
                - #get_observation_model()    == 0
                - #get_transition_model()     == 0
                - #get_process_noise()        == 0
                - #get_measurement_noise()    == 0
                - #get_current_state()        == 0
                - #get_predicted_next_state() == 0
                - #get_current_estimation_error_covariance() == the identity matrix
            !*/

            void set_observation_model (
                const matrix<double,measurements,states>& H
            );
            /*!
                ensures
                    - #get_observation_model() == H
            !*/

            void set_transition_model  (
                const matrix<double,states,states>& A
            );
            /*!
                ensures
                    - #get_transition_model() == A
            !*/

            void set_process_noise     (
                const matrix<double,states,states>& Q
            );
            /*!
                ensures
                    - #get_process_noise() == Q
            !*/

            void set_measurement_noise (
                const matrix<double,measurements,measurements>& R
            );
            /*!
                ensures
                    - #get_measurement_noise() == R
            !*/

            void set_estimation_error_covariance (
                const matrix<double,states,states>& P
            );
            /*!
                ensures
                    - #get_current_estimation_error_covariance() == P
                      (Note that you should only set this before you start filtering
                      since the Kalman filter will maintain the value of P on its own.
                      So only set this during initialization unless you are sure you
                      understand what you are doing.)
            !*/

            const matrix<double,measurements,states>& get_observation_model (
            ) const;
            /*!
                ensures
                    - Returns the matrix "H" which relates process states x to measurements z.
                      The relation is linear, therefore, z = H*x.  That is, multiplying a
                      state by H gives the measurement you expect to observe for that state.
            !*/

            const matrix<double,states,states>& get_transition_model (
            ) const;
            /*!
                ensures
                    - Returns the matrix "A" which determines how process states change over time.
                      The relation is linear, therefore, given a state vector x, the value you
                      expect it to have at the next time step is A*x.
            !*/

            const matrix<double,states,states>& get_process_noise (
            ) const;
            /*!
                ensures
                    - returns the process noise covariance matrix.  You can think of this
                      covariance matrix as a measure of how wrong the assumption of
                      linear state transitions is.
            !*/

            const matrix<double,measurements,measurements>& get_measurement_noise (
            ) const;
            /*!
                ensures
                    - returns the measurement noise covariance matrix.  That is, when we
                      measure a state x we only obtain H*x corrupted by Gaussian noise.
                      The measurement noise is the covariance matrix of this Gaussian
                      noise which corrupts our measurements.
            !*/

            void update (
            );
            /*!
                ensures
                    - propagates the current state estimate forward in time one
                      time step.  In particular:
                        - #get_current_state() == get_predicted_next_state()
                        - #get_predicted_next_state() == get_transition_model()*get_current_state()
                        - #get_current_estimation_error_covariance() == the propagated value of this covariance matrix
            !*/

            void update (
                const matrix<double,measurements,1>& z
            );
            /*!
                ensures
                    - propagates the current state estimate forward in time one time step.
                      Also applies a correction based on the given measurement z.  In particular:
                        - #get_current_state(), #get_predicted_next_state(), and
                          #get_current_estimation_error_covariance() are updated using the
                          Kalman filter method based on the new measurement in z.
            !*/

            const matrix<double,states,1>& get_current_state(
            ) const;
            /*!
                ensures
                    - returns the current estimate of the state of the process.  This
                      estimate is based on all the measurements supplied to the update()
                      method.
            !*/

            const matrix<double,states,1>& get_predicted_next_state(
            ) const;
            /*!
                ensures
                    - returns the next expected value of the process state.
                    - Specifically, returns get_transition_model()*get_current_state()

            !*/

            const matrix<double,states,states>& get_current_estimation_error_covariance(
            ) const;
            /*!
                ensures
                    - returns the current state error estimation covariance matrix.
                      This matrix captures our uncertainty about the value of get_current_state().
            !*/

        };

    // ----------------------------------------------------------------------------------------

        void serialize (
            const kalman_filter& item,
            std::ostream& out
        );
        /*!
            provides serialization support
        !*/

        void deserialize (
            kalman_filter& item,
            std::istream& in
        );
        /*!
            provides deserialization support
        !*/

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_KALMAN_FiLTER_ABSTRACT_H__