minor cleanup

dlib/graph_cuts/find_max_factor_graph_potts_abstract.h

@@ -162,7 +162,7 @@ namespace dlib
 
 // ----------------------------------------------------------------------------------------
 
-    struct potts_grid_problem 
+    class potts_grid_problem 
     {
         /*!
             WHAT THIS OBJECT REPRESENTS
@@ -181,6 +181,8 @@ namespace dlib
                 "wraps" around at the borders.  
         !*/
 
+    public:
+
         // This typedef should be for a type like int or double.  It
         // must also be capable of representing signed values.
         typedef an_integer_or_real_type value_type;