Added notes concerning the ordering issue when handling sets of LinearFactor::shared_ptrs

cpp/LinearFactor.h

@@ -187,6 +187,9 @@ public:
 
 	/**
 	 * Constructor that combines a set of factors
+	 * NOTE: the combined factor will be depends on a system-dependent
+	 * ordering of the input set of factors.  Do not rely on this order
+	 * when using the function.
 	 * @param factors Set of factors to combine
 	 */
 	CONSTRUCTOR

cpp/LinearFactorGraph.h

@@ -57,12 +57,17 @@ namespace gtsam {
     /**
      * find all the factors that involve the given node and remove them
      * from the factor graph
+     * NOTE: the ordering of the LinearFactor::shared_ptrs will change
+     * between systems, so do not rely on this ordering
      * @param key the key for the given node
      */
     LinearFactorSet find_factors_and_remove(const std::string& key);
 
     /**
      * extract and combine all the factors that involve a given node
+     * NOTE: the combined factor will be depends on a system-dependent
+	 * ordering of the input set of factors.  Do not rely on this order
+	 * when using the function.
      * @param key the key for the given node
      * @return the combined linear factor
      */

cpp/testLinearFactor.cpp

@@ -65,10 +65,9 @@ TEST( LinearFactor, variables )
 
 /* ************************************************************************* */
 
-// NOTE: This test does not pass when running on Linux (Ubuntu 9.04, GCC 4.3.3)
+// NOTE: This test fails due to order dependency in the extraction of factors
-//       systems, and appears to be dependent on the ordering of factors in the 
+//       To fix it, it will be necessary to construct the expected version
-//       set lfg.  Reversing the order in which the matrices are appended will 
+//       of the combined factor taking into account the ordering in the set
-//       make this test work correctly, while the next test will fail.  
 TEST( LinearFactor, linearFactor2 )
 {
   // create a small linear factor graph

cpp/testLinearFactorGraph.cpp

@@ -153,8 +153,10 @@ TEST( LinearFactorGraph, find_separator )
 }
 
 /* ************************************************************************* */
-// Note: This test does not pass when running on Linux(Ubuntu 9.04, GCC 4.3.3) 
+// Note: This test fails on different systems due to a dependency on the ordering
-//       systems.  
+//       of LinearFactor::shared_ptr in STL sets.  Because the ordering is based
+//       on pointer values instead of factor values, the ordering is different
+//       between separate systems.
 TEST( LinearFactorGraph, combine_factors_x1 )
 {	
   // create a small example for a linear factor graph
@@ -163,6 +165,9 @@ TEST( LinearFactorGraph, combine_factors_x1 )
   // combine all factors
   LinearFactor::shared_ptr actual = fg.combine_factors("x1");
 
+  //FIXME: this expected value must be constructed in the order that
+  //       the factors are stored in a set - which differs between systems
+
   // the expected linear factor
   Matrix Al1 = Matrix_(6,2,
 			 0., 0.,
@@ -215,6 +220,9 @@ TEST( LinearFactorGraph, combine_factors_x2 )
   // combine all factors
   LinearFactor::shared_ptr actual = fg.combine_factors("x2");
 
+  // FIXME: change the ordering of the expected to match whatever the real
+  //        ordering is and constructed the expected with the correct order
+
   // the expected linear factor
   Matrix Al1 = Matrix_(4,2,
 			 // l1