1. Introduction
Let
be a real Banach space with its dual
. Let
be a nonempty closed convex subset of
and
denote the duality pairing between
and
. The variational inequality problem (VIP) with respect to
is a problem of finding
such that
in which the operator
maps
to
. We write
to represent the set of (
1) solutions. Variational inequality theory, independently developed in the mechanics and potential theory by Stampacchia and Fichera in the early 1960s (see [
1,
2]), can be used broadly to treat a wide class of unrelated linear and nonlinear problems in elasticity, economics, transportation, optimization, control theory, and engineering sciences. The development of variational inequality theory can be understood as the simultaneous pursuit of two different fields of research. Basic facts on the qualitative behavior of solutions to important kinds of issues are disclosed in the first aspect. However, it also makes it possible for us to develop highly efficient and powerful numerical techniques to deal with boundary value problems, including unilateral, moving, free, and obstacle problems (see [
3]). It is commonly known that
is equivalent to the fixed-point problem:
where a metric projection onto
is denoted by
and
is any positive real number. Solving
has been approached in a variety of ways recently (see [
4,
5,
6,
7,
8,
9,
10,
11,
12,
13]). The gradient projection method (GPM) is the most basic projection method. The general concept of expanding the GPM to solve the
minimization issue pertaining to
is provided by
where the gradient function is
and the positive real sequence
satisfies a given condition. The GPM is a direct expansion of the procedure in (
2). It involves replacing operator
F with the gradient function in order to produce a sequence
in the way that follows:
Nevertheless, this method’s convergence necessitates a somewhat strong assumption that the operators are either strongly monotone or inversely monotonous. To loosen this constraint, the extragradient method (EM) for a monotone and
L-Lipschitz continuous mapping
was suggested by Korpelvich [
14] and Antipin [
15] in finite-dimensional Euclidean spaces.
where
. The sequence
produced by the EM (
3) converges to an element of
if
is not empty. Note that each iteration in the EM requires the computation of two projections into the feasible set
. Should the set
not be simple, implementing the EM becomes exceedingly complex and costly. Additionally, we stress that the stepsize defined by the process is excessively small and lowers the technique’s convergence rate. Moreover, the method (
3) requires a prior estimate of the Lipschitz constant, which is frequently difficult to estimate. To the best of our knowledge, these shortcomings can be addressed in certain ways. The first is the subgradient extragradient method (SEGM) [
9], which was proposed by Censor et al. In this approach, a projection onto a certain constructible half-space is used in place of the second projection onto
. Their approach takes this form:
where
.
The second approach is Tseng’s method from [
16]. Their approach takes this form:
where
.
It is important to mention that the SEGM and TM algorithms explained earlier merely require the computation of a single projection onto
in each iteration, which has the potential to enhance the performance of these algorithms. Numerous researchers have made enhancements to the SEGM and TM through various approaches (refer to [
4,
7,
9,
16,
17,
18] and the related references). We want to emphasize that both methods (SEGM and TM) have been extensively studied by authors in the context of real Hilbert and Banach spaces. One of the most effective strategies to accelerate the rate of convergence for iterative algorithms is to incorporate the inertial term into the iterative scheme. This term, denoted by
, serves as a remarkable tool for enhancing the performance of the algorithm and is known for its favorable convergence properties. Consequently, there is a growing interest among researchers working in this field (see [
4,
19,
20,
21,
22,
23]). The concept of the inertial extrapolation method was initially introduced by Polyak [
24] and was inspired by an implicit discretization of a second-order-in-time dissipative dynamical system, commonly referred to as the “heavy ball with friction”.
when
and
are differentiable. The discretization of the system (
6) allows for the determination of the following term using
:
where the step-size is denoted by
j. The following iterative algorithm is produced by Equation (
7):
where the inertial approach
and
are used to accelerate the convergence of the sequence produced by (
8). Using the proximal point algorithm (PPA), also known as the inertial PPA, Alvarez and Attouch used the inertial extrapolation method to set a general maximal monotone operator.
Their demonstration showed that if
is non-decreasing and
, then
Afterward, a weak convergence of Algorithm (
9) to a zero of
is achieved. For
, more specifically, condition (
10) holds true. An initial factor is denoted by
.
The inertial extrapolation approach in Banach space has been updated by a number of writers by leaving out the calculation of the difference between the norms of the two neighboring iterates,
and
. Because of the geometry of the space, the inertial term must be modified when approximating solutions of various optimization problems using the inertial extrapolation method in Banach space using either the viscosity or Halpern method (see [
7,
20,
25] and the references therein). The hybrid and shrinking procedures used in the Banach space setting is the only scenario in which the inertial terms remain unchanged (see [
4,
22,
23]). As far as we are aware, there is not a result for the inertial extrapolation method in Banach space without utilizing the Halpern method modification.
Question 1: Without computing the difference between the norms of the two adjacent iterates, and , can we introduce an inertial Halpern method combined with the Tseng procedure for approximating the outcome of VIP in the context of p-uniformly convex real Banach spaces that are also uniformly smooth?
We propose a modified Halpern inertial iterative method, inspired by the work of [
15,
16,
17,
18] and others, combined with a Tseng-type technique to find a common solution of the pseudomonotone variational inequality problem and the fixed-point problem of Bregman strongly nonexpansive mapping in the context of uniformly smooth,
p-uniformly real Banach space. We provide a strong convergence result for approximating the solution of the aforementioned problems using our iterative method. We stress that our iterative approach does not require any prior knowledge about the operator standard because of its architecture. To demonstrate the effectiveness of our solution, we provide a few numerical examples. Numerous relevant results in the literature are extended and enhanced by the results reported in this work.
2. Preliminaries
We state some known and useful results which will be needed in the proof of our main theorem. In the sequel, we denote strong and weak convergence by “→” and “⇀”, respectively.
Given a Banach space
, let its dual be
. It is argued that an operator
is
-Lipschitz if for all
,
where two constants are
and
. The operator
is called
L-Lipschitz if
.
Suppose there is a nonempty set . Next, let be a mapping. Then, for every , is
- (a)
monotone on if
- (b)
pseudomonotone on if
- (c)
Lipschitz continuous on if there is a number such that ;
- (d)
weakly sequentially continuous if is implied for all such that .
Given a real Banach space and a function the function g is defined as follows:
- (i)
Gâteaux differentiable at
denoted by
or
if there exists an element
v of
such that
where
g is
Gâteaux differentiable on
if
g is
Gâteaux differentiable at each
- (ii)
weakly lower semicontinuous at if implies . g is weakly lower semicontinuous on if g is weakly lower semicontinuous at each
Denote the unit sphere of
as
. The function
indicates the modulus of convexity described by
If, for every
,
, then
is considered uniformly convex. When
,
is said to have a modulus of convexity of power type
p, meaning that it is
p-uniformly convex. If
, for any
,
. Keep in mind that any spaces that are
p-uniformly convex are uniformly convex. For
, the function
is the modulus of smoothness. It is defined by
Uniform smoothness of the space
is defined as
as
. Assume
. If, for every
, there exists
such that
, then a Banach space
is
q-uniformly smooth. According to [
26],
is
p-uniformly convex if and only if
is
q-uniformly smooth, where
p and
q satisfy
.
Considering a real number
, the generalized duality mapping
can be defined as follows:
where
represents the duality pairing between
and
elements. Specifically, the normalized duality mapping is denoted by
if
. Assuming that
is uniformly smooth and p-uniformly convex,
is both uniformly smooth and
q-uniformly convex. Here,
is a one-to-one, single-valued generalized duality mapping that satisfies the generalized duality mapping of
is
, and
. Moreover, the duality mapping
is norm-to-norm uniformly continuous on bounded subsets of
E if
is uniformly smooth (see [
27] for more information).
The Frenchel conjugate of
g, denoted by
, is defined as follows if
is a proper, lower semicontinuous, and convex function:
To represent the domain of
g, wewrite
. Since
and
, we may define and express the right-hand derivative of
g at
u in the direction of
v as follows:
Definition 1 ([
28]).
Given a convex function , let g be Gâteaux differentiable. is a function defined byknown as the Bregman distance with respect to g, where . It is commonly known that because
does not satisfy the symmetric and triangular inequality properties, and the Bregman distance
does not satisfy the properties of a metric. Furthermore, it is commonly known that, for
, the sub-differential of the functional
is the duality mapping
(see [
29]). It is possible to demonstrate that the three-point identity, or the following equality, is satisfied by using (
11):
Moreover, if
, where
, we obtain
Suppose there is a nonlinear mapping . Then, we have the following: Please check that intended meaning has been retained.
- (i)
An asymptotic fixed point of is defined as if contains a sequence that converges weakly to p, with the result that . By , we represent the set of asymptotic fixed points;
- (ii)
It is stated that
is Bregman relatively nonexpansive if
- (iii)
Bregman relatively nonexpansive
is stated to exist if for all
,
- (iv)
When
, then
is a Bregman strongly nonexpansive mapping (BSNE) if, for all
,
and for every bounded sequence
,
implies
Assume that
is a closed, nonempty, convex subset of
. The projection metric
is defined as
the one and only minimizer of the norm distance, which has the following variational inequality:
Additionally, the Bregman projection represented by
from
onto
satisfies the following property:
Assume that
and
are nonempty, closed, convex subsets of a
p-uniformly convex and uniformly smooth Banach space
. Then, the following claims are true [
26]:
We now present a few findings that support our main result.
Lemma 1 ([
29]).
Consider a Banach space with . There exists such that, if is q-uniformly smooth,Let u, v, and w be in . With , we therefore haveand Lemma 2 ([
30]).
Consider a p-uniformly convex Banach space, . For any , the relationship between the metric and the Bregman distance is as follows:For any , if , we have Young’s inequality, where is a fixed number. Lemma 3 ([
31]).
Consider a real p-uniformly smooth and convex Banach space, . Let us define asThe following claims hold:
- (i)
In the first variable, is nonnegative and convex.
- (ii)
.
- (iii)
.
Lemma 4 ([
26]).
Let be a real p-uniformly convex and uniformly smooth Banach space. Suppose that and are bounded sequences in . Then implies . Lemma 5 ([
32]).
Assume that is a real reflexive Banach space and that is a nonempty, closed, convex subset of . We also define as a continuous pseudomonotone mapping from into . In such a case, is convex and closed. Moreover, for any , if and only if . Lemma 6 ([
33]).
Define as a nonnegative real number and as a real number sequence in with the following condition: , and as a real number sequence. Suppose thatIf, for each subsequence of satisfying the condition, then 3. Main Result
Assumption 1. - (L1)
A nonempty, closed, and convex subset of is . is a p-uniformly convex real Banach space that is also uniformly smooth. Afterward, the definition of is as below:
where - (L2)
On , is pseudomonotone and L-Lipschitz continuous.
- (L3)
Given any , implies . This indicates that is weakly sequentially continuous.
- (L4)
In , is a positive sequence. is defined in (22), and , where is a sequence in such that . Both and is the relationship between and sequences in . , and since for all , and are nonnegative real numbers sequences. - (L5)
We indicate , a Bregman strongly nonexpansive mapping, by , where .
In this section, we present Algorithm 1 for finding a common solution to the pseudomonotone variational inequality problem and the fixed-point problem of Bregman strongly nonexpansive mapping by combining the Tseng and Halpern-type methods with inertial extrapolation:
Algorithm 1: Inertial Tseng-type method for pseudomonotone VIP. |
Initialization: Assume the following: , , and . Create the family of half spaces for using the current iteration .
and set
Iterative Steps: Calculate as follows:- Step 1.
Assuming that and for each iterate and , determine such that .
- Step 2.
When for a given , the problem VIP has been addressed. If not, proceed to step 3. - Step 3.
Stopping Criterion: For any , if and , then end the process. Alternatively, assign and go back to Step 1.
|
Remark 1. Note that is a VIP solution if (1) stops in a finite step of iterations. Therefore, we assume for the remainder of our demonstration that (1) generates an infinite sequence and continues without stopping in any finite number of iterations.
Remark 2. Suppose , then the stepsize in (1) is like the ones in [4,34,35]. Additionally, the stepsize used in (1) increases from iteration to iteration, reducing the reliance on the starting step size . As is a summable sequence, . For big n, the stepsize may not be growing. Remark 3. Unlike the inertial methods used in [4,19,20,22], the inertial method used in this article does not impose any tight conditions on Furthermore, we stress that the inertial approach in (1) is original, as defined by Polyak [24], and is neither relaxed nor modified. To the best of our knowledge, no one has used a Halpern approach to accomplish this in the framework of p-uniformly convex real Banach space that is also uniformly smooth. Remark 4. Based on the description of and , the fact that is apparent. Specifically, the subdifferential inequality yields, for each and , The notion of implies that We may then conclude that for all since for all i.
Lemma 7. If we assume that is the sequence defined in (26), then as well as . In this case, Proof. For any bounded subset of
with constant
is Lipschitz-continuous. Consequently, in the case of
we obtain
The sequence
has an upper bound of
and a lower bound of
since
is defined and mathematical induction is used. Similar to Lemma 3.1 in [
35], the remainder of the argument is presented. □
Lemma 8. Assume that (L1) through (L5) are true. Then, the sequences produced by (1), , and , are bounded.
Proof. If
, then (1) implies that
On applying Lemma 1, we obtain
By substituting (
29) into (
28), we obtain
By applying (
12), we obtain
Thus, we obtain from (
13) that
As a result of (
17) and the definition of
, it can be concluded that
which implies that
We obtain (
31) after substituting the previous inequality.
Given that
;
’s pseudomonotonicity property implies that
Therefore, (
32) generates
By applying (
26), we have
Given that
there is a
such that
As a result, we obtain from (
33) that
Since we have
, it follows from (
22), (
23), and (1) that
By combining (
35) and (
36), we can determine that
We can see from (
32) and (
37) that
Let
. Based on (L4), there exists
such that, for any
,
Therefore, for some constant
, we obtain from (
38) that
Thus, using (1) and (39), we arrive at
As a result, has a limit. , , and are therefore restricted by . We conclude that , and are bounded in light of Lemma 4. □
Lemma 9. Assume that Algorithm 1 produces the sequence , whose subsequence converges weakly to , and that Assumption A1 holds. Therefore, if .
Proof. Using (
17) and the concept of
, we obtain
or, equivalently,
Using the facts that
and
is norm-to-norm uniformly continuous on bounded subsets of
and fixing
permitting
, we obtain that
By considering the limit in (
41) as
, we obtain
Now, using the facts that
and
we see that
Then, we demonstrate that
. Moreover,
implies that
and then
It follows that
is bounded since
is Lipschitz continuous and
is bounded. Consequently, for any
i, there exists
such that
. Thus, we obtain
where
. Thus, using the weak continuity of
, we obtain that
Therefore, .
Assuming that
of positive numbers is such that
is declining and
as
, we indicate
is the lowest positive integer, such that, for each
,
Observe that
rises as
falls. Select a point in
,
such that
= 1. Consequently, (
43) becomes
By utilizing the pseudomonotone nature of
, we obtain
Following that, we demonstrate that
Since
and
are weakly sequentially continuous on
,
follows. If
, then
else, given the progressively weakly lower semicontinuous nature of
, we obtain
Since
,
, and
we have
and
Hence, it follows from (
44) that
Thus, for all
we obtain that
Therefore, applying Lemma 5, we conclude that □
Theorem 1. If is a sequence produced by (1), then converges strongly to where
Proof. Using Lemma 3 (iii), (1), and (39), we derive
Likewise, we can determine from (1) and (39) that
Let us now assume that there exists a subsequence
such that
Afterward, we obtain from (
46) that
It is clear that (
48) yields
More so, using (1) it follows that
Thus, it follows from (
48) that
This uniform continuity from norm to norm of
on bounded subsets of
now gives
Let
then
Consequently, by applying the knowledge that
T is BSNE, we derive that
which implies from Lemma 4 that
From (
49) and (
51), we obtain
Using (1) and (
53), we obtain
By applying Lemma 4, we obtain
Hence, we conclude from (
55) and (
57) that
Given that
is bounded,
has a subsequence that converges weakly to
. There exist subsequences
of
and
of
that converge weakly to
, respectively, by applying (
48) and (
49). In light of this,
can be obtained by applying (
54). Additionally,
may be obtained by applying (
48) and Lemma 9. Thus, we deduce that
In the event that
, we have from (
45) that
Since
is a subsequence of
, then we have from (
17) that
Hence, since (
58) holds, then
Therefore, using Lemma 6 and (
60) in (
59), we obtain that
as
and from Lemma 2, we know that
Hence,
, where
. □