The general definitions of the finite element method can today be made so
wide (vide Chapter 3) as to include other useful approximation processes.**
In particular finite difference methods will now be recognized as a subclass
of the procedure** and (with some imagination) the boundary integral method,
which has been lately used with much success for certain classes of problem,
can be brought under the general definition. This generalization is made with
two-fold object. First to improve our understanding - second to incorporate
selective advantages of the alternatives in a unified manner. Chapter 23 is
devoted to a recent development by which the boundary integral and finite
element methodologies are combined.