Approximation by semi-Fredholm operators

Galaz-Fontes, Fernando

doi:10.1090/S0002-9939-1994-1197536-2

Approximation by semi-Fredholm operators
HTML articles powered by AMS MathViewer

by Fernando Galaz-Fontes PDF

Proc. Amer. Math. Soc. 120 (1994), 1219-1222 Request permission

Abstract:

We present a simple approach for calculating some known distances from a bounded operator defined on a separable Hilbert space to certain sets related to semi-Fredholm operators.

References

Approximation by Hilbert space operators

Richard Bouldin, The essential minimum modulus, Indiana Univ. Math. J. 30 (1981), no. 4, 513–517. MR 620264, DOI 10.1512/iumj.1981.30.30042
Richard Bouldin, The distance to operators with a fixed index, Acta Sci. Math. (Szeged) 54 (1990), no. 1-2, 139–143. MR 1073428
Richard Bouldin, Approximation by operators with fixed nullity, Proc. Amer. Math. Soc. 103 (1988), no. 1, 141–144. MR 938658, DOI 10.1090/S0002-9939-1988-0938658-5
S. R. Caradus, W. E. Pfaffenberger, and Bertram Yood, Calkin algebras and algebras of operators on Banach spaces, Lecture Notes in Pure and Applied Mathematics, Vol. 9, Marcel Dekker, Inc., New York, 1974. MR 0415345
Saichi Izumino and Yoshinobu Kato, The closure of invertible operators on a Hilbert space, Acta Sci. Math. (Szeged) 49 (1985), no. 1-4, 321–327. MR 839947
Pei Yuan Wu, Approximation by invertible and noninvertible operators, J. Approx. Theory 56 (1989), no. 3, 267–276. MR 990341, DOI 10.1016/0021-9045(89)90116-0
Jaroslav Zemánek, Geometric interpretation of the essential minimum modulus, Invariant subspaces and other topics (Timişoara/Herculane, 1981), Operator Theory: Advances and Applications, vol. 6, Birkhäuser, Basel-Boston, Mass., 1982, pp. 225–227. MR 685467