Geodesic
On the best approximation of the infinitesimal generator of a contraction semigroup in a Hilbert space
Ural mathematical journal, Tome 3 (2017) no. 2, pp. 40-45 Cet article a éte moissonné depuis la source Math-Net.Ru

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Let $A$ be the infinitesimal generator of a strongly continuous contraction semigroup in a Hilbert space $H$. We give an upper estimate for the best approximation of the operator $A$ by bounded linear operators with a prescribed norm in the space $H$ on the class $Q_2 = \{x\in \mathcal{D}(A^2) : \|A^2 x\| \leq 1\}$, where $\mathcal D(A^2)$ denotes the domain of $A^2$.
Keywords: Contraction semigroup, Infinitesimal generator, Stechkin's problem. 
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     title = {On the best approximation of the infinitesimal generator of a contraction semigroup in a {Hilbert} space},
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Elena E. Berdysheva; Maria A. Filatova. On the best approximation of the infinitesimal generator of a contraction semigroup in a Hilbert space. Ural mathematical journal, Tome 3 (2017) no. 2, pp. 40-45. http://geodesic.mathdoc.fr/item/UMJ_2017_3_2_a5/

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