Updated find_max_factor_graph_nmplp() to use the version of the algorithm from

the 2011 paper Introduction to dual decomposition for inference by David
Sontag, Amir Globerson, and Tommi Jaakkola since the original 2008 paper had an
error in the algorithm that negatively effected its convergence.  Thanks to
James Gunning for pointing this out.

dlib/optimization/find_max_factor_graph_nmplp_abstract.h

@@ -347,10 +347,13 @@ namespace dlib
               to the MAP problem.  However, for graphs with cycles, the solution may be approximate.
               
 
-            - This function is an implementation of the NMPLP algorithm introduced in the 
-              following paper:
-                Fixing Max-Product: Convergent Message Passing Algorithms for MAP LP-Relaxations 
+            - This function is an implementation of the NMPLP algorithm introduced in the
+              following papers:
+                Fixing Max-Product: Convergent Message Passing Algorithms for MAP LP-Relaxations (2008)
                 by Amir Globerson and Tommi Jaakkola
+
+                Introduction to dual decomposition for inference (2011)
+                by David Sontag, Amir Globerson, and Tommi Jaakkola 
     !*/
 
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