deriv

代码说明：

  This function returns the numerical derivative of an analytic function. Of special note, is the incorporation of the "complex stepderivative"approach which offers greatly improved derivative accuracy compared to approximations. This is especially germain when accuracy at the level of machine precision is a concern. (Programming the finite element toolbox using matlb finite element toolbox, many examples for yourself as there is a very friendly interface, input parameters can be)