Added the unroll_to_column_vector() function.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403089

dlib/matrix/matrix_utilities.h

@@ -2179,6 +2179,40 @@ namespace dlib
         return exp(a.ref(),b.ref());
     }
 
+// ----------------------------------------------------------------------------------------
+
+    struct op_mat_to_vect 
+    {
+        template <typename EXP>
+        struct op : has_destructive_aliasing
+        {
+            const static long cost = EXP::cost+1;
+            const static long NR = EXP::NC*EXP::NR;
+            const static long NC = 1;
+            typedef typename EXP::type type;
+            typedef typename EXP::mem_manager_type mem_manager_type;
+            template <typename M>
+            static type apply ( const M& m, long r, long c)
+            { return m(r/m.nc(), r%m.nc()); }
+
+            template <typename M>
+            static long nr (const M& m) { return m.size(); }
+            template <typename M>
+            static long nc (const M& m) { return 1; }
+        }; 
+    };
+
+    template <
+        typename EXP
+        >
+    const matrix_unary_exp<EXP,op_mat_to_vect> unroll_to_column_vector (
+        const matrix_exp<EXP>& m
+    )
+    {
+        typedef matrix_unary_exp<EXP,op_mat_to_vect> exp;
+        return exp(m.ref());
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/matrix/matrix_utilities_abstract.h

@@ -348,6 +348,23 @@ namespace dlib
                       R(r, c) == array[r][c]
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    const matrix_exp unroll_to_column_vector (
+        const matrix_exp& m
+    );
+    /*!
+        ensures
+            - returns a matrix M such that: 
+                - is_col_vector(M) == true
+                - M.size() == m.size()
+                - for all valid r and c:
+                    - m(r,c) == M(r*m.nc() + c)
+
+            - i.e. the matrix m is unrolled in row major order into a
+              column vector
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/test/matrix3.cpp

@@ -474,6 +474,30 @@ namespace
             DLIB_TEST(abs((rv4*cv4 + 1.0) - ((rv4*cv4)(0) + 1.0)) < std::sqrt(std::numeric_limits<type>::epsilon())*eps_mul);
 
         }
+
+        {
+            matrix<int> m(2,3), m2(6,1);
+
+            m = 1,2,3,
+                4,5,6;
+
+            m2 = 1,2,3,4,5,6;
+
+            DLIB_TEST(unroll_to_column_vector(m) == m2);
+
+        }
+        {
+            matrix<int,2,3> m(2,3);
+            matrix<int> m2(6,1);
+
+            m = 1,2,3,
+                4,5,6;
+
+            m2 = 1,2,3,4,5,6;
+
+            DLIB_TEST(unroll_to_column_vector(m) == m2);
+
+        }
     }