The five contributions describe some key mathematical concepts involved in the study of complex systems and non-perturbative problems. The selection of topics is intended to cross-fertilize the various fields where complex systems theory has made an impact. The book presents specific and detailed results meant for a wide audience of researchers and students. It begins with those contributions which help to set up a general theoretical framework and ends with selected applications to the particular areas of biophysics, statistical physics, astrophysics and cosmology. It also includes an...