| The spectrum of the perturbed shift operator $T$, $T: f(n)to f(n+1)+ a(n)f(n)$, in $ell^(bf Z)$ is considered for $a(n)$ taking a finite set of values. It is proven that if all values of the function $a(n)$ have uniform frequencies on $bf Z$ then the essential part of the spectrum is continuous and fills a lemniscate. |
Keywords
Jacobi interpolation series, lemniscate, shift operator, spectrum
Math Review Classification
Primary 47B39
; Secondary 47A10
Last Updated
24.05.2001
Length
14 pages
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