© 1990 by Institute of Mathematics and its Applications
A Simple Geometrical Proof of the Box Theorem
School of Electrical and Electronic Engineering, Nanyang Technological Institute Nanyang Avenue, Singapore 2263
Chapellat and Bhattacfaaryya (1989) derived a generalization of Kharitonovs theorem for real interval polynomials called the box theorem. The box theorem states that a family of polynomials F(s) = Q1(s)P1(s) +...+ Qm(s)Pm(s), where Q1(s) are fixed real polynomials and P1(s) are real interval polynomials, is Hurwitz if and only if a prescribed set of m x 4m line segments is Hurwitz. Moreover, for special classes of real polynomials Q1(s) (odd or even polynomials), this set collapses to a discrete set of polynomials. In this paper, a simple geometrical proof of the box theorem is presented, and the theorem is also generalized so as to be applicable to complex polynomi