3,627 research outputs found
Around multivariate Schmidt-Spitzer theorem
Given an arbitrary complex-valued infinite matrix A and a positive integer n
we introduce a naturally associated polynomial basis B_A of C[x0...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 goes to infinity
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
Recent progress on truncated Toeplitz operators
This paper is a survey on the emerging theory of truncated Toeplitz
operators. We begin with a brief introduction to the subject and then highlight
the many recent developments in the field since Sarason's seminal paper in
2007.Comment: 46 page
General soliton matrices in the Riemann-Hilbert problem for integrable nonlinear equations
We derive the soliton matrices corresponding to an arbitrary number of
higher-order normal zeros for the matrix Riemann-Hilbert problem of arbitrary
matrix dimension, thus giving the complete solution to the problem of
higher-order solitons. Our soliton matrices explicitly give all higher-order
multi-soliton solutions to the nonlinear partial differential equations
integrable through the matrix Riemann-Hilbert problem. We have applied these
general results to the three-wave interaction system, and derived new classes
of higher-order soliton and two-soliton solutions, in complement to those from
our previous publication [Stud. Appl. Math. \textbf{110}, 297 (2003)], where
only the elementary higher-order zeros were considered. The higher-order
solitons corresponding to non-elementary zeros generically describe the
simultaneous breakup of a pumping wave into the other two components
( and ) and merger of and waves into the pumping
wave. The two-soliton solutions corresponding to two simple zeros generically
describe the breakup of the pumping wave into the and
components, and the reverse process. In the non-generic cases, these
two-soliton solutions could describe the elastic interaction of the and
waves, thus reproducing previous results obtained by Zakharov and Manakov
[Zh. Eksp. Teor. Fiz. \textbf{69}, 1654 (1975)] and Kaup [Stud. Appl. Math.
\textbf{55}, 9 (1976)].Comment: To appear in J. Math. Phy
J-spectral factorization and equalizing vectors
For the Wiener class of matrix-valued functions we provide necessary and sufficient conditions for the existence of a -spectral factorization. One of these conditions is in terms of equalizing vectors. A second one states that the existence of a -spectral factorization is equivalent to the invertibility of the Toeplitz operator associated to the matrix to be factorized. Our proofs are simple and only use standard results of general factorization theory. Note that we do not use a state space representation of the system. However, we make the connection with the known results for the Pritchard-Salamon class of systems where an equivalent condition with the solvability of an algebraic Riccati equation is given. For Riesz-spectral systems another necessary and sufficient conditions for the existence of a -spectral factorization in terms of the Hamiltonian is added
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