Clarified spec and added more tests.

dlib/graph_cuts/min_cut_abstract.h

@@ -429,7 +429,7 @@ namespace dlib
                     - #g.get_flow(i,j) == the residual flow capacity left after the max 
                       possible amount of flow is passing from the source node to the sink
                       node.  For example, this means that #g.get_flow(i,j) == 0 whenever 
-                      node i and j are in different cuts.  
+                      node i is in the SOURCE_CUT and j is in the SINK_CUT. 
                     - #g.get_flow(i,j) >= 0
         !*/
 

dlib/test/graph_cuts.cpp

@@ -756,6 +756,20 @@ namespace
 
         print_graph(g1);
 
+        // make sure the flow residuals are 0 at the cut locations
+        for (unsigned long i = 0; i < g1.number_of_nodes(); ++i)
+        {
+            for (unsigned long j = 0; j < g1.node(i).number_of_children(); ++j)
+            {
+                if ((g1.node(i).data == SOURCE_CUT && g1.node(i).child(j).data != SOURCE_CUT) ||
+                    (g1.node(i).data != SINK_CUT && g1.node(i).child(j).data == SINK_CUT)
+                    )
+                {
+                    DLIB_TEST_MSG(g1.node(i).child_edge(j) == 0, g1.node(i).child_edge(j));
+                }
+            }
+        }
+
         // copy the edge weights from g2 back to g1 so we can compute cut scores
         copy_edge_weights(g1, g2);