Added an overloaded matrix_assign() that handles symmetric kernel_matrix()

expressions more efficiently by only evaluating the upper triangular part
of the matrix.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403837

dlib/svm/kernel_matrix.h

@@ -183,6 +183,46 @@ namespace dlib
         return matrix_op<op>(op(kern,v,v));
     }
     
+// ----------------------------------------------------------------------------------------
+
+    template <
+        typename matrix_dest_type,
+        typename K,
+        typename V
+        >
+    inline void matrix_assign (
+        matrix_dest_type& dest,
+        const matrix_exp<matrix_op<op_kern_mat<K,V,V> > >& src
+    )
+    /*!
+        Overload matrix assignment so that when a kernel_matrix expression
+        gets assigned it only evaluates half the kernel matrix (since it is symmetric)
+    !*/
+    {
+        // if this is a symmetric kernel matrix
+        if (&src.ref().op.vect1 == &src.ref().op.vect2)
+        {
+            for (long r = 0; r < src.nr(); ++r)
+            {
+                for (long c = r; c < src.nc(); ++c)
+                {
+                    dest(r,c) = dest(c,r) = src(r,c);
+                }
+            }
+        }
+        else
+        {
+            // This isn't a symmetric kernel matrix so just do a normal assignment loop
+            for (long r = 0; r < src.nr(); ++r)
+            {
+                for (long c = 0; c < src.nc(); ++c)
+                {
+                    dest(r,c) = src(r,c);
+                }
+            }
+        }
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }