MINIMAL SQUARE SPECTRAL FACTORS

Recently there has been renewed interest in the problem of spectral fa ctorization and in particular, the problem of parametrizing all square minimal spectral factors of a given spectrum. For instance, let us me ntion two recent papers in this journal, one of which dealing with mor e computational aspects of this problem (Clements, 1993), the other gi ving a parametrization under additional constraints (Ferrante et al., 1993). This paper is motivated in a large part by (Ferrante et al., 19 93), in fact we shall show that a parametrization similar to the one g iven there can be achieved without one of the additional constraints i mposed in (Ferrante et al., 1993). A secondary aim of this paper is to give an overview of several parametrizations available in the literat ure.