Abstract. Given an arbitrary complex-valued infinite matrix A = (a ij ), i = 1, . . . , ∞; j = 1, . . . , ∞ and a positive integer n we introduce a naturally associated polynomial basis B A of C[x 0 , . . . , xn]. We discuss some properties of the locus of common zeros of all polynomials in B A having a given degree m; the latter locus can be interpreted as the spectrum of the m × (m + n)-submatrix of A formed by its m first rows and (m + n) first columns. We initiate the study of the asymptotics of these spectra when m → ∞ in the case when A is a banded Toeplitz matrix. In particular, we present and partially prove a conjectural multivariate analog of the well-known Schmidt-Spitzer theorem which describes the spectral asymptotics for the sequence of principal minors of an arbitrary banded Toeplitz matrix. Finally, we discuss relations between polynomial bases B A and multivariate orthogonal polynomials.
IntroductionThe approach of this paper is motivated by the modern interpretation of the Heine-Stieltjes multiparameter spectral problem as presented in [9] and [10]. Let us recall some relevant results in the matrix set-up.Given integers m > 0 and n ≥ 0 consider the space M at(m, m + n) of complexvalued m × (m + n)-matrices. For s = 0, . . . , n define the s-th unit matrix(In what follows the sizes of matrices can be infinite.)Definition 1 (see [10]). Given a matrix A ∈ M at(m, m + n) define its eigenvalue locus E A asFor n = 0, E A coincides with the usual set of eigenvalues of a square matrix A. eigenvalue tuples (x 0 , x 1 , . . . , x n ) such that A − n s=0 x s I s has rank smaller than m. Remark 3. Notice that for n > 0, the locus E A is not a complete intersection since it is given by the vanishing of all maximal minors of A. (A similar phenomenon can be observed for common zeros of multivariate Schur polynomials, since Schur polynomials are given by determinant formulas.)2000 Mathematics Subject Classification. Primary 15B07; Secondary 34L20, 35P20.