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On the abstract Cauchy problem in the case of constant domains

Paolo Acquistapace, Brunello Terreni (1984)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

Si studiano esistenza, unicità e regolarità delle soluzioni strette, classiche e forti u ∈ 𝐂 ⁢ ( [ 0 , T ] , E ) dell'equazione di evoluzione non autonoma u ′ ⁢ ( t ) - A ⁢ ( t ) ⁢ u ⁢ ( t ) = f ⁢ ( t ) con il dato iniziale u ⁢ ( 0 ) = x , in uno spazio di Banach E . Gli operatori A ⁢ ( t ) sono generatori infinitesimali di semi-gruppi analitici ed hanno dominio indipendente da t e non necessariamente denso in E . Si danno condizioni necessarie e sufficienti per l'esistenza e la regolarità hölderiana della soluzione e della sua derivata.

On the algebraic structure of the unitary group.

Éric Ricard, Christian Rosendal (2007)

Collectanea Mathematica

We consider the unitary group U of complex, separable, infinite-dimensional Hilbert space as a discrete group. It is proved that, whenever U acts by isometries on a metric space, every orbit is bounded. Equivalently, U is not the union of a countable chain of proper subgroups, and whenever E ⊆ U generates U, it does so by words of a fixed finite length.

On the asymptotic convergence of the polynomial collocation method for singular integral equations and periodic pseudodifferential equations

A. I. Fedotov (2002)

Archivum Mathematicum

We prove the convergence of polynomial collocation method for periodic singular integral, pseudodifferential and the systems of pseudodifferential equations in Sobolev spaces H s via the equivalence between the collocation and modified Galerkin methods. The boundness of the Lagrange interpolation operator in this spaces when s > 1 / 2 allows to obtain the optimal error estimate for the approximate solution i.e. it has the same rate as the best approximation of the exact solution by the polynomials.

Currently displaying 761 – 780 of 1576