Cross product for vectors of size 2. Fixes #1037

doc/examples/tut_arithmetic_dot_cross.cpp

@@ -9,5 +9,10 @@ int main()
   std::cout << "Dot product: " << v.dot(w) << std::endl;
   double dp = v.adjoint()*w; // automatic conversion of the inner product to a scalar
   std::cout << "Dot product via a matrix product: " << dp << std::endl;
+
   std::cout << "Cross product:\n" << v.cross(w) << std::endl;
+  Eigen::Vector2d v2(1,2);
+  Eigen::Vector2d w2(0,1);
+  double cp = v2.cross(w2); // returning a scalar between size-2 vectors
+  std::cout << "Cross product for 2D vectors: " << cp << std::endl;
 }