Dependencies like Plplot and Gnuplot are difficult to support in a single configure script, since these can change at any moment. In particular, Plplot libraries have at times even changed the names of some function calls in a non-backward compatible way. The current configure script includes an option to use Gnuplot as an alternative to Plplot if one becomes desperate. But even Gnuplot has introduced some changes, so one should note which versions of Gnuplot and Plplot exist on the user's system.