Made keys_ protected to allow initialization in a constructor body, added constructor for NonlinearFactor allowing more than two keys

gtsam/inference/Factor.h

@@ -70,7 +70,8 @@ public:
   /** Const iterator over keys */
   typedef typename std::vector<Key>::const_iterator const_iterator;
 
-private:
+//private: // FIXME: factors that manually initialize keys_ break in this case
+protected:
 
   // The keys involved in this factor
   std::vector<Key> keys_;

gtsam/nonlinear/NonlinearFactor.h

@@ -99,6 +99,14 @@ namespace gtsam {
 			Factor<Symbol>(j1,j2), noiseModel_(noiseModel) {
 		}
 
+		/**
+		 * Constructor - arbitrary number of keys
+		 * @param keys is the set of Symbols in the factor
+		 */
+		NonlinearFactor(const SharedGaussian& noiseModel, const std::set<Symbol>& keys) :
+			Factor<Symbol>(keys), noiseModel_(noiseModel) {
+		}
+
 		/** print */
 		virtual void print(const std::string& s = "") const {
 			std::cout << s << ": NonlinearFactor\n";