PLOTREFINE _ _ _ _ _ _ _ _ _ _ _ _ switch

In general plot tries to generate smooth pictures by evaluating the functions at interior points until the distances are fine enough. This can require a lot of computing time if the single function evaluation is expensive. The refinement is controlled by the switch plotrefine which is on by default. When you turn it off the functions will be evaluated only at the basic points (see plot_xmesh, plot_ymesh).