Added MakeJacobian meta-function

gtsam/base/OptionalJacobian.h

@@ -171,6 +171,16 @@ public:
 // forward declare
 template <typename T> struct traits;
 
+/**
+ * @brief: meta-function to generate Jacobian
+ * @param T return type
+ * @param A argument type
+ */
+template <class T, class A>
+struct MakeJacobian {
+  typedef Eigen::Matrix<double, traits<T>::dimension, traits<A>::dimension> type;
+};
+
 /**
  * @brief: meta-function to generate JacobianTA optional reference
  * Used mainly by Expressions