Made sum() and mean() work with complex numbers.

dlib/matrix/matrix_utilities.h

@@ -1669,13 +1669,26 @@ namespace dlib
     template <
         typename EXP
         >
-    inline const typename matrix_exp<EXP>::type mean (
+    inline const typename disable_if<is_complex<typename EXP::type>, typename matrix_exp<EXP>::type>::type mean (
         const matrix_exp<EXP>& m
     )
     {
         return sum(m)/(m.nr()*m.nc());
     }
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename EXP
+        >
+    inline const typename enable_if<is_complex<typename EXP::type>, typename matrix_exp<EXP>::type>::type mean (
+        const matrix_exp<EXP>& m
+    )
+    {
+        typedef typename EXP::type::value_type type;
+        return sum(m)/(type)(m.nr()*m.nc());
+    }
+
 // ----------------------------------------------------------------------------------------
 
     template <

dlib/test/matrix4.cpp

@@ -775,6 +775,15 @@ namespace
         }
     }
 
+    void test_complex()
+    {
+        matrix<complex<double> > a, b;
+
+        a = complex_matrix(linspace(1,7,7), linspace(2,8,7));
+        b = complex_matrix(linspace(4,10,7), linspace(2,8,7));
+
+        DLIB_TEST(mean(a) == complex<double>(4, 5));
+    }
 
 
     class matrix_tester : public tester
@@ -795,6 +804,8 @@ namespace
             test_stuff();
             for (int i = 0; i < 10; ++i)
                 matrix_test();
+
+            test_complex();
         }
     } a;