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A new class of positive linear operators preserving logarithmic functions

Laura Angeloni, Danilo Costarelli and Chiara Darielli

Vol. 8 (2026), No. 3, 755–778
Abstract

We introduce a new class of positive linear operators that generalize the classical Bernstein operators. Specifically, we construct a sequence of operators that preserve the logarithmic function ln (1 + μ + x), with μ > 0 and x [0,1]. We prove pointwise and uniform convergence and we derive a quantitative estimate of the approximation error in terms of the modulus of continuity. We also obtain a Voronovskaja-type asymptotic formula that is used to establish saturation results and inverse theorems. In particular, the saturation class of the considered approximation process is characterized by solving a second order differential equation. Shape-preserving properties, such as monotonicity, concavity and variation diminishing, are also investigated. Finally, a simple application to signal denoising is addressed.

Keywords
asymptotic approximation, positive linear operators, logarithm preservation, constructive approximation, saturation by solving differential problems, shape preserving, denoising
Mathematical Subject Classification
Primary: 41A25, 41A30, 41A60
Milestones
Received: 29 August 2025
Revised: 12 March 2026
Accepted: 13 July 2026
Published: 12 September 2026
Authors
Laura Angeloni
Department of Mathematics and Computer Science
University of Perugia
Perugia
Italy
Danilo Costarelli
Department of Mathematics and Computer Science
University of Perugia
Perugia
Italy
Chiara Darielli
Department of Mathematics and Computer Science
University of Firenze
Firenze
Italy