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Convex transformations with Banach lattice range.

Roman Ger (1987)

Stochastica

A closed epigraph theorem for Jensen-convex mappings with values in Banach lattices with a strong unit is established. This allows one to reduce the examination of continuity of vector valued transformations to the case of convex real functionals. In particular, it is shown that a weakly continuous Jensen-convex mapping is continuous. A number of corollaries follow; among them, a characterization of continuous vector-valued convex transformations is given that answers a question raised by Ih-Ching...

Convexity and almost convexity in groups

Witold Jarczyk (2013)

Banach Center Publications

We give a review of results proved and published mostly in recent years, concerning real-valued convex functions as well as almost convex functions defined on a (not necessarily convex) subset of a group. Analogues of such classical results as the theorems of Jensen, Bernstein-Doetsch, Blumberg-Sierpiński, Ostrowski, and Mehdi are presented. A version of the Hahn-Banach theorem with a convex control function is proved, too. We also study some questions specific for the group setting, for instance...

Convex-like inequality, homogeneity, subadditivity, and a characterization of L p -norm

Janusz Matkowski, Marek Pycia (1995)

Annales Polonici Mathematici

Let a and b be fixed real numbers such that 0 < mina,b < 1 < a + b. We prove that every function f:(0,∞) → ℝ satisfying f(as + bt) ≤ af(s) + bf(t), s,t > 0, and such that l i m s u p t 0 + f ( t ) 0 must be of the form f(t) = f(1)t, t > 0. This improves an earlier result in [5] where, in particular, f is assumed to be nonnegative. Some generalizations for functions defined on cones in linear spaces are given. We apply these results to give a new characterization of the L p -norm.

Critères de convexité et inégalités intégrales

Serge Dubuc (1977)

Annales de l'institut Fourier

Pour trois fonctions non-négatives intégrables sur R n , f , g et h , telles que ( h ( x + y ) ) - 1 / n ( f ( x ) ) - 1 / n + ( g ( y ) ) - 1 / n , Borelll a établi l’inégalité h ( z ) d z min f ( x ) d x , g ( y ) d y ) . Nous déterminons les conditions précises où l’inégalité sera stricte. La clef de cette analyse est une nouvelle caractérisation des fonctions convexes mesurables.

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