On k-strong convexity in banach spaces
Article, Journal of Convex Analysis, 2021,
View abstract ⏷
We introduce and study the notion of k-strong convexity in Banach spaces. It is a generalization of the notion of strong convexity first studied by Fan and Glicksberg. A Banach space is said to be k-strongly convex if it is reflexive, k-strictly convex and has the Kadec-Klee property. We use the idea of k-dimensional diameter to give several characterizations of k-strong convexity. Further, we study k-strict convexity and k-strong convexity in some products of Banach spaces. Finally, we give characterizations of k-uniform convexity that distinguish it from k-strong convexity.
Existence of fixed points for pointwise eventually asymptotically nonexpansive mappings
Article, Applied General Topology, 2019, DOI Link
View abstract ⏷
Kirk introduced the notion of pointwise eventually asymptotically non- expansive mappings and proved that uniformly convex Banach spaces have the fixed point property for pointwise eventually asymptotically nonexpansive maps. Further, Kirk raised the following question: “Does a Banach space X have the fixed point property for pointwise eventually asymptotically nonexpansive mappings whenever X has the fixed point property for nonexpansive mappings?”. In this paper, we prove that a Banach space X has the fixed point property for pointwise eventually asymptotically nonexpansive maps if X has uniform normal sturcture or X is uniformly convex in every direction with the Maluta constant D(X) < 1. Also, we study the asymptotic behavior of the sequence {T nx} for a pointwise eventually asymptotically nonexpansive map T defined on a nonempty weakly compact convex subset K of a Banach space X whenever X satisfies the uniform Opial condition or X has a weakly continuous duality map.
Some fixed point theorems on non-convex sets
Article, Applied General Topology, 2017, DOI Link
View abstract ⏷
In this paper, we prove that if K is a nonempty weakly compact set in a Banach space X, T: K → K is a nonexpansive map satisfying (Formula presented.) for all x ϵ K and if X is 3−uniformly convex or X has the Opial property, then T has a fixed point in K.