Added a tensor_product() function for the matrix object.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402570

dlib/matrix/matrix_utilities.h

@@ -3835,6 +3835,46 @@ namespace dlib
 
     }
 
+// ----------------------------------------------------------------------------------------
+
+    struct op_tensor_product
+    {
+        template <typename EXP1, typename EXP2>
+        struct op : public has_destructive_aliasing
+        {
+            const static long NR = EXP1::NR*EXP2::NR;
+            const static long NC = EXP1::NC*EXP2::NC;
+            typedef typename EXP1::type type;
+            typedef typename EXP1::mem_manager_type mem_manager_type;
+
+            template <typename M1, typename M2>
+            static type apply ( const M1& m1, const M2& m2 , long r, long c)
+            { 
+                return m1(r/m2.nr(),c/m2.nc())*m2(r%m2.nr(),c%m2.nc()); 
+            }
+
+
+            template <typename M1, typename M2>
+            static long nr (const M1& m1, const M2& m2 ) { return m1.nr()*m2.nr(); }
+            template <typename M1, typename M2>
+            static long nc (const M1& m1, const M2& m2 ) { return m1.nc()*m2.nc(); }
+        };
+    };
+
+    template <
+        typename EXP1,
+        typename EXP2
+        >
+    inline const matrix_exp<matrix_binary_exp<EXP1,EXP2,op_tensor_product> > tensor_product (
+        const matrix_exp<EXP1>& a,
+        const matrix_exp<EXP2>& b 
+    )
+    {
+        COMPILE_TIME_ASSERT((is_same_type<typename EXP1::type,typename EXP2::type>::value == true));
+        typedef matrix_binary_exp<EXP1,EXP2,op_tensor_product> exp;
+        return matrix_exp<exp>(exp(a.ref(),b.ref()));
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/matrix/matrix_utilities_abstract.h

@@ -574,6 +574,25 @@ namespace dlib
         performs pointwise_multiply(pointwise_multiply(a,b),pointwise_multiply(c,d));
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    const matrix_exp tensor_product (
+        const matrix_exp& a,
+        const matrix_exp& b 
+    );
+    /*!
+        requires
+            - a and b both contain the same type of element
+        ensures
+            - returns a matrix R such that:
+                - R::type == the same type that was in a and b.
+                - R.nr() == a.nr()*b.nr()  
+                - R.nc() == a.nc()*b.nc()  
+                - for all valid r and c:
+                  R(r,c) == a(r/b.nr(), c/b.nc()) * b(r%b.nr(), c%b.nc())
+                - I.e. R is the tensor product of matrix a with matrix b
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     const matrix_exp scale_columns (