    // Copyright (C) 2006  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_MATRIx_
    #define DLIB_MATRIx_

    #include "matrix_exp.h"
    #include "matrix_abstract.h"
    #include "../algs.h"
    #include "../serialize.h"
    #include "../enable_if.h"
    #include <sstream>
    #include <algorithm>
    #include "../memory_manager.h"
    #include "../is_kind.h"
    #include "matrix_data_layout.h"
    #include "matrix_assign_fwd.h"
    #include "matrix_op.h"
    #include <utility>
    #ifdef DLIB_HAS_INITIALIZER_LISTS
    #include <initializer_list>
    #endif

    #ifdef MATLAB_MEX_FILE
    #include <mex.h>
    #endif

    #ifdef _MSC_VER
    #pragma warning(push)

    // Disable the following warnings for Visual Studio

    // This warning is:
    //    "warning C4355: 'this' : used in base member initializer list"
    // Which we get from this code but it is not an error so I'm turning this
    // warning off and then turning it back on at the end of the file.
    #pragma warning(disable : 4355)

    // "warning C4723: potential divide by 0" - This warning is triggered in
    // matrix(const std::initializer_list<T>& l) where the compiler can see that
    // matrix<> was templated in a way making NR ending up 0, but division by 0 at runtime
    // is not possible because the division operation is inside "if (NR!=0)" block.
    #pragma warning(disable : 4723)

    // "warning C4724: potential mod by 0" - This warning is triggered in
    // matrix(const std::initializer_list<T>& l) where the compiler can see that
    // matrix<> was templated in a way making NR ending up 0, but mod by 0 at runtime
    // is not possible because the mod operation is inside "if (NR!=0)" block.
    #pragma warning(disable : 4724)

    #endif

    namespace dlib
    {

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

        // This template will perform the needed loop for element multiplication using whichever
        // dimension is provided as a compile time constant (if one is at all).
        template <
            typename LHS,
            typename RHS,
            long lhs_nc = LHS::NC,
            long rhs_nr = RHS::NR
            >
        struct matrix_multiply_helper
        {
            typedef typename LHS::type type;
            template <typename RHS_, typename LHS_>
            inline const static type  eval (
                const RHS_& rhs,
                const LHS_& lhs,
                const long r,
                const long c
            )
            {
                type temp = lhs(r,0)*rhs(0,c);
                for (long i = 1; i < rhs.nr(); ++i)
                {
                    temp += lhs(r,i)*rhs(i,c);
                }
                return temp;
            }
        };

        template <
            typename LHS,
            typename RHS,
            long lhs_nc
            >
        struct matrix_multiply_helper <LHS,RHS,lhs_nc,0>
        {
            typedef typename LHS::type type;
            template <typename RHS_, typename LHS_>
            inline const static type  eval (
                const RHS_& rhs,
                const LHS_& lhs,
                const long r,
                const long c
            )
            {
                type temp = lhs(r,0)*rhs(0,c);
                for (long i = 1; i < lhs.nc(); ++i)
                {
                    temp += lhs(r,i)*rhs(i,c);
                }
                return temp;
            }
        };

        template <typename LHS, typename RHS>
        class matrix_multiply_exp;

        template <typename LHS, typename RHS>
        struct matrix_traits<matrix_multiply_exp<LHS,RHS> >
        {
            typedef typename LHS::type type;
            typedef typename LHS::type const_ret_type;
            typedef typename LHS::mem_manager_type mem_manager_type;
            typedef typename LHS::layout_type layout_type;
            const static long NR = LHS::NR;
            const static long NC = RHS::NC;

    #ifdef DLIB_USE_BLAS
            // if there are BLAS functions to be called then we want to make sure we
            // always evaluate any complex expressions so that the BLAS bindings can happen.
            const static bool lhs_is_costly = (LHS::cost > 2)&&(RHS::NC != 1 || LHS::cost >= 10000);
            const static bool rhs_is_costly = (RHS::cost > 2)&&(LHS::NR != 1 || RHS::cost >= 10000);
    #else
            const static bool lhs_is_costly = (LHS::cost > 4)&&(RHS::NC != 1);
            const static bool rhs_is_costly = (RHS::cost > 4)&&(LHS::NR != 1);
    #endif

            // Note that if we decide that one of the matrices is too costly we will evaluate it
            // into a temporary.  Doing this resets its cost back to 1.
            const static long lhs_cost = ((lhs_is_costly==true)? 1 : (LHS::cost));
            const static long rhs_cost = ((rhs_is_costly==true)? 1 : (RHS::cost));

            // The cost of evaluating an element of a matrix multiply is the cost of evaluating elements from
            // RHS and LHS times the number of rows/columns in the RHS/LHS matrix.  If we don't know the matrix
            // dimensions then just assume it is really large.
            const static long cost = ((tmax<LHS::NC,RHS::NR>::value!=0)? ((lhs_cost+rhs_cost)*tmax<LHS::NC,RHS::NR>::value):(10000));
        };

        template <typename T, bool is_ref> struct conditional_matrix_temp { typedef typename T::matrix_type type; };
        template <typename T> struct conditional_matrix_temp<T,true>      { typedef T& type; };

        template <
            typename LHS,
            typename RHS
            >
        class matrix_multiply_exp : public matrix_exp<matrix_multiply_exp<LHS,RHS> >
        {
            /*!
                REQUIREMENTS ON LHS AND RHS
                    - must be matrix_exp objects.
            !*/
        public:

            typedef typename matrix_traits<matrix_multiply_exp>::type type;
            typedef typename matrix_traits<matrix_multiply_exp>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix_multiply_exp>::mem_manager_type mem_manager_type;
            const static long NR = matrix_traits<matrix_multiply_exp>::NR;
            const static long NC = matrix_traits<matrix_multiply_exp>::NC;
            const static long cost = matrix_traits<matrix_multiply_exp>::cost;
            typedef typename matrix_traits<matrix_multiply_exp>::layout_type layout_type;

            const static bool lhs_is_costly = matrix_traits<matrix_multiply_exp>::lhs_is_costly;
            const static bool rhs_is_costly = matrix_traits<matrix_multiply_exp>::rhs_is_costly;
            const static bool either_is_costly = lhs_is_costly || rhs_is_costly;
            const static bool both_are_costly = lhs_is_costly && rhs_is_costly;

            typedef typename conditional_matrix_temp<const LHS,lhs_is_costly == false>::type LHS_ref_type;
            typedef typename conditional_matrix_temp<const RHS,rhs_is_costly == false>::type RHS_ref_type;

            // This constructor exists simply for the purpose of causing a compile time error if
            // someone tries to create an instance of this object with the wrong kind of objects.
            template <typename T1, typename T2>
            matrix_multiply_exp (T1,T2);

            inline matrix_multiply_exp (
                const LHS& lhs_,
                const RHS& rhs_
            ) :
                lhs(lhs_),
                rhs(rhs_)
            {
                // You are trying to multiply two incompatible matrices together.  The number of columns
                // in the matrix on the left must match the number of rows in the matrix on the right.
                COMPILE_TIME_ASSERT(LHS::NC == RHS::NR || LHS::NC*RHS::NR == 0);
                DLIB_ASSERT(lhs.nc() == rhs.nr() && lhs.size() > 0 && rhs.size() > 0,
                    "\tconst matrix_exp operator*(const matrix_exp& lhs, const matrix_exp& rhs)"
                    << "\n\tYou are trying to multiply two incompatible matrices together"
                    << "\n\tlhs.nr(): " << lhs.nr()
                    << "\n\tlhs.nc(): " << lhs.nc()
                    << "\n\trhs.nr(): " << rhs.nr()
                    << "\n\trhs.nc(): " << rhs.nc()
                    << "\n\t&lhs: " << &lhs
                    << "\n\t&rhs: " << &rhs
                    );

                // You can't multiply matrices together if they don't both contain the same type of elements.
                COMPILE_TIME_ASSERT((is_same_type<typename LHS::type, typename RHS::type>::value == true));
            }

            inline const type operator() (
                const long r,
                const long c
            ) const
            {
                return matrix_multiply_helper<LHS,RHS>::eval(rhs,lhs,r,c);
            }

            inline const type operator() ( long i ) const
            { return matrix_exp<matrix_multiply_exp>::operator()(i); }

            long nr (
            ) const { return lhs.nr(); }

            long nc (
            ) const { return rhs.nc(); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return lhs.aliases(item) || rhs.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return aliases(item); }

            LHS_ref_type lhs;
            RHS_ref_type rhs;
        };

        template < typename EXP1, typename EXP2 >
        inline const matrix_multiply_exp<EXP1, EXP2> operator* (
            const matrix_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        )
        {
            return matrix_multiply_exp<EXP1, EXP2>(m1.ref(), m2.ref());
        }

        template <typename M, bool use_reference = true>
        class matrix_mul_scal_exp;

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

        // Now we declare some overloads that cause any scalar multiplications to percolate
        // up and outside of any matrix multiplies.  Note that we are using the non-reference containing
        // mode of the matrix_mul_scal_exp object since we are passing in locally constructed matrix_multiply_exp
        // objects.  So the matrix_mul_scal_exp object will contain copies of matrix_multiply_exp objects
        // rather than references to them.  This could result in extra matrix copies if the matrix_multiply_exp
        // decided it should evaluate any of its arguments.  So we also try to not apply this percolating operation
        // if the matrix_multiply_exp would contain a fully evaluated copy of the original matrix_mul_scal_exp
        // expression.
        //
        // Also, the reason we want to apply this transformation in the first place is because it (1) makes
        // the expressions going into matrix multiply expressions simpler and (2) it makes it a lot more
        // straightforward to bind BLAS calls to matrix expressions involving scalar multiplies.
        template < typename EXP1, typename EXP2 >
        inline const typename disable_if_c< matrix_multiply_exp<matrix_mul_scal_exp<EXP1>, matrix_mul_scal_exp<EXP2> >::both_are_costly ,
                                            matrix_mul_scal_exp<matrix_multiply_exp<EXP1, EXP2>,false> >::type operator* (
            const matrix_mul_scal_exp<EXP1>& m1,
            const matrix_mul_scal_exp<EXP2>& m2
        )
        {
            typedef matrix_multiply_exp<EXP1, EXP2> exp1;
            typedef matrix_mul_scal_exp<exp1,false> exp2;
            return exp2(exp1(m1.m, m2.m), m1.s*m2.s);
        }

        template < typename EXP1, typename EXP2 >
        inline const typename disable_if_c< matrix_multiply_exp<matrix_mul_scal_exp<EXP1>, EXP2 >::lhs_is_costly ,
                                          matrix_mul_scal_exp<matrix_multiply_exp<EXP1, EXP2>,false> >::type operator* (
            const matrix_mul_scal_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        )
        {
            typedef matrix_multiply_exp<EXP1, EXP2> exp1;
            typedef matrix_mul_scal_exp<exp1,false> exp2;
            return exp2(exp1(m1.m, m2.ref()), m1.s);
        }

        template < typename EXP1, typename EXP2 >
        inline const typename disable_if_c< matrix_multiply_exp<EXP1, matrix_mul_scal_exp<EXP2> >::rhs_is_costly ,
                                          matrix_mul_scal_exp<matrix_multiply_exp<EXP1, EXP2>,false> >::type operator* (
            const matrix_exp<EXP1>& m1,
            const matrix_mul_scal_exp<EXP2>& m2
        )
        {
            typedef matrix_multiply_exp<EXP1, EXP2> exp1;
            typedef matrix_mul_scal_exp<exp1,false> exp2;
            return exp2(exp1(m1.ref(), m2.m), m2.s);
        }

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

        template <typename LHS, typename RHS>
        class matrix_add_exp;

        template <typename LHS, typename RHS>
        struct matrix_traits<matrix_add_exp<LHS,RHS> >
        {
            typedef typename LHS::type type;
            typedef typename LHS::type const_ret_type;
            typedef typename LHS::mem_manager_type mem_manager_type;
            typedef typename LHS::layout_type layout_type;
            const static long NR = (RHS::NR > LHS::NR) ? RHS::NR : LHS::NR;
            const static long NC = (RHS::NC > LHS::NC) ? RHS::NC : LHS::NC;
            const static long cost = LHS::cost+RHS::cost+1;
        };

        template <
            typename LHS,
            typename RHS
            >
        class matrix_add_exp : public matrix_exp<matrix_add_exp<LHS,RHS> >
        {
            /*!
                REQUIREMENTS ON LHS AND RHS
                    - must be matrix_exp objects.
            !*/
        public:
            typedef typename matrix_traits<matrix_add_exp>::type type;
            typedef typename matrix_traits<matrix_add_exp>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix_add_exp>::mem_manager_type mem_manager_type;
            const static long NR = matrix_traits<matrix_add_exp>::NR;
            const static long NC = matrix_traits<matrix_add_exp>::NC;
            const static long cost = matrix_traits<matrix_add_exp>::cost;
            typedef typename matrix_traits<matrix_add_exp>::layout_type layout_type;

            // This constructor exists simply for the purpose of causing a compile time error if
            // someone tries to create an instance of this object with the wrong kind of objects.
            template <typename T1, typename T2>
            matrix_add_exp (T1,T2);

            matrix_add_exp (
                const LHS& lhs_,
                const RHS& rhs_
            ) :
                lhs(lhs_),
                rhs(rhs_)
            {
                // You can only add matrices together if they both have the same number of rows and columns.
                COMPILE_TIME_ASSERT(LHS::NR == RHS::NR || LHS::NR == 0 || RHS::NR == 0);
                COMPILE_TIME_ASSERT(LHS::NC == RHS::NC || LHS::NC == 0 || RHS::NC == 0);
                DLIB_ASSERT(lhs.nc() == rhs.nc() &&
                       lhs.nr() == rhs.nr(),
                    "\tconst matrix_exp operator+(const matrix_exp& lhs, const matrix_exp& rhs)"
                    << "\n\tYou are trying to add two incompatible matrices together"
                    << "\n\tlhs.nr(): " << lhs.nr()
                    << "\n\tlhs.nc(): " << lhs.nc()
                    << "\n\trhs.nr(): " << rhs.nr()
                    << "\n\trhs.nc(): " << rhs.nc()
                    << "\n\t&lhs: " << &lhs
                    << "\n\t&rhs: " << &rhs
                    );

                // You can only add matrices together if they both contain the same types of elements.
                COMPILE_TIME_ASSERT((is_same_type<typename LHS::type, typename RHS::type>::value == true));
            }

            const type operator() (
                long r,
                long c
            ) const { return lhs(r,c) + rhs(r,c); }

            inline const type operator() ( long i ) const
            { return matrix_exp<matrix_add_exp>::operator()(i); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return lhs.aliases(item) || rhs.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return lhs.destructively_aliases(item) || rhs.destructively_aliases(item); }

            long nr (
            ) const { return lhs.nr(); }

            long nc (
            ) const { return lhs.nc(); }

            const LHS& lhs;
            const RHS& rhs;
        };

        template <
            typename EXP1,
            typename EXP2
            >
        inline const matrix_add_exp<EXP1, EXP2> operator+ (
            const matrix_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        )
        {
            return matrix_add_exp<EXP1, EXP2>(m1.ref(),m2.ref());
        }

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

        template <typename LHS, typename RHS>
        class matrix_subtract_exp;

        template <typename LHS, typename RHS>
        struct matrix_traits<matrix_subtract_exp<LHS,RHS> >
        {
            typedef typename LHS::type type;
            typedef typename LHS::type const_ret_type;
            typedef typename LHS::mem_manager_type mem_manager_type;
            typedef typename LHS::layout_type layout_type;
            const static long NR = (RHS::NR > LHS::NR) ? RHS::NR : LHS::NR;
            const static long NC = (RHS::NC > LHS::NC) ? RHS::NC : LHS::NC;
            const static long cost = LHS::cost+RHS::cost+1;
        };

        template <
            typename LHS,
            typename RHS
            >
        class matrix_subtract_exp : public matrix_exp<matrix_subtract_exp<LHS,RHS> >
        {
            /*!
                REQUIREMENTS ON LHS AND RHS
                    - must be matrix_exp objects.
            !*/
        public:
            typedef typename matrix_traits<matrix_subtract_exp>::type type;
            typedef typename matrix_traits<matrix_subtract_exp>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix_subtract_exp>::mem_manager_type mem_manager_type;
            const static long NR = matrix_traits<matrix_subtract_exp>::NR;
            const static long NC = matrix_traits<matrix_subtract_exp>::NC;
            const static long cost = matrix_traits<matrix_subtract_exp>::cost;
            typedef typename matrix_traits<matrix_subtract_exp>::layout_type layout_type;

            // This constructor exists simply for the purpose of causing a compile time error if
            // someone tries to create an instance of this object with the wrong kind of objects.
            template <typename T1, typename T2>
            matrix_subtract_exp (T1,T2);

            matrix_subtract_exp (
                const LHS& lhs_,
                const RHS& rhs_
            ) :
                lhs(lhs_),
                rhs(rhs_)
            {
                // You can only subtract one matrix from another if they both have the same number of rows and columns.
                COMPILE_TIME_ASSERT(LHS::NR == RHS::NR || LHS::NR == 0 || RHS::NR == 0);
                COMPILE_TIME_ASSERT(LHS::NC == RHS::NC || LHS::NC == 0 || RHS::NC == 0);
                DLIB_ASSERT(lhs.nc() == rhs.nc() &&
                       lhs.nr() == rhs.nr(),
                    "\tconst matrix_exp operator-(const matrix_exp& lhs, const matrix_exp& rhs)"
                    << "\n\tYou are trying to subtract two incompatible matrices"
                    << "\n\tlhs.nr(): " << lhs.nr()
                    << "\n\tlhs.nc(): " << lhs.nc()
                    << "\n\trhs.nr(): " << rhs.nr()
                    << "\n\trhs.nc(): " << rhs.nc()
                    << "\n\t&lhs: " << &lhs
                    << "\n\t&rhs: " << &rhs
                    );

                // You can only subtract one matrix from another if they both contain elements of the same type.
                COMPILE_TIME_ASSERT((is_same_type<typename LHS::type, typename RHS::type>::value == true));
            }

            const type operator() (
                long r,
                long c
            ) const { return lhs(r,c) - rhs(r,c); }

            inline const type operator() ( long i ) const
            { return matrix_exp<matrix_subtract_exp>::operator()(i); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return lhs.aliases(item) || rhs.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return lhs.destructively_aliases(item) || rhs.destructively_aliases(item); }

            long nr (
            ) const { return lhs.nr(); }

            long nc (
            ) const { return lhs.nc(); }

            const LHS& lhs;
            const RHS& rhs;
        };

        template <
            typename EXP1,
            typename EXP2
            >
        inline const matrix_subtract_exp<EXP1, EXP2> operator- (
            const matrix_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        )
        {
            return matrix_subtract_exp<EXP1, EXP2>(m1.ref(),m2.ref());
        }

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

        template <typename M>
        class matrix_div_scal_exp;

        template <typename M>
        struct matrix_traits<matrix_div_scal_exp<M> >
        {
            typedef typename M::type type;
            typedef typename M::type const_ret_type;
            typedef typename M::mem_manager_type mem_manager_type;
            typedef typename M::layout_type layout_type;
            const static long NR = M::NR;
            const static long NC = M::NC;
            const static long cost = M::cost+1;
        };

        template <
            typename M
            >
        class matrix_div_scal_exp : public matrix_exp<matrix_div_scal_exp<M> >
        {
            /*!
                REQUIREMENTS ON M
                    - must be a matrix_exp object.
            !*/
        public:
            typedef typename matrix_traits<matrix_div_scal_exp>::type type;
            typedef typename matrix_traits<matrix_div_scal_exp>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix_div_scal_exp>::mem_manager_type mem_manager_type;
            const static long NR = matrix_traits<matrix_div_scal_exp>::NR;
            const static long NC = matrix_traits<matrix_div_scal_exp>::NC;
            const static long cost = matrix_traits<matrix_div_scal_exp>::cost;
            typedef typename matrix_traits<matrix_div_scal_exp>::layout_type layout_type;

            // This constructor exists simply for the purpose of causing a compile time error if
            // someone tries to create an instance of this object with the wrong kind of objects.
            template <typename T1>
            matrix_div_scal_exp (T1, const type&);

            matrix_div_scal_exp (
                const M& m_,
                const type& s_
            ) :
                m(m_),
                s(s_)
            {}

            const type operator() (
                long r,
                long c
            ) const { return m(r,c)/s; }

            inline const type operator() ( long i ) const
            { return matrix_exp<matrix_div_scal_exp>::operator()(i); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return m.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return m.destructively_aliases(item); }

            long nr (
            ) const { return m.nr(); }

            long nc (
            ) const { return m.nc(); }

            const M& m;
            const type s;
        };

        template <
            typename EXP,
            typename S
            >
        inline const typename enable_if_c<std::numeric_limits<typename EXP::type>::is_integer, matrix_div_scal_exp<EXP> >::type operator/ (
            const matrix_exp<EXP>& m,
            const S& s
        )
        {
            return matrix_div_scal_exp<EXP>(m.ref(),static_cast<typename EXP::type>(s));
        }

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

        template <typename M, bool use_reference >
        struct matrix_traits<matrix_mul_scal_exp<M,use_reference> >
        {
            typedef typename M::type type;
            typedef typename M::type const_ret_type;
            typedef typename M::mem_manager_type mem_manager_type;
            typedef typename M::layout_type layout_type;
            const static long NR = M::NR;
            const static long NC = M::NC;
            const static long cost = M::cost+1;
        };

        template <typename T, bool is_ref> struct conditional_reference { typedef T type; };
        template <typename T> struct conditional_reference<T,true>      { typedef T& type; };

        template <
            typename M,
            bool use_reference
            >
        class matrix_mul_scal_exp : public matrix_exp<matrix_mul_scal_exp<M,use_reference> >
        {
            /*!
                REQUIREMENTS ON M
                    - must be a matrix_exp object.

            !*/
        public:
            typedef typename matrix_traits<matrix_mul_scal_exp>::type type;
            typedef typename matrix_traits<matrix_mul_scal_exp>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix_mul_scal_exp>::mem_manager_type mem_manager_type;
            const static long NR = matrix_traits<matrix_mul_scal_exp>::NR;
            const static long NC = matrix_traits<matrix_mul_scal_exp>::NC;
            const static long cost = matrix_traits<matrix_mul_scal_exp>::cost;
            typedef typename matrix_traits<matrix_mul_scal_exp>::layout_type layout_type;

            // You aren't allowed to multiply a matrix of matrices by a scalar.
            COMPILE_TIME_ASSERT(is_matrix<type>::value == false);

            // This constructor exists simply for the purpose of causing a compile time error if
            // someone tries to create an instance of this object with the wrong kind of objects.
            template <typename T1>
            matrix_mul_scal_exp (T1, const type&);

            matrix_mul_scal_exp (
                const M& m_,
                const type& s_
            ) :
                m(m_),
                s(s_)
            {}

            const type operator() (
                long r,
                long c
            ) const { return m(r,c)*s; }

            inline const type operator() ( long i ) const
            { return matrix_exp<matrix_mul_scal_exp>::operator()(i); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return m.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return m.destructively_aliases(item); }

            long nr (
            ) const { return m.nr(); }

            long nc (
            ) const { return m.nc(); }

            typedef typename conditional_reference<const M,use_reference>::type M_ref_type;

            M_ref_type m;
            const type s;
        };

        template <
            typename EXP,
            typename S
            >
        inline typename disable_if<is_matrix<S>, const matrix_mul_scal_exp<EXP> >::type operator* (
            const matrix_exp<EXP>& m,
            const S& s
        )
        {
            typedef typename EXP::type type;
            return matrix_mul_scal_exp<EXP>(m.ref(),static_cast<type>(s));
        }

        template <
            typename EXP,
            typename S,
            bool B
            >
        inline typename disable_if<is_matrix<S>, const matrix_mul_scal_exp<EXP> >::type operator* (
            const matrix_mul_scal_exp<EXP,B>& m,
            const S& s
        )
        {
            typedef typename EXP::type type;
            return matrix_mul_scal_exp<EXP>(m.m,static_cast<type>(s)*m.s);
        }

        template <
            typename EXP,
            typename S
            >
        inline typename disable_if<is_matrix<S>, const matrix_mul_scal_exp<EXP> >::type operator* (
            const S& s,
            const matrix_exp<EXP>& m
        )
        {
            typedef typename EXP::type type;
            return matrix_mul_scal_exp<EXP>(m.ref(),static_cast<type>(s));
        }

        template <
            typename EXP,
            typename S,
            bool B
            >
        inline typename disable_if<is_matrix<S>, const matrix_mul_scal_exp<EXP> >::type operator* (
            const S& s,
            const matrix_mul_scal_exp<EXP,B>& m
        )
        {
            typedef typename EXP::type type;
            return matrix_mul_scal_exp<EXP>(m.m,static_cast<type>(s)*m.s);
        }

        template <
            typename EXP ,
            typename S
            >
        inline const typename disable_if_c<std::numeric_limits<typename EXP::type>::is_integer, matrix_mul_scal_exp<EXP> >::type operator/ (
            const matrix_exp<EXP>& m,
            const S& s
        )
        {
            typedef typename EXP::type type;
            const type one = 1;
            return matrix_mul_scal_exp<EXP>(m.ref(),one/static_cast<type>(s));
        }

        template <
            typename EXP,
            bool B,
            typename S
            >
        inline const typename disable_if_c<std::numeric_limits<typename EXP::type>::is_integer, matrix_mul_scal_exp<EXP> >::type operator/ (
            const matrix_mul_scal_exp<EXP,B>& m,
            const S& s
        )
        {
            typedef typename EXP::type type;
            return matrix_mul_scal_exp<EXP>(m.m,m.s/static_cast<type>(s));
        }

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

        template <typename M>
        struct op_s_div_m : basic_op_m<M>
        {
            typedef typename M::type type;

            op_s_div_m( const M& m_, const type& s_) : basic_op_m<M>(m_), s(s_){}

            const type s;

            const static long cost = M::cost+1;
            typedef const typename M::type const_ret_type;
            const_ret_type apply (long r, long c) const
            {
                return s/this->m(r,c);
            }
        };

        template <
            typename EXP,
            typename S
            >
        const typename disable_if<is_matrix<S>, matrix_op<op_s_div_m<EXP> > >::type operator/ (
            const S& val,
            const matrix_exp<EXP>& m
        )
        {
            typedef typename EXP::type type;

            typedef op_s_div_m<EXP> op;
            return matrix_op<op>(op(m.ref(), static_cast<type>(val)));
        }

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

        template <
            typename EXP
            >
        inline const matrix_mul_scal_exp<EXP> operator- (
            const matrix_exp<EXP>& m
        )
        {
            return matrix_mul_scal_exp<EXP>(m.ref(),-1);
        }

        template <
            typename EXP,
            bool B
            >
        inline const matrix_mul_scal_exp<EXP> operator- (
            const matrix_mul_scal_exp<EXP,B>& m
        )
        {
            return matrix_mul_scal_exp<EXP>(m.m,-1*m.s);
        }

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

        template <typename M>
        struct op_add_scalar : basic_op_m<M>
        {
            typedef typename M::type type;

            op_add_scalar( const M& m_, const type& s_) : basic_op_m<M>(m_), s(s_){}

            const type s;

            const static long cost = M::cost+1;
            typedef const typename M::type const_ret_type;
            const_ret_type apply (long r, long c) const
            {
                return this->m(r,c) + s;
            }
        };

        template <
            typename EXP,
            typename T
            >
        const typename disable_if<is_matrix<T>, matrix_op<op_add_scalar<EXP> > >::type operator+ (
            const matrix_exp<EXP>& m,
            const T& val
        )
        {
            typedef typename EXP::type type;

            typedef op_add_scalar<EXP> op;
            return matrix_op<op>(op(m.ref(), static_cast<type>(val)));
        }

        template <
            typename EXP,
            typename T
            >
        const typename disable_if<is_matrix<T>, matrix_op<op_add_scalar<EXP> > >::type operator+ (
            const T& val,
            const matrix_exp<EXP>& m
        )
        {
            typedef typename EXP::type type;

            typedef op_add_scalar<EXP> op;
            return matrix_op<op>(op(m.ref(), static_cast<type>(val)));
        }

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

        template <typename M>
        struct op_subl_scalar : basic_op_m<M>
        {
            typedef typename M::type type;

            op_subl_scalar( const M& m_, const type& s_) : basic_op_m<M>(m_), s(s_){}

            const type s;

            const static long cost = M::cost+1;
            typedef const typename M::type const_ret_type;
            const_ret_type apply (long r, long c) const
            {
                return s - this->m(r,c) ;
            }
        };

        template <
            typename EXP,
            typename T
            >
        const typename disable_if<is_matrix<T>, matrix_op<op_subl_scalar<EXP> > >::type operator- (
            const T& val,
            const matrix_exp<EXP>& m
        )
        {
            typedef typename EXP::type type;

            typedef op_subl_scalar<EXP> op;
            return matrix_op<op>(op(m.ref(), static_cast<type>(val)));
        }

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

        template <typename M>
        struct op_subr_scalar : basic_op_m<M>
        {
            typedef typename M::type type;

            op_subr_scalar( const M& m_, const type& s_) : basic_op_m<M>(m_), s(s_){}

            const type s;

            const static long cost = M::cost+1;
            typedef const typename M::type const_ret_type;
            const_ret_type apply (long r, long c) const
            {
                return this->m(r,c) - s;
            }
        };

        template <
            typename EXP,
            typename T
            >
        const typename disable_if<is_matrix<T>, matrix_op<op_subr_scalar<EXP> > >::type operator- (
            const matrix_exp<EXP>& m,
            const T& val
        )
        {
            typedef typename EXP::type type;

            typedef op_subr_scalar<EXP> op;
            return matrix_op<op>(op(m.ref(), static_cast<type>(val)));
        }

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

        template <
            typename EXP1,
            typename EXP2
            >
        bool operator== (
            const matrix_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        )
        {
            if (m1.nr() == m2.nr() && m1.nc() == m2.nc())
            {
                for (long r = 0; r < m1.nr(); ++r)
                {
                    for (long c = 0; c < m1.nc(); ++c)
                    {
                        if (m1(r,c) != m2(r,c))
                            return false;
                    }
                }
                return true;
            }
            return false;
        }

        template <
            typename EXP1,
            typename EXP2
            >
        inline bool operator!= (
            const matrix_exp<EXP1>& m1,
            const matrix_exp<EXP2>& m2
        ) { return !(m1 == m2); }

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

        template <typename T>
        struct op_pointer_to_mat;
        template <typename T>
        struct op_pointer_to_col_vect;

        template <
            typename T,
            long num_rows,
            long num_cols,
            typename mem_manager,
            typename layout
            >
        struct matrix_traits<matrix<T,num_rows, num_cols, mem_manager, layout> >
        {
            typedef T type;
            typedef const T& const_ret_type;
            typedef mem_manager mem_manager_type;
            typedef layout layout_type;
            const static long NR = num_rows;
            const static long NC = num_cols;
            const static long cost = 1;

        };

        template <
            typename T,
            long num_rows,
            long num_cols,
            typename mem_manager,
            typename layout
            >
        class matrix : public matrix_exp<matrix<T,num_rows,num_cols, mem_manager,layout> >
        {

            COMPILE_TIME_ASSERT(num_rows >= 0 && num_cols >= 0);

        public:
            typedef typename matrix_traits<matrix>::type type;
            typedef typename matrix_traits<matrix>::const_ret_type const_ret_type;
            typedef typename matrix_traits<matrix>::mem_manager_type mem_manager_type;
            typedef typename matrix_traits<matrix>::layout_type layout_type;
            const static long NR = matrix_traits<matrix>::NR;
            const static long NC = matrix_traits<matrix>::NC;
            const static long cost = matrix_traits<matrix>::cost;
            typedef T*          iterator;
            typedef const T*    const_iterator;

            matrix ()
            {
            }

            explicit matrix (
                long length
            )
            {
                // This object you are trying to call matrix(length) on is not a column or
                // row vector.
                COMPILE_TIME_ASSERT(NR == 1 || NC == 1);
                DLIB_ASSERT( length >= 0,
                    "\tmatrix::matrix(length)"
                    << "\n\tlength must be at least 0"
                    << "\n\tlength: " << length
                    << "\n\tNR:     " << NR
                    << "\n\tNC:     " << NC
                    << "\n\tthis:   " << this
                    );

                if (NR == 1)
                {
                    DLIB_ASSERT(NC == 0 || NC == length,
                        "\tmatrix::matrix(length)"
                        << "\n\tSince this is a statically sized matrix length must equal NC"
                        << "\n\tlength: " << length
                        << "\n\tNR:     " << NR
                        << "\n\tNC:     " << NC
                        << "\n\tthis:   " << this
                        );

                    data.set_size(1,length);
                }
                else
                {
                    DLIB_ASSERT(NR == 0 || NR == length,
                        "\tvoid matrix::set_size(length)"
                        << "\n\tSince this is a statically sized matrix length must equal NR"
                        << "\n\tlength: " << length
                        << "\n\tNR:     " << NR
                        << "\n\tNC:     " << NC
                        << "\n\tthis:   " << this
                        );

                    data.set_size(length,1);
                }
            }

            matrix (
                long rows,
                long cols
            )
            {
                DLIB_ASSERT( (NR == 0 || NR == rows) && ( NC == 0 || NC == cols) &&
                        rows >= 0 && cols >= 0,
                    "\tvoid matrix::matrix(rows, cols)"
                    << "\n\tYou have supplied conflicting matrix dimensions"
                    << "\n\trows: " << rows
                    << "\n\tcols: " << cols
                    << "\n\tNR:   " << NR
                    << "\n\tNC:   " << NC
                    );
                data.set_size(rows,cols);
            }

            template <typename EXP>
            matrix (
                const matrix_exp<EXP>& m
            )
            {
                // You get an error on this line if the matrix m contains a type that isn't
                // the same as the type contained in the target matrix.
                COMPILE_TIME_ASSERT((is_same_type<typename EXP::type,type>::value == true) ||
                                    (is_matrix<typename EXP::type>::value == true));

                // The matrix you are trying to assign m to is a statically sized matrix and
                // m's dimensions don't match that of *this.
                COMPILE_TIME_ASSERT(EXP::NR == NR || NR == 0 || EXP::NR == 0);
                COMPILE_TIME_ASSERT(EXP::NC == NC || NC == 0 || EXP::NC == 0);
                DLIB_ASSERT((NR == 0 || NR == m.nr()) && (NC == 0 || NC == m.nc()),
                    "\tmatrix& matrix::matrix(const matrix_exp& m)"
                    << "\n\tYou are trying to assign a dynamically sized matrix to a statically sized matrix with the wrong size"
                    << "\n\tNR:     " << NR
                    << "\n\tNC:     " << NC
                    << "\n\tm.nr(): " << m.nr()
                    << "\n\tm.nc(): " << m.nc()
                    << "\n\tthis:   " << this
                    );

                data.set_size(m.nr(),m.nc());

                matrix_assign(*this, m);
            }

            matrix (
                const matrix& m
            ) : matrix_exp<matrix>(*this)
            {
                data.set_size(m.nr(),m.nc());
                matrix_assign(*this, m);
            }

    #ifdef DLIB_HAS_INITIALIZER_LISTS
            matrix(const std::initializer_list<T>& l)
            {
                if (NR*NC != 0)
                {
                    DLIB_ASSERT(l.size() == NR*NC,
                        "\t matrix::matrix(const std::initializer_list& l)"
                        << "\n\t You are trying to initialize a statically sized matrix with a list that doesn't have a matching size."
                        << "\n\t l.size(): "<< l.size()
                        << "\n\t NR*NC:    "<< NR*NC);

                    data.set_size(NR, NC);
                }
                else if (NR!=0)
                {
                    DLIB_ASSERT(l.size()%NR == 0,
                        "\t matrix::matrix(const std::initializer_list& l)"
                        << "\n\t You are trying to initialize a statically sized matrix with a list that doesn't have a compatible size."
                        << "\n\t l.size(): "<< l.size()
                        << "\n\t NR:       "<< NR);

                    if (l.size() != 0)
                        data.set_size(NR, l.size()/NR);
                }
                else if (NC!=0)
                {
                    DLIB_ASSERT(l.size()%NC == 0,
                        "\t matrix::matrix(const std::initializer_list& l)"
                        << "\n\t You are trying to initialize a statically sized matrix with a list that doesn't have a compatible size."
                        << "\n\t l.size(): "<< l.size()
                        << "\n\t NC:       "<< NC);

                    if (l.size() != 0)
                        data.set_size(l.size()/NC, NC);
                }
                else if (l.size() != 0)
                {
                    data.set_size(l.size(),1);
                }

                if (l.size() != 0)
                {
                    T* d = &data(0,0);
                    for (auto&& v : l)
                        *d++ = v;
                }

            }

            std::unique_ptr<T[]> steal_memory(
            )
            {
                return data.steal_memory();
            }

            matrix& operator=(const std::initializer_list<T>& l)
            {
                matrix temp(l);
                temp.swap(*this);
                return *this;
            }
    #endif // DLIB_HAS_INITIALIZER_LISTS

    #ifdef DLIB_HAS_RVALUE_REFERENCES
            matrix(matrix&& item)
            {
            #ifdef MATLAB_MEX_FILE
                // You can't move memory around when compiled in a matlab mex file and the
                // different locations have different ownership settings.
                if (data._private_is_owned_by_matlab() == item.data._private_is_owned_by_matlab())
                {
                    swap(item);
                }
                else
                {
                    data.set_size(item.nr(),item.nc());
                    matrix_assign(*this, item);
                }
            #else
                swap(item);
            #endif
            }

            matrix& operator= (
                matrix&& rhs
            )
            {
            #ifdef MATLAB_MEX_FILE
                // You can't move memory around when compiled in a matlab mex file and the
                // different locations have different ownership settings.
                if (data._private_is_owned_by_matlab() == rhs.data._private_is_owned_by_matlab())
                {
                    swap(rhs);
                }
                else
                {
                    data.set_size(rhs.nr(),rhs.nc());
                    matrix_assign(*this, rhs);
                }
            #else
                swap(rhs);
            #endif
                return *this;
            }
    #endif // DLIB_HAS_RVALUE_REFERENCES

            template <typename U, size_t len>
            explicit matrix (
                U (&array)[len]
            )
            {
                COMPILE_TIME_ASSERT(NR*NC == len && len > 0);
                size_t idx = 0;
                for (long r = 0; r < NR; ++r)
                {
                    for (long c = 0; c < NC; ++c)
                    {
                        data(r,c) = static_cast<T>(array[idx]);
                        ++idx;
                    }
                }
            }

            T& operator() (
                long r,
                long c
            )
            {
                DLIB_ASSERT(r < nr() && c < nc() &&
                       r >= 0 && c >= 0,
                    "\tT& matrix::operator(r,c)"
                    << "\n\tYou must give a valid row and column"
                    << "\n\tr:    " << r
                    << "\n\tc:    " << c
                    << "\n\tnr(): " << nr()
                    << "\n\tnc(): " << nc()
                    << "\n\tthis: " << this
                    );
                return data(r,c);
            }

            const T& operator() (
                long r,
                long c
            ) const
            {
                DLIB_ASSERT(r < nr() && c < nc() &&
                       r >= 0 && c >= 0,
                    "\tconst T& matrix::operator(r,c)"
                    << "\n\tYou must give a valid row and column"
                    << "\n\tr:    " << r
                    << "\n\tc:    " << c
                    << "\n\tnr(): " << nr()
                    << "\n\tnc(): " << nc()
                    << "\n\tthis: " << this
                    );
                return data(r,c);
            }

            T& operator() (
                long i
            )
            {
                // You can only use this operator on column vectors.
                COMPILE_TIME_ASSERT(NC == 1 || NC == 0 || NR == 1 || NR == 0);
                DLIB_ASSERT(nc() == 1 || nr() == 1,
                    "\tconst type matrix::operator(i)"
                    << "\n\tYou can only use this operator on column or row vectors"
                    << "\n\ti:    " << i
                    << "\n\tnr(): " << nr()
                    << "\n\tnc(): " << nc()
                    << "\n\tthis: " << this
                    );
                DLIB_ASSERT( 0 <= i && i < size(),
                    "\tconst type matrix::operator(i)"
                    << "\n\tYou must give a valid row/column number"
                    << "\n\ti:      " << i
                    << "\n\tsize(): " << size()
                    << "\n\tthis:   " << this
                    );
                return data(i);
            }

            const T& operator() (
                long i
            ) const
            {
                // You can only use this operator on column vectors.
                COMPILE_TIME_ASSERT(NC == 1 || NC == 0 || NR == 1 || NR == 0);
                DLIB_ASSERT(nc() == 1 || nr() == 1,
                    "\tconst type matrix::operator(i)"
                    << "\n\tYou can only use this operator on column or row vectors"
                    << "\n\ti:    " << i
                    << "\n\tnr(): " << nr()
                    << "\n\tnc(): " << nc()
                    << "\n\tthis: " << this
                    );
                DLIB_ASSERT( 0 <= i && i < size(),
                    "\tconst type matrix::operator(i)"
                    << "\n\tYou must give a valid row/column number"
                    << "\n\ti:      " << i
                    << "\n\tsize(): " << size()
                    << "\n\tthis:   " << this
                    );
                return data(i);
            }

            inline operator const type (
            ) const
            {
                COMPILE_TIME_ASSERT(NC == 1 || NC == 0);
                COMPILE_TIME_ASSERT(NR == 1 || NR == 0);
                DLIB_ASSERT( nr() == 1 && nc() == 1 ,
                    "\tmatrix::operator const type"
                    << "\n\tYou can only attempt to implicit convert a matrix to a scalar if"
                    << "\n\tthe matrix is a 1x1 matrix"
                    << "\n\tnr(): " << nr()
                    << "\n\tnc(): " << nc()
                    << "\n\tthis: " << this
                    );
                return data(0);
            }

    #ifdef MATLAB_MEX_FILE
            void _private_set_mxArray(
                mxArray* mem
            )
            {
                data._private_set_mxArray(mem);
            }

            mxArray* _private_release_mxArray(
            )
            {
                return data._private_release_mxArray();
            }

            void _private_mark_owned_by_matlab()
            {
                data._private_mark_owned_by_matlab();
            }

            bool _private_is_owned_by_matlab()
            {
                return data._private_is_owned_by_matlab();
            }
    #endif

            void set_size (
                long rows,
                long cols
            )
            {
                DLIB_ASSERT( (NR == 0 || NR == rows) && ( NC == 0 || NC == cols) &&
                        rows >= 0 && cols >= 0,
                    "\tvoid matrix::set_size(rows, cols)"
                    << "\n\tYou have supplied conflicting matrix dimensions"
                    << "\n\trows: " << rows
                    << "\n\tcols: " << cols
                    << "\n\tNR:   " << NR
                    << "\n\tNC:   " << NC
                    << "\n\tthis: " << this
                    );
                if (nr() != rows || nc() != cols)
                    data.set_size(rows,cols);
            }

            void set_size (
                long length
            )
            {
                // This object you are trying to call set_size(length) on is not a column or
                // row vector.
                COMPILE_TIME_ASSERT(NR == 1 || NC == 1);
                DLIB_ASSERT( length >= 0,
                    "\tvoid matrix::set_size(length)"
                    << "\n\tlength must be at least 0"
                    << "\n\tlength: " << length
                    << "\n\tNR:     " << NR
                    << "\n\tNC:     " << NC
                    << "\n\tthis:   " << this
                    );

                if (NR == 1)
                {
                    DLIB_ASSERT(NC == 0 || NC == length,
                        "\tvoid matrix::set_size(length)"
                        << "\n\tSince this is a statically sized matrix length must equal NC"
                        << "\n\tlength: " << length
                        << "\n\tNR:     " << NR
                        << "\n\tNC:     " << NC
                        << "\n\tthis:   " << this
                        );

                    if (nc() != length)
                        data.set_size(1,length);
                }
                else
                {
                    DLIB_ASSERT(NR == 0 || NR == length,
                        "\tvoid matrix::set_size(length)"
                        << "\n\tSince this is a statically sized matrix length must equal NR"
                        << "\n\tlength: " << length
                        << "\n\tNR:     " << NR
                        << "\n\tNC:     " << NC
                        << "\n\tthis:   " << this
                        );

                    if (nr() != length)
                        data.set_size(length,1);
                }
            }

            long nr (
            ) const { return data.nr(); }

            long nc (
            ) const { return data.nc(); }

            long size (
            ) const { return data.nr()*data.nc(); }

            template <typename U, size_t len>
            matrix& operator= (
                U (&array)[len]
            )
            {
                COMPILE_TIME_ASSERT(NR*NC == len && len > 0);
                size_t idx = 0;
                for (long r = 0; r < NR; ++r)
                {
                    for (long c = 0; c < NC; ++c)
                    {
                        data(r,c) = static_cast<T>(array[idx]);
                        ++idx;
                    }
                }
                return *this;
            }

            template <typename EXP>
            matrix& operator= (
                const matrix_exp<EXP>& m
            )
            {
                // You get an error on this line if the matrix you are trying to
                // assign m to is a statically sized matrix and  m's dimensions don't
                // match that of *this.
                COMPILE_TIME_ASSERT(EXP::NR == NR || NR == 0 || EXP::NR == 0);
                COMPILE_TIME_ASSERT(EXP::NC == NC || NC == 0 || EXP::NC == 0);
                DLIB_ASSERT((NR == 0 || nr() == m.nr()) &&
                       (NC == 0 || nc() == m.nc()),
                    "\tmatrix& matrix::operator=(const matrix_exp& m)"
                    << "\n\tYou are trying to assign a dynamically sized matrix to a statically sized matrix with the wrong size"
                    << "\n\tnr():   " << nr()
                    << "\n\tnc():   " << nc()
                    << "\n\tm.nr(): " << m.nr()
                    << "\n\tm.nc(): " << m.nc()
                    << "\n\tthis:   " << this
                    );

                // You get an error on this line if the matrix m contains a type that isn't
                // the same as the type contained in the target matrix.
                COMPILE_TIME_ASSERT((is_same_type<typename EXP::type,type>::value == true) ||
                                    (is_matrix<typename EXP::type>::value == true));
                if (m.destructively_aliases(*this) == false)
                {
                    // This if statement is seemingly unnecessary since set_size() contains this
                    // exact same if statement.  However, structuring the code this way causes
                    // gcc to handle the way it inlines this function in a much more favorable way.
                    if (data.nr() == m.nr() && data.nc() == m.nc())
                    {
                        matrix_assign(*this, m);
                    }
                    else
                    {
                        set_size(m.nr(),m.nc());
                        matrix_assign(*this, m);
                    }
                }
                else
                {
                    // we have to use a temporary matrix object here because
                    // *this is aliased inside the matrix_exp m somewhere.
                    matrix temp;
                    temp.set_size(m.nr(),m.nc());
                    matrix_assign(temp, m);
                    temp.swap(*this);
                }
                return *this;
            }

            template <typename EXP>
            matrix& operator += (
                const matrix_exp<EXP>& m
            )
            {
                // The matrix you are trying to assign m to is a statically sized matrix and
                // m's dimensions don't match that of *this.
                COMPILE_TIME_ASSERT(EXP::NR == NR || NR == 0 || EXP::NR == 0);
                COMPILE_TIME_ASSERT(EXP::NC == NC || NC == 0 || EXP::NC == 0);
                COMPILE_TIME_ASSERT((is_same_type<typename EXP::type,type>::value == true));
                if (nr() == m.nr() && nc() == m.nc())
                {
                    if (m.destructively_aliases(*this) == false)
                    {
                        matrix_assign(*this, *this + m);
                    }
                    else
                    {
                        // we have to use a temporary matrix object here because
                        // this->data is aliased inside the matrix_exp m somewhere.
                        matrix temp;
                        temp.set_size(m.nr(),m.nc());
                        matrix_assign(temp, *this + m);
                        temp.swap(*this);
                    }
                }
                else
                {
                    DLIB_ASSERT(size() == 0,
                        "\t const matrix::operator+=(m)"
                        << "\n\t You are trying to add two matrices that have incompatible dimensions.");
                    *this = m;
                }
                return *this;
            }

            template <typename EXP>
            matrix& operator -= (
                const matrix_exp<EXP>& m
            )
            {
                // The matrix you are trying to assign m to is a statically sized matrix and
                // m's dimensions don't match that of *this.
                COMPILE_TIME_ASSERT(EXP::NR == NR || NR == 0 || EXP::NR == 0);
                COMPILE_TIME_ASSERT(EXP::NC == NC || NC == 0 || EXP::NC == 0);
                COMPILE_TIME_ASSERT((is_same_type<typename EXP::type,type>::value == true));
                if (nr() == m.nr() && nc() == m.nc())
                {
                    if (m.destructively_aliases(*this) == false)
                    {
                        matrix_assign(*this, *this - m);
                    }
                    else
                    {
                        // we have to use a temporary matrix object here because
                        // this->data is aliased inside the matrix_exp m somewhere.
                        matrix temp;
                        temp.set_size(m.nr(),m.nc());
                        matrix_assign(temp, *this - m);
                        temp.swap(*this);
                    }
                }
                else
                {
                    DLIB_ASSERT(size() == 0,
                        "\t const matrix::operator-=(m)"
                        << "\n\t You are trying to subtract two matrices that have incompatible dimensions.");
                    *this = -m;
                }
                return *this;
            }

            template <typename EXP>
            matrix& operator *= (
                const matrix_exp<EXP>& m
            )
            {
                *this = *this * m;
                return *this;
            }

            matrix& operator += (
                const matrix& m
            )
            {
                const long size = m.nr()*m.nc();
                if (nr() == m.nr() && nc() == m.nc())
                {
                    for (long i = 0; i < size; ++i)
                        data(i) += m.data(i);
                }
                else
                {
                    DLIB_ASSERT(this->size() == 0,
                        "\t const matrix::operator+=(m)"
                        << "\n\t You are trying to add two matrices that have incompatible dimensions.");

                    set_size(m.nr(), m.nc());
                    for (long i = 0; i < size; ++i)
                        data(i) = m.data(i);
                }
                return *this;
            }

            matrix& operator -= (
                const matrix& m
            )
            {
                const long size = m.nr()*m.nc();
                if (nr() == m.nr() && nc() == m.nc())
                {
                    for (long i = 0; i < size; ++i)
                        data(i) -= m.data(i);
                }
                else
                {
                    DLIB_ASSERT(this->size() == 0,
                        "\t const matrix::operator-=(m)"
                        << "\n\t You are trying to subtract two matrices that have incompatible dimensions.");
                    set_size(m.nr(), m.nc());
                    for (long i = 0; i < size; ++i)
                        data(i) = -m.data(i);
                }
                return *this;
            }

            matrix& operator += (
                const T val
            )
            {
                const size_t size = nr()*(size_t)nc();
                for (size_t i = 0; i < size; ++i)
                    data(i) += val;

                return *this;
            }

            matrix& operator -= (
                const T val
            )
            {
                const size_t size = nr()*(size_t)nc();
                for (size_t i = 0; i < size; ++i)
                    data(i) -= val;

                return *this;
            }

            matrix& operator *= (
                const T a
            )
            {
                *this = *this * a;
                return *this;
            }

            matrix& operator /= (
                const T a
            )
            {
                *this = *this / a;
                return *this;
            }

            matrix& operator= (
                const matrix& m
            )
            {
                if (this != &m)
                {
                    set_size(m.nr(),m.nc());
                    const long size = m.nr()*m.nc();
                    for (long i = 0; i < size; ++i)
                        data(i) = m.data(i);
                }
                return *this;
            }

            void swap (
                matrix& item
            )
            {
                data.swap(item.data);
            }

            template <typename U>
            bool aliases (
                const matrix_exp<U>&
            ) const { return false; }

            bool aliases (
                const matrix_exp<matrix<T,num_rows,num_cols, mem_manager,layout> >& item
            ) const { return (this == &item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>&
            ) const { return false; }

            // These two aliases() routines are defined in matrix_mat.h
            bool aliases (
                const matrix_exp<matrix_op<op_pointer_to_mat<T> > >& item
            ) const;
            bool aliases (
                const matrix_exp<matrix_op<op_pointer_to_col_vect<T> > >& item
            ) const;

            iterator begin()
            {
                if (size() != 0)
                    return &data(0,0);
                else
                    return 0;
            }

            iterator end()
            {
                if (size() != 0)
                    return &data(0,0)+size();
                else
                    return 0;
            }

            const_iterator begin()  const
            {
                if (size() != 0)
                    return &data(0,0);
                else
                    return 0;
            }

            const_iterator end() const
            {
                if (size() != 0)
                    return &data(0,0)+size();
                else
                    return 0;
            }

        private:
            struct literal_assign_helper
            {
                /*
                    This struct is a helper struct returned by the operator<<() function below.  It is
                    used primarily to enable us to put DLIB_CASSERT statements on the usage of the
                    operator<< form of matrix assignment.
                */

                literal_assign_helper(const literal_assign_helper& item) : m(item.m), r(item.r), c(item.c), has_been_used(false) {}
                explicit literal_assign_helper(matrix* m_): m(m_), r(0), c(0),has_been_used(false) {next();}
                ~literal_assign_helper() noexcept(false)
                {
                    DLIB_CASSERT(!has_been_used || r == (*m).nr(),
                                 "You have used the matrix comma based assignment incorrectly by failing to\n"
                                 "supply a full set of values for every element of a matrix object.\n");
                }

                const literal_assign_helper& operator, (
                    const T& val
                ) const
                {
                    DLIB_CASSERT(r < (*m).nr() && c < (*m).nc(),
                                 "You have used the matrix comma based assignment incorrectly by attempting to\n" <<
                                 "supply more values than there are elements in the matrix object being assigned to.\n\n" <<
                                 "Did you forget to call set_size()?"
                                 << "\n\t r: " << r
                                 << "\n\t c: " << c
                                 << "\n\t m->nr(): " << (*m).nr()
                                 << "\n\t m->nc(): " << (*m).nc());
                    (*m)(r,c) = val;
                    next();
                    has_been_used = true;
                    return *this;
                }

            private:

                friend class matrix<T,num_rows,num_cols,mem_manager,layout>;

                void next (
                ) const
                {
                    ++c;
                    if (c == (*m).nc())
                    {
                        c = 0;
                        ++r;
                    }
                }

                matrix* m;
                mutable long r;
                mutable long c;
                mutable bool has_been_used;
            };

        public:

            matrix& operator = (
                const literal_assign_helper& val
            )
            {
                *this = *val.m;
                return *this;
            }

            const literal_assign_helper operator = (
                const T& val
            )
            {
                // assign the given value to every spot in this matrix
                const size_t size = nr()*(size_t)nc();
                for (size_t i = 0; i < size; ++i)
                    data(i) = val;

                // Now return the literal_assign_helper so that the user
                // can use the overloaded comma notation to initialize
                // the matrix if they want to.
                return literal_assign_helper(this);
            }

        private:

            typename layout::template layout<T,NR,NC,mem_manager> data;
        };

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

        template <
            typename T,
            long NR,
            long NC,
            typename mm,
            typename l
            >
        void swap(
            matrix<T,NR,NC,mm,l>& a,
            matrix<T,NR,NC,mm,l>& b
        ) { a.swap(b); }

        template <
            typename T,
            long NR,
            long NC,
            typename mm,
            typename l
            >
        void serialize (
            const matrix<T,NR,NC,mm,l>& item,
            std::ostream& out
        )
        {
            try
            {
                // The reason the serialization is a little funny is because we are trying to
                // maintain backwards compatibility with an older serialization format used by
                // dlib while also encoding things in a way that lets the array2d and matrix
                // objects have compatible serialization formats.
                serialize(-item.nr(),out);
                serialize(-item.nc(),out);
                for (long r = 0; r < item.nr(); ++r)
                {
                    for (long c = 0; c < item.nc(); ++c)
                    {
                        serialize(item(r,c),out);
                    }
                }
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while serializing dlib::matrix");
            }
        }

        template <
            typename T,
            long NR,
            long NC,
            typename mm,
            typename l
            >
        void deserialize (
            matrix<T,NR,NC,mm,l>& item,
            std::istream& in
        )
        {
            try
            {
                long nr, nc;
                deserialize(nr,in);
                deserialize(nc,in);

                // this is the newer serialization format
                if (nr < 0 || nc < 0)
                {
                    nr *= -1;
                    nc *= -1;
                }

                if (NR != 0 && nr != NR)
                    throw serialization_error("Error while deserializing a dlib::matrix.  Invalid rows");
                if (NC != 0 && nc != NC)
                    throw serialization_error("Error while deserializing a dlib::matrix.  Invalid columns");

                item.set_size(nr,nc);
                for (long r = 0; r < nr; ++r)
                {
                    for (long c = 0; c < nc; ++c)
                    {
                        deserialize(item(r,c),in);
                    }
                }
            }
            catch (serialization_error& e)
            {
                throw serialization_error(e.info + "\n   while deserializing a dlib::matrix");
            }
        }

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

        template <
            typename T,
            long NR,
            long NC,
            typename mm,
            typename l
            >
        void serialize (
            const ramdump_t<matrix<T,NR,NC,mm,l>>& item_,
            std::ostream& out
        )
        {
            auto& item = item_.item;
            serialize(item.nr(), out);
            serialize(item.nc(), out);
            if (item.size() != 0)
                out.write((char*)&item(0,0), sizeof(item(0,0))*item.size());
        }

        template <
            typename T,
            long NR,
            long NC,
            typename mm,
            typename l
            >
        void deserialize (
            ramdump_t<matrix<T,NR,NC,mm,l>>&& item_,
            std::istream& in
        )
        {
            auto& item = item_.item;
            long nr, nc;
            deserialize(nr, in);
            deserialize(nc, in);
            item.set_size(nr,nc);
            if (item.size() != 0)
                in.read((char*)&item(0,0), sizeof(item(0,0))*item.size());
        }

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

        template <
            typename EXP
            >
        std::ostream& operator<< (
            std::ostream& out,
            const matrix_exp<EXP>& m
        )
        {
            const std::streamsize old = out.width();

            // first figure out how wide we should make each field
            std::string::size_type w = 0;
            std::ostringstream sout;
            for (long r = 0; r < m.nr(); ++r)
            {
                for (long c = 0; c < m.nc(); ++c)
                {
                    sout << m(r,c);
                    w = std::max(sout.str().size(),w);
                    sout.str("");
                }
            }

            // now actually print it
            for (long r = 0; r < m.nr(); ++r)
            {
                for (long c = 0; c < m.nc(); ++c)
                {
                    out.width(static_cast<std::streamsize>(w));
                    out << m(r,c) << " ";
                }
                out << "\n";
            }
            out.width(old);
            return out;
        }

        /*
        template <
            typename T,
            long NR,
            long NC,
            typename MM,
            typename L
            >
        std::istream& operator>> (
            std::istream& in,
            matrix<T,NR,NC,MM,L>& m
        );

        This function is defined inside the matrix_read_from_istream.h file.
        */

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

        class print_matrix_as_csv_helper
        {
            /*!
                This object is used to define an io manipulator for matrix expressions.
                In particular, this code allows you to write statements like:
                    cout << csv << yourmatrix;
                and have it print the matrix with commas separating each element.
            !*/
        public:
            print_matrix_as_csv_helper (std::ostream& out_) : out(out_) {}

            template <typename EXP>
            std::ostream& operator<< (
                const matrix_exp<EXP>& m
            )
            {
                for (long r = 0; r < m.nr(); ++r)
                {
                    for (long c = 0; c < m.nc(); ++c)
                    {
                        if (c+1 == m.nc())
                            out << m(r,c) << "\n";
                        else
                            out << m(r,c) << ", ";
                    }
                }
                return out;
            }

        private:
            std::ostream& out;
        };

        class print_matrix_as_csv {};
        const print_matrix_as_csv csv = print_matrix_as_csv();
        inline print_matrix_as_csv_helper operator<< (
            std::ostream& out,
            const print_matrix_as_csv&
        )
        {
            return print_matrix_as_csv_helper(out);
        }

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

        template <typename EXP>
        class const_temp_matrix;

        template <
            typename EXP
            >
        struct matrix_traits<const_temp_matrix<EXP> >
        {
            typedef typename EXP::type type;
            typedef typename EXP::const_ret_type const_ret_type;
            typedef typename EXP::mem_manager_type mem_manager_type;
            typedef typename EXP::layout_type layout_type;
            const static long NR = EXP::NR;
            const static long NC = EXP::NC;
            const static long cost = 1;
        };

        template <typename EXP>
        class const_temp_matrix : public matrix_exp<const_temp_matrix<EXP> >, noncopyable
        {
        public:
            typedef typename matrix_traits<const_temp_matrix>::type type;
            typedef typename matrix_traits<const_temp_matrix>::const_ret_type const_ret_type;
            typedef typename matrix_traits<const_temp_matrix>::mem_manager_type mem_manager_type;
            typedef typename matrix_traits<const_temp_matrix>::layout_type layout_type;
            const static long NR = matrix_traits<const_temp_matrix>::NR;
            const static long NC = matrix_traits<const_temp_matrix>::NC;
            const static long cost = matrix_traits<const_temp_matrix>::cost;

            const_temp_matrix (
                const matrix_exp<EXP>& item
            ) :
                ref_(item.ref())
            {}
            const_temp_matrix (
                const EXP& item
            ) :
                ref_(item)
            {}

            const_ret_type operator() (
                long r,
                long c
            ) const { return ref_(r,c); }

            const_ret_type operator() ( long i ) const
            { return ref_(i); }

            template <typename U>
            bool aliases (
                const matrix_exp<U>& item
            ) const { return ref_.aliases(item); }

            template <typename U>
            bool destructively_aliases (
                const matrix_exp<U>& item
            ) const { return ref_.destructively_aliases(item); }

            long nr (
            ) const { return ref_.nr(); }

            long nc (
            ) const { return ref_.nc(); }

        private:

            typename conditional_matrix_temp<const EXP, (EXP::cost <= 1)>::type ref_;
        };

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

        typedef matrix<double,0,0,default_memory_manager,column_major_layout> matrix_colmajor;
        typedef matrix<float,0,0,default_memory_manager,column_major_layout> fmatrix_colmajor;

    }

    #ifdef _MSC_VER
    // restore warnings back to their previous settings
    #pragma warning(pop)
    #endif

    #endif // DLIB_MATRIx_