    // Copyright (C) 2009  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_SVm_KERNEL_MATRIX_ABSTRACT_
    #ifdef DLIB_SVm_KERNEL_MATRIX_ABSTRACT_

    #include <vector>
    #include "kernel_abstract.h"
    #include "../matrix/matrix_abstract.h"
    #include "../algs.h"

    namespace dlib
    {

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

        template <
            typename kernel_type,
            typename V
            >
        const matrix_exp kernel_matrix (
            const kernel_type& kernel,
            const V& v
        );
        /*!
            requires
                - kernel == a kernel function object as defined by the file dlib/svm/kernel_abstract.h.
                  This kernel must also be capable of operating on the contents of v.
                - V == dlib::matrix, std::vector, dlib::std_vector_c, dlib::random_subset_selector,
                  dlib::linearly_independent_subset_finder, or kernel_type::sample_type.
                - if (V is a dlib::matrix) then
                    - is_vector(v) == true
            ensures
                - if (V is of type kernel_type::sample_type) then
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R.size() == 1
                        - R(0,0) == kernel(v,v)
                - else
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R is a square matrix of v.size() rows by v.size() columns
                        - for all valid r and c:
                            - R(r,c) == kernel(v(r), v(c))
        !*/

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

        template <
            typename kernel_type,
            typename V1,
            typename V2
            >
        const matrix_exp kernel_matrix (
            const kernel_type& kernel,
            const V1& v1,
            const V2& v2
        );
        /*!
            requires
                - kernel == a kernel function object as defined by the file dlib/svm/kernel_abstract.h
                  This kernel must also be capable of operating on the contents of v1 and v2.
                - V1 == dlib::matrix, std::vector, dlib::std_vector_c, dlib::random_subset_selector,
                  dlib::linearly_independent_subset_finder, or kernel_type::sample_type.
                - V2 == dlib::matrix, std::vector, dlib::std_vector_c, dlib::random_subset_selector,
                  dlib::linearly_independent_subset_finder, or kernel_type::sample_type.
                - if (V1 is a dlib::matrix) then
                    - is_vector(v1) == true
                - if (V2 is a dlib::matrix) then
                    - is_vector(v2) == true
            ensures
                - if (V1 and V2 are of type kernel_type::sample_type) then
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R.size() == 1
                        - R(0,0) == kernel(v1,v2)
                - else if (V1 is of type kernel_type::sample_type) then
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R.nr() == 1
                        - R.nc() == v2.size()
                        - for all valid c:
                            - R(0,c) == kernel(v1, v2(c))
                - else if (V2 is of type kernel_type::sample_type) then
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R.nr() == v1.size()
                        - R.nc() == 1
                        - for all valid r:
                            - R(r,0) == kernel(v1(r), v2)
                - else
                    - returns a matrix R such that:
                        - R::type == kernel_type::scalar_type
                        - R.nr() == v1.size()
                        - R.nc() == v2.size()
                        - for all valid r and c:
                            - R(r,c) == kernel(v1(r), v2(c))

                A note about aliasing (see the examples/matrix_expressions_ex.cpp example program
                for a discussion of what aliasing is in the context of the dlib::matrix):
                    kernel_matrix() expressions can detect aliasing of an argument if that
                    argument is of type kernel_type::sample_type.  However, it can't detect
                    aliasing though std::vectors or other "list of sample type" container class
                    arguments.  This means that it is safe to assign a kernel_matrix() expression
                    to a sample_type if V1 or V2 are of sample_type but not safe otherwise.  However,
                    since the latter case results in a general n by m matrix rather than a column
                    or row vector you shouldn't ever be doing it anyway.
        !*/

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

    }

    #endif // DLIB_SVm_KERNEL_MATRIX_ABSTRACT_