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Regular fractional iteration of convex functions

Marek Kuczma (1980)

Annales Polonici Mathematici

The existence of a unique C 1 solution φ of equation (1) is proved under the condition that f: I → I is convex or concave and of class C 1 in I, 0 < f(x) < x in I*, and f’(x) > 0 in I. Here I = [0, a] or [0, a), 0 < a ≤ ∞, and I* = I 0.

Regular mappings between dimensions

Guy David, Stephen Semmes (2000)

Publicacions Matemàtiques

The notions of Lipschitz and bilipschitz mappings provide classes of mappings connected to the geometry of metric spaces in certain ways. A notion between these two is given by regular mappings (reviewed in Section 1), in which some non-bilipschitz behavior is allowed, but with limitations on this, and in a quantitative way. In this paper we look at a class of mappings called (s, t)-regular mappings. These mappings are the same as ordinary regular mappings when s = t, but otherwise they behave somewhat...

Regularity of convex functions on Heisenberg groups

Zoltán M. Balogh, Matthieu Rickly (2003)

Annali della Scuola Normale Superiore di Pisa - Classe di Scienze

We discuss differentiability properties of convex functions on Heisenberg groups. We show that the notions of horizontal convexity (h-convexity) and viscosity convexity (v-convexity) are equivalent and that h-convex functions are locally Lipschitz continuous. Finally we exhibit Weierstrass-type h-convex functions which are nowhere differentiable in the vertical direction on a dense set or on a Cantor set of vertical lines.

Regularity of the Hardy-Littlewood maximal operator on block decreasing functions

J. M. Aldaz, F. J. Pérez Lázaro (2009)

Studia Mathematica

We study the Hardy-Littlewood maximal operator defined via an unconditional norm, acting on block decreasing functions. We show that the uncentered maximal operator maps block decreasing functions of special bounded variation to functions with integrable distributional derivatives, thus improving their regularity. In the special case of the maximal operator defined by the -norm, that is, by averaging over cubes, the result extends to block decreasing functions of bounded variation, not necessarily...

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