Matrix eigenvalue problems arise in a large number of disciplines of sciences and engineering. They constitute the basic tool used in designing buildings, bridges, and turbines, that are resistent to vibrations. They allow to model queueing networks, and to analyze stability of electrical networks or fluid flow. They also allow the scientist to understand local physical phenonema or to study bifurcation patterns in dynamical systems. In fact the writing of this book was motivated mostly by the second class of problems.