Opuscula Math. 41, no. 6 (2021), 861-879
https://doi.org/10.7494/OpMath.2021.41.6.861

 
Opuscula Mathematica

Discrete spectra for some complex infinite band matrices

Maria Malejki

Abstract. Under suitable assumptions the eigenvalues for an unbounded discrete operator \(A\) in \(l_2\), given by an infinite complex band-type matrix, are approximated by the eigenvalues of its orthogonal truncations. Let \[\Lambda (A)=\{\lambda \in {\rm Lim}_{n\to \infty} \lambda _n : \lambda _n \text{ is an eigenvalue of } A_n \text{ for } n \geq 1 \},\] where \({\rm Lim}_{n\to \infty} \lambda_n\) is the set of all limit points of the sequence \((\lambda_n)\) and \(A_n\) is a finite dimensional orthogonal truncation of \(A\). The aim of this article is to provide the conditions that are sufficient for the relations \(\sigma(A) \subset \Lambda(A)\) or \(\Lambda (A) \subset \sigma (A)\) to be satisfied for the band operator \(A\).

Keywords: unbounded operator, band-type matrix, complex tridiagonal matrix, discrete spectrum, eigenvalue, limit points of eigenvalues.

Mathematics Subject Classification: 47B36, 47B37, 47A25, 47A75, 15A18.

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  • Communicated by Andrei Shkalikov.
  • Received: 2021-05-31.
  • Revised: 2021-08-20.
  • Accepted: 2021-10-08.
  • Published online: 2021-11-29.
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Cite this article as:
Maria Malejki, Discrete spectra for some complex infinite band matrices, Opuscula Math. 41, no. 6 (2021), 861-879, https://doi.org/10.7494/OpMath.2021.41.6.861

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