http://web.eecs.umich.edu/~fessler/course/451/l/pdf/c3.pdf
http://math.fullerton.edu/mathews/c2003/ZTransformIntroMod.html
http://dea.brunel.ac.uk/cmsp/Home_Saeed_Vaseghi/Chapter04-Z-Transform.pdf
http://books.google.com/books?id=uHs7gpNKqTEC&source=gbs_similarbooks
http://books.google.com/books/about/An_introduction_to_the_Laplace_transform.html?id=UU7vAAAAMAAJ