Research Article
Ordered Convex Metric Spaces
Ismat Beg
Department of Mathematics and Statistical Sciences, Lahore School of Economics, Lahore 53200, Pakistan
Correspondence should be addressed to Ismat Beg; ibeg@lahoreschool.edu.pk
Received 30 August 2021; Revised 14 October 2021; Accepted 15 October 2021; Published 25 October 2021
Academic Editor: Alberto Fiorenza
Copyright © 2021 Ismat Beg. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The aim of this article is to introduce a new notion of ordered convex metric spaces and study some basic properties of these
spaces. Several characterizations of these spaces are proven that allow making geometric interpretations of the new concepts.
1. Introduction
Menger [1] initiated the study of convexity in metric spaces
which was further developed by many authors [2–4]. The
terms “metrically convex” and “convex metric space” are
due to [2]. Subsequently, Takahashi [5] introduced the notion
of convex metric spaces and studied their geometric proper-
ties. Takahashi also proved that all normed spaces and their
convex subsets are convex metric spaces and gave an example
of a convex metric space which is not embedded in any nor-
med/Banach space. Kirk [6] showed that a metric space of
hyperbolic type is a convex metric space. Afterward, Shimizu
and Takahashi [7] gave the concept of uniformly convex met-
ric space, studied its properties, and constructed examples of
a uniformly convex metric space. Beg [8] established some
inequalities in uniformly convex complete metric spaces
analogous to the parallelogram law in Hilbert spaces and their
applications. Beg [9] proved that a closed convex subset of
uniformly convex complete metric spaces is a Chebyshev
set. Recently, Abdelhakim [10] studied convex functions on
these spaces. The aim of this note is to further continue the
research in this direction by introducing the concept of
ordered convex metric spaces and study their structure.
We conclude with the plan of the paper. In Section 2, we
recall some basic notations and definitions from the existing
literature on convex metric spaces, order structure, and gen-
eral topology. In Section 3, we introduce the new concept of
ordered convex metric spaces and study some basic proper-
ties. Several characterizations of these spaces are also proven
that allow making geometric interpretations of the new con-
cepts Finally, Section 4 concludes with a summary statement.
2. Preliminaries
In this section, basic results about convex metric spaces and
order structure are given.
Definition 1 (see [5]). Let ðX, dÞ be a metric space and I =
½0, 1. A mapping ω : X × X × I ⟶ X is said to be a convex
structure on X if for each ða, b, λÞ ∈ X × X × I and u ∈ X,
du, ω a, b ; λ ð Þ ð Þ ≤ λdu, a ð Þ +1 − λ ð Þdu, b ð Þ: ð1Þ
Metric space ðX, dÞ together with the convex structure ω
is called a convex metric space. A nonempty subset K ⊂ X is
said to be convex if ωða, b ; λÞ ∈ K whenever ða, b, λÞ ∈ K ×
K × I .
Remark 2 (see [5, 10]). The convex metric space ðX, dÞ has
the following properties:
(i) wða, b ;1Þ = a, ωða, b ;0Þ = b, ωða, a ; λÞ = a
(ii) Open spheres Bða, rÞ = fb ∈ X : dða, bÞ < rg and
closed spheres B½a, r = fb ∈ X : dða, bÞ ≤ rg are
convex
(iii) If fK
α
: α ∈ Ag is a family of convex subsets of X,
then ∩ K
α
α∈A
is convex
Any normed space and a convex subset of a normed
space is a convex metric space. There are several examples
Hindawi
Journal of Function Spaces
Volume 2021, Article ID 7552451, 4 pages
https://doi.org/10.1155/2021/7552451