数学物理学报(英文版) ›› 2025, Vol. 45 ›› Issue (4): 1597-1618.doi: 10.1007/s10473-025-0419-9

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GÂTEAUX DIRECTIONAL DIFFERENTIABILITY OF THE GENERALIZED METRIC PROJECTION IN BANACH SPACES

Jinlu LI   

  1. Department of Mathematics, Shawnee State University, 940 Second Street, Portsmouth, OH 45662, USA
  • 收稿日期:2024-03-04 出版日期:2025-10-10 发布日期:2025-10-10

GÂTEAUX DIRECTIONAL DIFFERENTIABILITY OF THE GENERALIZED METRIC PROJECTION IN BANACH SPACES

Jinlu LI   

  1. Department of Mathematics, Shawnee State University, 940 Second Street, Portsmouth, OH 45662, USA
  • Received:2024-03-04 Online:2025-10-10 Published:2025-10-10
  • About author:Jinlu LI, E-mail: jli@shawnee.edu

摘要: Let $X$ be a real uniformly convex and uniformly smooth Banach space and $C$ a nonempty closed and convex subset of $X$. Let $\Pi_C{:}~X\to C$ denote the generalized metric projection operator introduced by Alber in [1]. In this paper, we define the Gâteaux directional differentiability of $\Pi_{C.}$ We investigate some properties of the Gâteaux directional differentiability of $\Pi_C$. In particular, if $C$ is a closed ball, or a closed and convex cone (including proper closed subspaces), or a closed and convex cylinder, then, we give the exact representations of the directional derivatives of $\Pi_{C.}$ By comparing the results in [12] and this paper, we see the significant difference between the directional derivatives of the generalized metric projection operator $\Pi_{C}$ and the Gâteaux directional derivatives of the standard metric projection operator $P_{C.}$

关键词: uniformly convex and uniformly smooth Banach space, the generalized metric projection, directional differentiability of the generalized metric projection, directional derivative of the generalized metric projection

Abstract: Let $X$ be a real uniformly convex and uniformly smooth Banach space and $C$ a nonempty closed and convex subset of $X$. Let $\Pi_C{:}~X\to C$ denote the generalized metric projection operator introduced by Alber in [1]. In this paper, we define the Gâteaux directional differentiability of $\Pi_{C.}$ We investigate some properties of the Gâteaux directional differentiability of $\Pi_C$. In particular, if $C$ is a closed ball, or a closed and convex cone (including proper closed subspaces), or a closed and convex cylinder, then, we give the exact representations of the directional derivatives of $\Pi_{C.}$ By comparing the results in [12] and this paper, we see the significant difference between the directional derivatives of the generalized metric projection operator $\Pi_{C}$ and the Gâteaux directional derivatives of the standard metric projection operator $P_{C.}$

Key words: uniformly convex and uniformly smooth Banach space, the generalized metric projection, directional differentiability of the generalized metric projection, directional derivative of the generalized metric projection