Semigroups Generated by Ordinary Differential Operators in L 1(I)*

In this paper we give necessary and sufficient conditions for the existence of a C> ₀-semigroup in L ¹(I) (I real interval) generated by a second-order differential operator when suitable boundary conditions at the endpoints are imposed.     

Approximation of infinite-dimensional fleming-viot diffusions

The aim of this article is the approximation of a class of infinite-dimensional diffusions occurring in population genetics using a semigroup approach and a suitable sequence of Bernstein-Schnabl type operators which are associated with assigned sequences of positive real numbers.     

Qualitative properties of a class of Fleming-Viot operators

We indicate some qualitative properties of Fleming--Viot second order differential operators on the d-dimensional simplex, such as an inductive characterization of its domain and some spectral properties connected with the asymptotic behavior of the generated semigroup. These properties turn out to be very useful in the approximation of the solution of the evolution problem associated with Fleming--Viot operators, which are very important as diffusion models in population genetics.     

Rate of Convergence in Trotter’s Approximation Theorem

We give a quantitative estimate of the convergence in Trotter’s approximation theorem on the convergence of iterates of linear operators to an assigned semigroup. An application is given concerning the classical Bernstein operator on the d-dimensional simplex.      

Degenerate Self-adjoint Evolution Equations on the Unit Interval

a∈ C ¹([0,1]) vanishing only at 0, 1 and b∈ C ([0,1]), we study existence, qualitative properties, asymptotic behaviour and approximation of the solutions of the degenerate evolution problem u _t = (au _z ) _z - bu in ]0,1[x]0, + ∞[, with u(x,0) = u ₀ (x) and boundary conditions a(x)u _x (x,t) → 0 as x → 0,1, t > 0.     

Bernstein-Type Operators on the Half Line

We define Bernstein-type operators on the half line [0, +[ by means of two sequences of strictly positive real numbers. After studying their approximation properties, we also establish a Voronovskaja-type result with respect to a suitable weighted norm.     

General binomial-type coefficients in the sequence of Bernstein operators

In this paper we study the sequence of Bernstein operators in the case when the binomial coefficients are substituted by general ones satisfying a similar recursive rule. Besides the characterization of the convergence and the approximation properties of the sequence of operators obtained in this manner, the main application regards the approximation of the solutions of suitable second-order parabolic problems. Work performed under the auspices of G. N. A. F. A. (C. N. R.) and M. U. R. S. T.     

Korovkin-type approximation in spaces of vector-valued and set-valued functions

We consider some Korovkin-type approximation results for sequences of linear continuous operators in spaces of vector-valued and set-valued continuous functions without assuming the existence of the limit operator. Even in spaces of real continuous functions, where similar results have already been established, we replace the positivity assumption with a weaker condition. We also give some quantitative estimate of the convergence and some applications where previous results cannot be applied.