Added a missing requires clause

dlib/optimization/find_map_nmplp.h

@@ -24,6 +24,13 @@ namespace dlib
         double eps
     )
     {
+        // make sure requires clause is not broken
+        DLIB_ASSERT( eps > 0,
+                     "\t void find_map_nmplp()"
+                     << "\n\t eps must be greater than zero"
+                     << "\n\t eps:  " << eps 
+                );
+
         /*
             This function is an implementation of the NMPLP algorithm introduced in the 
             following paper:

dlib/optimization/find_map_nmplp_abstract.h

@@ -311,6 +311,7 @@ namespace dlib
             - for all valid i: prob.num_states(i) >= 2
             - map_problem == an object with an interface compatible with the map_problem
               object defined at the top of this file.
+            - eps > 0
         ensures
             - This function is a tool for approximately solving the MAP problem in a graphical 
               model or factor graph with pairwise potential functions.  That is, it attempts