Provided (some) printing functionality

gtsam/nonlinear/Expression-inl.h

@@ -34,6 +34,7 @@
 #include <boost/mpl/fold.hpp>
 namespace MPL = boost::mpl::placeholders;
 
+#include <typeinfo>       // operator typeid
 #include <map>
 
 class ExpressionFactorBinaryTest;
@@ -247,6 +248,13 @@ public:
   virtual ~ExpressionNode() {
   }
 
+  /// Streaming
+  GTSAM_EXPORT friend std::ostream &operator<<(std::ostream &os,
+      const ExpressionNode& node) {
+    os << "Expression of type " << typeid(int).name() << std::endl;
+    if (node.traceSize_>0) os << node.traceSize_ << std::endl;
+  }
+
   /// Return keys that play in this expression as a set
   virtual std::set<Key> keys() const {
     std::set<Key> keys;

gtsam/nonlinear/Expression.h

@@ -52,6 +52,11 @@ private:
 
 public:
 
+  /// Print
+  void print(const std::string& s) const {
+    std::cout << s << root_ << std::endl;
+  }
+
   // Construct a constant expression
   Expression(const T& value) :
       root_(new ConstantExpression<T>(value)) {