Q()

Copy the function in Appendix A into the file ``Q.m''. It evaluates an operator which is needed for the expression for the gradient in the general case of non-constant $\vec f$. Note that the subscript ``$U$'' to the operator ``$Q_U(X)$'' is sent as the second argument to the function. (Type ``help Q'' at the octave prompt after installing the file ``Q.m'' into your working directory.)