2019
Том 71
№ 7

# Approximation of unbounded operators by bounded operators in a Hilbert space

Abstract

We determine the best approximation of an arbitrary power $A^k$ of an unbounded self-adjoint operator $A$ in a Hilbert space $H$ on the class $\{x ∈ D(A^r ) : ∥A^r x∥ ≤ 1\},\; k < r$.

English version (Springer): Ukrainian Mathematical Journal 61 (2009), no. 2, pp 179-187.

Citation Example: Babenko V. F., Bilichenko R. O. Approximation of unbounded operators by bounded operators in a Hilbert space // Ukr. Mat. Zh. - 2009. - 61, № 2. - pp. 147-153.

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