Removed a bug in the sum() and variance() functions that

caused them to seg fault when they were used on certain
matrix of matrix objects.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%402405

dlib/matrix/matrix_utilities.h

@@ -2813,7 +2813,10 @@ namespace dlib
         typedef typename matrix_exp<EXP>::type type;
 
         type val;
+        if (m.size() > 0)
+            val.set_size(m(0,0).nr(),m(0,0).nc()); 
         set_all_elements(val,0);
+
         for (long r = 0; r < m.nr(); ++r)
         {
             for (long c = 0; c < m.nc(); ++c)
@@ -2876,6 +2879,9 @@ namespace dlib
         typedef typename matrix_exp<EXP>::type type;
 
         type val;
+        if (m.size() > 0)
+            val.set_size(m(0,0).nr(), m(0,0).nc());
+
         set_all_elements(val,0);
         for (long r = 0; r < m.nr(); ++r)
         {
@@ -2885,7 +2891,7 @@ namespace dlib
             }
         }
 
-        if (m.nr() * m.nc() == 1)
+        if (m.nr() * m.nc() <= 1)
             return val;
         else
             return val/(m.nr()*m.nc() - 1);

dlib/test/matrix.cpp

@@ -807,6 +807,14 @@ namespace
             m(0,0) = uniform_matrix<double,3,1>(9);
             DLIB_CASSERT((round_zeros(variance(m)) == uniform_matrix<double,3,1>(16)),"");
             DLIB_CASSERT((round_zeros(mean(m)) == uniform_matrix<double,3,1>(3)),"");
+
+            matrix<matrix<double> > m2(2,2);
+            set_all_elements(m2,uniform_matrix<double,3,1>(1));
+            DLIB_CASSERT((round_zeros(variance(m2)) == uniform_matrix<double,3,1>(0)),"");
+            DLIB_CASSERT((round_zeros(mean(m2)) == uniform_matrix<double,3,1>(1)),"");
+            m2(0,0) = uniform_matrix<double,3,1>(9);
+            DLIB_CASSERT((round_zeros(variance(m2)) == uniform_matrix<double,3,1>(16)),"");
+            DLIB_CASSERT((round_zeros(mean(m2)) == uniform_matrix<double,3,1>(3)),"");
         }
 
         {