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Envelopes for sets and functions: regularization and generalized conjugacy

Abstract : Let X be a vector space and let phi : X -> R boolean OR {-infinity; +infinity} be an extended real-valued function. For every function f : X X -> R boolean OR {-infinity; +infinity}, let us define the phi-envelope of f by f phi(x) = sup(y is an element of X) phi(x - y) divided by f(y), where divided by denotes the lower subtraction in R boolean OR {-infinity, +infinity}. The main purpose of this paper is to study in great detail the properties of the important generalized conjugation map f -> f(phi). When the function ' is closed and convex, phi-envelopes can be expressed as Legendre-Fenchel conjugates. By particularizing with phi = (1/p lambda)parallel to.parallel to(p), for lambda > 0 and p >= 1, this allows us to derive new expressions of the Klee envelopes with index lambda and power p. Links between phi-envelopes and Legendre-Fenchel conjugates are also explored when -phi is closed and convex. The case of Moreau envelopes is examined as a particular case. In addition to the phi-envelopes of functions, a parallel notion of envelope is introduced for subsets of X. Given subsets Lambda, C boolean OR X, we define the 3 -envelope of C as C-Lambda = boolean AND(x is an element of C) (x + Lambda). Connections between the transform C -> C-Lambda and the aforestated phi-conjugation are investigated.
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Soumis le : mardi 25 avril 2017 - 17:47:34
Dernière modification le : mercredi 3 novembre 2021 - 07:39:25



Alexandre Cabot, Abderrahim Jourani, Lionel Thibault. Envelopes for sets and functions: regularization and generalized conjugacy. Mathematika, University College London, 2017, 63 (02), pp.383 - 432. ⟨10.1112/S0025579316000309⟩. ⟨hal-01514170⟩



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