"An especially intractable breed of problems in physics involves those with very many or an infinite number of degrees of freedom and in addition involve “renormalization.” Renormalization is explained as the existence of very many length or energy scales of importance in the physics of the problem. The renormalization group approach is a way of reducing the complexity of these problems to the point where numerical methods can be used to solve them. The Kondo problem (dilute magnetic alloys) is used as an illustration."