Reflexive Space Research Articles

S-Iteration inertial subgradient extragradient method for variational inequality and fixed point problems

In developing iterative methods for approximating solutions of optimization problems, one of the major goals of researchers is to construct efficient iterative schemes. Over the years, different techniques have been devised by authors to achieve this goal. In this paper, we study a non-Lipschitz pseudomonotone variational inequality problem with common fixed points constraint of Bregman quasi-nonexpansive mappings. We introduce a new iterative method for approximating the solution of this problem in a more general framework of reflexive Banach spaces. Our method employs several techniques to achieve high level of efficiency. One of the techniques employed is the S-iteration process, a method known to be highly efficient in comparison with several of the well-known methods. Moreover, our proposed algorithm utilizes the inertial technique and a non-monotonic self-adaptive step size to guarantee high rate of convergence and easy implementation. Unlike several of the existing results on variational inequality problem with non-Lipschitz operator, the design of our method does not involve any linesearch technique. We obtain strong convergence result for the proposed algorithm without the sequentially weakly continuity condition often assumed by authors to guarantee convergence when solving pseudomonotone variational inequality problems. Furthermore, we apply our result to study utility-based bandwidth allocation problem and image restoration problem. Finally, we present several numerical experiments to demonstrate the efficiency of our proposed method in comparison with existing state-of-the-art methods. Our result extends and improves several of the recently announced results in this direction in the literature.

A theoretical view of existence results by using fixed point theory for quasi-variational inequalities

In this paper, we present new existence results for the quasi-variational inequality problem (QV I) in reflexive Banach spaces using the fixed point method with quasi-monotonicity and local upper sign-continuity assumptions. These results improve upon previous ones which only required a weaker monotonicity condition and did not impose compactness on the involved set.

One-step Bregman projection methods for solving variational inequalities in reflexive Banach spaces

ABSTRACT We study two Bregman projection methods for solving variational inequality problems in real reflexive Banach spaces. Our methods have simple and elegant structures, and they require only one Bregman projection onto the feasible set and one evaluation of the cost operator at each iteration. We prove that these methods converge weakly when the cost operator is pseudomonotone on the entire space and that they converge strongly when the cost operator is strongly pseudomonotone only on the feasible set. Extensions of our proposed methods to mixed variational inequality problems are also given. Finally, we consider some examples regarding the implementation of our methods in comparisons with known methods in the literature.

Approximate Controllability of Non-autonomous Second Order Impulsive Functional Evolution Equations in Banach Spaces

This article investigates the approximate controllability of second order non-autonomous functional evolution equations involving non-instantaneous impulses and nonlocal conditions. First, we discuss the approximate controllability of second order linear system in detail, which lacks in the existing literature. Then, we derive sufficient conditions for approximate controllability of our system in separable reflexive Banach spaces via linear evolution operator, resolvent operator conditions, and Schauder’s fixed point theorem. Moreover, in this paper, we define proper identification of resolvent operator in Banach spaces. Finally, we provide two concrete examples to validate our results.

CONVERGENCE CRITERIA, WELL-POSEDNESS CONCEPTS AND APPLICATIONS

We consider an abstract problem P in a metric space X which has a unique solution u G X. Our aim in this current paper is two folds: first, to provide a convergence criterion to the solution of Problem P , that is, to give necessary and sufficient conditions on a sequence {un} C X which guarantee the convergence un ^ u in the space X; second, to find a Tyknonov triple T such that a sequence {un} C X is a T -approximating sequence if and only if it converges to u. The two problems stated above, associated to the original Problem P , are closely related. We illustrate how they can be solved in three particu­lar cases of Problem P: a variational inequality in a Hilbert space, a fixed point problem in a metric space and a minimization problem in a reflexive Banach space. For each of these problems we state and prove a convergence criterion that we use to define a convenient Tykhonov triple T which requires the condition stated above. We also show how the convergence criterion and the corresponding T -well posedness con­cept can be used to deduce convergence and classical well-posedness results, respectively.

What does Birkhoff--James orthogonality know about the norm?

It is shown that Birkhoff-James orthogonality knows everything about the smooth norms in reflexive Banach spaces and can also compute the dimensions of the underlying normed spaces.

Strong convergence analysis for solving quasi-monotone variational inequalities and fixed point problems in reflexive Banach spaces

Strong convergence analysis for solving quasi-monotone variational inequalities and fixed point problems in reflexive Banach spaces

Local separation, closedness and zero-dimensionality in quantale-valued reflexive spaces

In this paper, first, we introduce the category Q-RRel consisting of quantale-valued reflexive spaces and Q-monotone mappings, and prove that it is a normalized topological category over Set, the category of sets and functions. Furthermore, we characterize explicitly each of local Ti, i = 0, 1, 2 and PreT2 Q-reflexive spaces and examine the relationships among them. Finally, we give the characterizations of (strongly) closed subsets and zero-dimensional objects in this category.

Further study on second order nonlocal problems monitored by an operator

In this note we prove the existence of mild solutions for nonlocal problems governed by semilinear second order differential inclusions which involves a nonlinear term driven by an operator. A first result is obtained in suitable Banach spaces in the lack of compactness both on the fundamental operator, generated by the linear part, and on the nonlinear multivalued term. This purpose is achieved by combining a fixed point theorem, a selection theorem and a containment theorem. Further we provide another existence result in reflexive spaces by using the classical Hahn–Banach theorem and a new selection proposition, proved here, for a multimap guided by an operator. This setting allows us to remove some assumptions required in the previous existence theorem. As a consequence of this last result we obtain the controllability of a problem driven by a wave equation on which an appropriate perturbation acts.

Interpretation on nonlocal neutral functional differential equations with delay

<abstract><p>This work deals with the existence and continuous dependence of an integral solution for neutral integro-differential equations with a nonlocal condition. This result is established by using an integrated resolvent operator under conditions of Lipschitz continuity and uniqueness via the Banach fixed point technique. We also study the existence of a strict solution on reflexive and general Banach spaces. In the last section, an example is provided related to this theory.</p></abstract>

Generalized $ (f, \lambda) $-projection operator on closed nonconvex sets and its applications in reflexive smooth Banach spaces

<abstract><p>In this paper, we expanded from the convex case to the nonconvex case in the setting of reflexive smooth Banach spaces, the concept of the $ f $-generalized projection $ \pi^{f}_S:X^*\to S $ initially introduced for convex sets and convex functions in <sup>[<xref ref-type="bibr" rid="b19">19</xref>,<xref ref-type="bibr" rid="b20">20</xref>]</sup>. Indeed, we defined the $ (f, \lambda) $-generalized projection operator $ \pi^{f, \lambda}_S:X^*\to S $ from $ X^* $ onto a nonempty closed set $ S $. We proved many properties of $ \pi^{f, \lambda}_S $ for any closed (not necessarily convex) set $ S $ and for any lower semicontinuous function $ f $. Our principal results broaden the scope of numerous theorems established in <sup>[<xref ref-type="bibr" rid="b19">19</xref>,<xref ref-type="bibr" rid="b20">20</xref>]</sup> from the convex setting to the nonconvex setting. An application of our main results to solutions of nonconvex variational problems is stated at the end of the paper.</p></abstract>

Approximating Solutions of Monotone Variational Inclusion, Equilibrium and Fixed Point Problems of Certain Nonlinear Mappings in Banach Spaces

In this paper, motivated by the works of Timnak et al. [Filomat 31(15) (2017), 4673–4693], Ogbuisi and Izuchukwu [Numer. Funct. Anal. 40(13) (2019)] and some other related results in literature, we introduce an iterative algorithm and employ a Bregman distance approach for approximating a zero of the sum of two monotone operators, which is also a common solution of equilibrium problem involving pseudomonotone bifunction and a fixed point problem for an infinite family of Bregman quasi-nonexpansive mappings in the framework of a reflexive Banach space. Using our iterative algorithm, we state and prove a strong convergence result for approximating a common solution of the aforementioned problems. Furthermore, we give some applications of the consequences of our main result to convex minimization problem and variational inequality problem. Lastly, we display a numerical example to show the applicability of our main result. The result presented in this paper extends and complements many related results in the literature.

A Review of the Tsirleson's Space Norm

In most cases, the space of all sequences converging to zero or the space of bounded sequences is always embedded in complete normed linear spaces. This concept, however, was modified by B.S. Tsirelson by constructing reflexive complete normed linear spaces with monotone unconditional Schauder basis without embedded copies of sequences converging to zero or the space of bounded sequence. In this article, a relation with any four non-negative integers has been proved, and this concept is used to prove the triangle inequality of a slightly different Tsirelson’s type of norm in the space of all real sequences with finite support. Furthermore, all properties of the norm have been studied for a different type of norm function in the space of real sequences with finite support.

Approximate Birkhoff orthogonalities in normed spaces

In a normed space we characterize the approximate orthogonality in terms of extreme points of the closed unit ball in dual space. There is also another (and older) definition of an approximate orthogonality and therefore in this paper both approximate orthogonalities are compared. Moreover, we characterize the approximate orthogonality in the class of compact operators on a reflexive Banach space.

Infinitely many solutions for a class of fractional boundary value problem with $p$-Laplacian with impulsive effects

The existence of infinitely many solutions for a class of impulsive fractional boundary value problems with $p$-Laplacian with Neumann conditions is established. Our approach is based on recent variational methods for smooth functionals defined on reflexive Banach spaces. One example is presented to demonstrate the application of our main results.

Convergence theorem for split feasibility problem, equilibrium problem and zeroes of sum of monotone operators

The main purpose of this paper is to introduce a parallel iterative algorithm for approximating the solution of a split feasibility problem on the zero of monotone operators, generalized mixed equilibrium problem and fixed point problem. Using our algorithm, we state and prove a strong convergence theorem for approximating a common element in the set of solutions of a problem of finding zeroes of sum of two monotone operators,generalized mixed equilibrium problem and fixed point problem for a finite family of $\eta$-demimetric mappings in the frame work of a reflexive, strictly convex and smooth Banach spaces. We also give a numerical experiment applying our main result. Our result improves, extends and unifies other results in this direction in the literature.

A Corollary to a Triviality Theorem for Quasirepresentations of an Amenable Group in Reflexive Banach Spaces

A Corollary to a Triviality Theorem for Quasirepresentations of an Amenable Group in Reflexive Banach Spaces

From Calmness to Hoffman Constants for Linear Semi-infinite Inequality Systems

In this paper we focus on different---global, semilocal, and local---versions of Hoffman-type inequalities expressed in a variational form. In a first stage our analysis is developed for generic multifunctions between metric spaces, and we finally deal with the feasible set mapping associated with linear semi-infinite inequality systems (finitely many variables and possibly infinitely many constraints) parameterized by their right-hand sides. The Hoffman modulus is shown to coincide with the Lipschitz upper semicontinuity modulus and the supremum of calmness moduli when confined to multifunctions with a convex graph and closed images in a reflexive Banach space, which is the case for our feasible set mapping. Moreover, for this particular multifunction a formula---involving only the system's left-hand side---of the global Hoffman constant is derived, providing a generalization to our semi-infinite context of finite counterparts developed in the literature. In the particular case of locally polyhedral systems, the paper also provides a point-based formula for the (semilocal) Hoffman modulus in terms of the calmness moduli at certain feasible points (extreme points when the nominal feasible set contains no lines), yielding a practically tractable expression for finite systems.

Recurrence properties for linear dynamical systems: An approach via invariant measures

We study different pointwise recurrence notions for linear dynamical systems from the Ergodic Theory point of view. We show that from any reiteratively recurrent vector x0, for an adjoint operator T on a separable dual Banach space X, one can construct a T-invariant probability measure which contains x0 in its support. This allows us to establish some equivalences, for these operators, between some strong pointwise recurrence notions which in general are completely distinguished. In particular, we show that (in our framework) reiterative recurrence coincides with frequent recurrence; for complex Hilbert spaces uniform recurrence coincides with the property of having a spanning family of unimodular eigenvectors; and the same happens for power-bounded operators on complex reflexive Banach spaces. These (surprising) properties are easily generalized to product and inverse dynamical systems, which implies some relations with the respective hypercyclicity notions. Finally we study how typical is an operator with a non-zero reiteratively recurrent vector in the sense of Baire category.

Measurable functional calculi and spectral theory in the reflexive Banach spaces

In this paper, we consider the spectral theory. More precisely, we study the spectral families and their corresponding operators on reflexive Banach spaces. Assume [Formula: see text] is a well-bounded operator on reflexive Lebesgue spaces then the operator [Formula: see text] is a scalar-type spectral operator. We establish that if a weak spectral family [Formula: see text] is concentrated on [Formula: see text] then there exists a linear well-bounded operator [Formula: see text] on the reflexive Banach space [Formula: see text], such that [Formula: see text] holds for all [Formula: see text] and [Formula: see text]. We prove that by assuming [Formula: see text] is a functional calculus on the measurable space [Formula: see text], then there are a semi-finite measure space [Formula: see text] and solitary operator [Formula: see text], and an injective pointwise continuous *-homomorphism [Formula: see text], such that [Formula: see text] holds for any operator of the multiplication [Formula: see text] that multiplies by function [Formula: see text].