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Fractional powers of generators of equicontinuous semigroups and fractional derivatives

Published online by Cambridge University Press:  09 April 2009

Oscar E. Lanford III
Affiliation:
IHES 91440 Bures-sur-Yvette, France
Derek W. Robinson
Affiliation:
Mathematics Department, Institute of Advanced Studies, Australian National University, Canberra, Australia
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Abstract

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We analyze fractional powers Hα, α > 0, of the generators H of uniformly bounded locally equicontinuous semigroups S. The Hα are defined as the αth derivative δα of the Dirac measure δ evaluated on S. We demonstrate that the Hα are closed operators with the natural properties of fractional powers, for example, HαHβ = Hα+β for α, β > 0, and (Hα)β = Hαβ for 1 > α > 0 and β > 0. We establish that Hα can be evaluated by the Balakrishnan-Lions-Peetre algorithm where m is an integer larger than α, Cα, m is a suitable constant, and the limit exists in the appropriate topology if, and only if, x ∈ D(Hα). Finally we prove that H is the fractional derivation of S in the sense where the limit again exists if, and only if, x ∈ D(Hα).

Type
Research Article
Copyright
Copyright © Australian Mathematical Society 1989

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