[involves] checks whether variable with that key is involved in any factor

cpp/FactorGraph.h

@@ -92,6 +92,11 @@ namespace gtsam {
 		/** return keys in some random order */
 		Ordering keys() const;
 
+		/** Check whether a factor with this variable exists */
+		bool involves(const std::string& key) {
+			return !(indices_.find(key)==indices_.end());
+		}
+
 		/**
 		 * Compute colamd ordering
 		 */

cpp/testGaussianFactorGraph.cpp

@@ -527,6 +527,16 @@ TEST( GaussianFactorGraph, keys )
   CHECK(assert_equal(expected,fg.keys()));
 }
 
+/* ************************************************************************* */
+TEST( GaussianFactorGraph, involves )
+{
+  GaussianFactorGraph fg = createGaussianFactorGraph();
+  CHECK(fg.involves("l1"));
+  CHECK(fg.involves("x1"));
+  CHECK(fg.involves("x2"));
+  CHECK(!fg.involves("x3"));
+}
+
 /* ************************************************************************* */
 // Tests ported from ConstrainedGaussianFactorGraph
 /* ************************************************************************* */