"The text is supplemented with illustrative exercises that serve to reinforce concepts and methods of treating such problems and to discuss some techniques related to the discretization of equations and treatment, and formulating and solving them. If the book was intended to be used as a text book, its objectives have been largely achieved ... . This is a book that can lend important help to those working in the subject." (Melio Saenz, Research Gate, researchgate.net, June, 2016)