Editorial Introduction

Abstract

To explain the background of this part of the book consider

$$ W\left( \lambda \right) = {I_m} - \int\limits_{{ - \infty }}^{\infty } {{e^{{i\lambda t}}}k(t)} dt, - \infty < \lambda < \infty $$

where k is an m × m matrix-valued function of which the entries are in L₁(-∞, ∞) and I stands for the m × m identity matrix.