- Research
- Open access
- Published:
Demiclosed principle and convergence theorems for asymptotically strictly pseudononspreading mappings and mixed equilibrium problems
Fixed Point Theory and Applications volume 2014, Article number: 104 (2014)
Abstract
In this paper, the demiclosed principle for a k-asymptotically strictly pseudononspreading mapping is shown. Meanwhile, an iterative scheme is introduced to approximate a common element of the set of common fixed points of k-asymptotically strictly pseudononspreading mappings and the set of solutions of mixed equilibrium problems in Hilbert spaces, and some weak and strong convergence theorems are proved. The results presented in this paper improve and extend some recent corresponding results.
MSC:47H09, 47J25.
1 Introduction
Let H be a real Hilbert space with the inner product and the norm . Let C be a nonempty closed convex subset of H and be a bifunction, where R is the set of real numbers. The equilibrium problem (for short, EP) is to find such that
The set of solutions of EP is denoted by . Given a mapping , let for all . Then if and only if is a solution of the variational inequality for all , i.e., is a solution of the variational inequality.
Let be a function. The mixed equilibrium problem (for short, ) is to find such that
The set of solutions of is denoted by .
If , then mixed equilibrium problem (1.2) reduces to (1.1).
If , then mixed equilibrium problem (1.2) reduces to the following convex minimization problem:
The set of solutions of (1.3) is denoted by .
The mixed equilibrium problem (MEP) includes several important problems arising in physics, engineering, science optimization, economics, transportation, network and structural analysis, Nash equilibrium problems in noncooperative games and others. It has been shown that variational inequalities and mathematical programming problems can be viewed as a special realization of abstract equilibrium problems (e.g., [1, 2]). Many authors have proposed some useful methods to solve the EP, ; see, for instance, [1–8] and the references therein.
Let H be a real Hilbert space and C be a nonempty closed convex subset of H. Following Kohsaka and Takahashi [9–11], a mapping is said to be nonspreading if
It is easy to see that the above inequality is equivalent to
In 1967, Browder and Petryshyn [12] introduced the concept of k-strictly pseudononspreading mapping.
Definition 1.1 [12]
Let H be a real Hilbert space. A mapping is said to be k-strictly pseudononspreading if there exists such that
Clearly, every nonspreading mapping is k-strictly pseudononspreading.
In 2012, Osilike [13] introduced a class of nonspreading type mappings, which is more general than the mappings studied in [14] in Hilbert spaces, and proved some weak and strong convergence theorems in real Hilbert spaces. Recently, Chang [15] studied the multiple-set split feasibility problem for asymptotically strict pseudocontraction in the framework of infinite-dimensional Hilbert spaces.
Definition 1.2 [15]
Let H be a real Hilbert space. A mapping is said to be a k-asymptotically strict pseudocontraction if there exist a constant and a sequence with () such that
holds for all .
Definition 1.3 Let C be a nonempty subset of a real Hilbert space H. A mapping is said to be k-asymptotically strictly pseudononspreading if there exist a constant and a sequence with () such that
It is easy to see that the class of k-asymptotically strictly pseudononspreading mappings is more general than the classes of k-strictly pseudononspreading mappings and k-asymptotically strict pseudocontractions.
Example 1.4 Let with the norm defined by
and be an orthogonal subspace of X (i.e., , we have ). It is obvious that C is a nonempty closed convex subset of X. For each , we define the mapping by
Next we prove that T is a k-asymptotically strictly pseudononspreading mapping.
In fact, for any .
Case 1. If and , then we have , , and so inequality (1.4) holds for any .
Case 2. If and , then we have that , . This implies that
Therefore inequality (1.4) holds for any .
Case 3. If and , then we have that , . Therefore we obtain
So, inequality (1.4) holds for any .
Case 4. If and , then we have , . Hence we have
Thus inequality (1.4) still holds for any . Therefore the mapping defined by (1.5) is a k-asymptotically strictly pseudononspreading mapping.
A mapping is said to be uniformly L-Lipschitzian if there exists a constant such that for all ,
A Banach space E is said to satisfy Opial’s condition if, for any sequence in E, implies that for all with . It is well known that every Hilbert space satisfies Opial’s condition.
A mapping T with domain and range in E is said to be demiclosed at p if whenever is a sequence in such that converges weakly to and converges strongly to p, then .
T is said to be semi-compact if for any bounded sequence with , there exists a subsequence of such that converges strongly to a point .
Recently, Zhao and Chang [16] proposed the following algorithm for solving k-strictly pseudononspreading mappings and equilibrium problem in Hilbert spaces.
where , . Under some suitable conditions, they proved that the sequences , weakly and strongly converge to a solution of the problem .
For finding a split feasibility problem for k-strictly pseudononspreading mappings in a Hilbert space, in [17], Quan and Chang presented the following iterative method:
where γ is a constant and , λ is the spectral of the operator , , and is a sequence in with . Under some suitable conditions, they proved that weakly and strongly converges to a split fixed point .
Inspired and motivated by the recent works of Zhao and Chang [16], Quan and Chang [17], etc., in this paper, we propose an iterative scheme to approximate a common element of the set of solutions of k-asymptotically strictly pseudononspreading mappings and mixed equilibrium problem in infinite-dimensional Hilbert spaces. Some weak and strong convergence theorems are proved. At the same time, the demiclosed principle of a k-asymptotically strictly pseudononspreading mapping is shown. The results presented in this paper improve and extend some recent corresponding results.
2 Preliminaries
Throughout this paper, we denote the strong convergence and weak convergence of a sequence to a point by , , respectively.
Let H be a Hilbert space with the inner product and the norm , let C be a nonempty closed convex subset of H. For every point , there exists a unique nearest point of C, denoted by , such that for all . Such a is called the metric projection from H onto C. It is well known that is a firmly nonexpansive mapping from H to C, i.e.,
Further, for any and , if and only if
For solving mixed equilibrium problems, we assume that the bifunction satisfies the following conditions:
(A1) , ;
(A2) , ;
(A3) For all , ;
(A4) For each , the function is convex and lower semi-continuous.
Lemma 2.1 [18]
Let C be a nonempty closed convex subset of a Hilbert space H. Let F be a bifunction from to R satisfying (A1)-(A4), and let be a proper lower semi-continuous and convex function such that . For and , define a mapping as follows:
Then
-
(1)
For each , ;
-
(2)
is single-valued;
-
(3)
is firmly nonexpansive, that is, ,
-
(4)
;
-
(5)
is closed and convex.
Lemma 2.2 [13]
Let H be a real Hilbert space. Then the following results hold:
-
(i)
For all and for all ,
-
(ii)
.
-
(iii)
If is a sequence in H which converges weakly to , then
The demiclosed principle and the closeness and convexity of the set of fixed points of a nonlinear mapping play very important roles in investigating many nonlinear problems. We now show the demiclosed principle of k-asymptotically strictly pseudononspreading mapping and the closeness and convexity of the set of fixed points of such a mapping, respectively.
Lemma 2.3 Let C be a nonempty closed convex subset of a real Hilbert space H and let be a continuous k-asymptotically strictly pseudononspreading mapping. If , then it is closed and convex.
Proof Let be a sequence which converges to , we show that .
Since T is k-asymptotically strictly pseudononspreading, we have
Using (2.4) in (2.3), we obtain
so
Since and as , we get that . Since T is continuous, which implies that . Hence, .
Now, we show that is convex.
For and , put . We show that . In fact, we have
So,
Since as , we obtain that , which implies that , . Hence, , which means that is convex. □
Lemma 2.4 Let C be a nonempty closed convex subset of a real Hilbert space H, and let be a k-asymptotically strictly pseudononspreading and uniformly L-Lipschitzian mapping. Then, for any sequence in C converging weakly to a point p and converging strongly to 0, we have .
Proof Since , by induction we can prove that
In fact, it is obvious that the conclusion is true for . Suppose that the conclusion holds for , now we prove that the conclusion is also true for .
Indeed, since T is uniformly L-Lipschitzian, we have
So, .
For each , define by
Then from Lemma 2.2 we have
Thus, for any , and
It follows from (2.7) and (2.8) that
That is,
Hence we have
This is , as desired. The proof is completed. □
Lemma 2.5 [19]
Let the number sequences and satisfy
where , and . Then
-
(1)
exists;
-
(2)
if , then .
3 Main results
Theorem 3.1 Let C be a nonempty and closed convex subset of a real Hilbert space H, let F be a bifunction from to R satisfying (A1)-(A4), and let be a proper lower semi-continuous and convex function such that . Let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , . Let be a sequence generated by
where is a sequence in with , is a sequence in with , , and the sequence satisfies that and . If , then the sequence converges weakly to a point .
Proof The proof is divided into four steps.
Step 1. Firstly, we prove that exists for any .
Taking and putting , it follows from Lemma 2.1 that , , we have
Since
and
from (3.4) and (3.5) we have
Substituting (3.6) into (3.3) and simplifying, we have
On the other hand,
Since is a -asymptotically strictly pseudononspreading mapping, we have
Again since
so we have
From (3.8) and (3.11), we have
By using (3.7) and (3.12), we have
Let . Since and , so , we have
Using Lemma 2.5, we show that exists. Further, it follows from (3.2) and (3.12) that and are bounded.
On the other hand, from (3.14) we have
Since exists and by the fact that , taking limit on both sides of inequality (3.15), we get
Step 2. Now, we prove that , and .
It follows from Lemma 2.1 that , , so
This shows that
By (3.13) and (3.19), we obtain
So,
Thus, we obtain
In fact, it follows from (3.1) that
From (3.16), (3.17) and (3.22) we have
Similarly, it follows from (3.1) that
where
On the other hand, it follows from Lemma 2.1 that and . We have
and
Particularly, we have
and
Summing up (3.27) and (3.28) and using (A2), we obtain
Thus,
which implies that
Therefore,
Thus, we have
It follows from (3.16), (3.17), (3.24), (3.25) and (3.29) that
and
Put . Since
from (3.16), (3.22), (3.30) and (3.32) we get
Similarly, we have
This implies that
Since , so
By (3.24) and (3.35), we have
It follows from (3.22) and (3.36) that
Since exists for any and , it follows from (3.36) that holds. Similarly, holds for any .
Step 3. We show that .
Firstly, we show that .
In fact, since is bounded, there exists a subsequence such that . Hence, for any positive integer , there exists a subsequence with such that . Again, by (3.34) we know that as , therefore we have that .
Since is demiclosed at zero, it follows from Lemma 2.4 that . By the arbitrariness of , we have
On the other hand, since , we know that , too. Similarly, it follows from (3.33) and Lemma 2.4 that . By the arbitrariness of , we have
Now, we show that .
By Lemma 2.1, since , we have
From (A2), we obtain
and hence
By , we have . Since , it follows from (A4) and the weak lower semicontinuity of φ that
Put for all and . Consequently, we get . Hence
From (A1) and (A4), and the convexity of φ, we have
Therefore
Letting , and from the weak lower semicontinuity of φ, we have
This implies that . Hence .
Step 4. Finally, we prove that and , .
Due to , we know that from (3.37). Suppose that there exists another subsequence of such that with . Using the same proof method as in Step 3, we know that . Consequently, exists. By using Opial’s property of a Hilbert space, we have
This is a contradiction. Therefore . By (3.1) and (3.22), we have . Therefore, the conclusion follows.
This completes the proof of Theorem 3.1. □
Taking , in Theorem 3.1, we have the following result.
Corollary 3.2 Let C be a nonempty and closed convex subset of a real Hilbert space H, let F be a bifunction from to R satisfying (A1)-(A4), and let be a uniformly L-Lipschitzian and k-asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and ρ-asymptotically strictly pseudononspreading mapping with the sequence such that . Let be a sequence generated by
where , , is a sequence in with , is a sequence in with and the sequence with and . If , then the sequence converges weakly to a point .
Corollary 3.3 Let C be a nonempty and closed convex subset of a real Hilbert space H, let F be a bifunction from to R satisfying (A1)-(A4), and let be a proper lower semi-continuous and convex function such that . Let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , . Let be a sequence generated by
where , , is a sequence in with , is a sequence in with and the sequence with and . If , and there exists a positive integer j such that is semi-compact, then the sequence converges strongly to a point .
Proof Without loss of generality, we can assume that is semi-compact. It follows from (3.34) that
Therefore, there exists a subsequence of (for the sake of convenience we still denote it by ) such that . Since , , and so . By virtue of the fact that exists, we know that
That is, , and converge strongly to the point . This completes the proof. □
4 Applications
4.1 Application to a convex minimization problem
It is well known that mixed equilibrium problem (1.2) reduces to the convex minimization problem as . Therefore, Theorem 3.1 can be used to solve convex minimization problem (1.3), and the following result can be directly deduced from Theorem 3.1.
Theorem 4.1 Let C be a nonempty and closed convex subset of a real Hilbert space H, let be a proper lower semi-continuous and convex function such that . Let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , . Let be a sequence generated by
where , , is a sequence in with , is a sequence in with , and the sequence with and . If , then the sequence converges weakly to a point .
4.2 Application to a convex feasibility problem
The so-called convex feasibility problem for a family of mappings (where ω may be a finite positive integer or +∞) is to find a point of the nonempty intersection , where is the fixed point set of mapping , .
In Theorem 3.1 if , , then the condition ‘ such that , ’ is equivalent to . Therefore, the following result can be directly obtained from Theorem 3.1.
Theorem 4.2 Let C be a nonempty and closed convex subset of a real Hilbert space H, let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , . Let be a sequence generated by
where is a sequence in with and is a sequence in with , . If , then the sequence converges weakly to a point , which is a solution of the convex feasibility problem for mappings and .
4.3 Application to the mixed variational inequality problem of Browder type
A variational inequality problem (VIP) is formulated as a problem of finding a point with property , , . We will denote the solution set of VIP by . We know that given a mapping , let for all . Then if and only if is a solution of the variational inequality for all , i.e., is a solution of the variational inequality.
In [20], the mixed variational inequality of Browder type (VI) is shown to be equivalent to finding a point such that
We will denote the solution set of a mixed variational inequality of Browder type by .
A mapping is said to be an α-inverse-strongly monotone mapping if there exists a constant such that for any . Setting , it is easy to show that F satisfies conditions (A1)-(A4) as A is an α-inverse-strongly monotone mapping. Then it follows from Theorem 3.1 that the following result holds.
Theorem 4.3 Let C be a nonempty and closed convex subset of a real Hilbert space H, let be an α-inverse-strongly monotone mapping, and let be a proper lower semi-continuous and convex function such that . Let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , let be a uniformly -Lipschitzian and -asymptotically strictly pseudononspreading mapping with the sequence such that , . Let be a sequence generated by
where is a sequence in with , is a sequence in with , , and the sequence satisfies and . If , then the sequence converges weakly to a point .
References
Blum E, Oettli W: From optimization and variational inequalities to equilibrium problems. Math. Stud. 1994, 63: 123–145.
Noor M, Oettli W: On general nonlinear complementarity problems and quasi-equilibria. Matematiche 1994, 49: 313–346.
Jaiboon C, Kumam P: A hybrid extragradient viscosity approximation method for solving equilibrium problems and fixed point problems of infinitely many nonexpansive mappings. Fixed Point Theory Appl. 2009., 2009: Article ID 374815
Chang SS, Chan CK, Joseph Lee HW: Modified block iterative algorithm for quasi- ϕ -asymptotically nonexpansive mappings and equilibrium problem in Banach spaces. Appl. Math. Comput. 2011, 217: 7520–7530. 10.1016/j.amc.2011.02.060
Moudafi A, Thera M Lecture Notes in Economics and Mathematical Systems 477. In Proximal and Dynamical Approaches to Equilibrium Problems. Springer, Berlin; 1999:187–201.
Peng JW, Yao JC: A viscosity approximation scheme for system of equilibrium problems, nonexpansive mappings and monotone mappings. Nonlinear Anal. 2009, 71: 6001–6010. 10.1016/j.na.2009.05.028
Chang SS, Chan CK, Joseph Lee HW, Yang L: A system of mixed equilibrium problems, fixed point problems of strictly pseudo-contractive mappings and nonexpansive semi-groups. Appl. Math. Comput. 2010, 216: 51–60. 10.1016/j.amc.2009.12.060
Kumam P, Jaiboon C: A new hybrid iterative method for mixed equilibrium problems and variational inequality problem for relaxed cocoercive mappings with application to optimization problems. Nonlinear Anal. Hybrid Syst. 2009, 3(4):510–530. 10.1016/j.nahs.2009.04.001
Kohsaka F, Takahashi W: Fixed point theorems for a class of nonlinear mappings relate to maximal monotone operators in Banach spaces. Arch. Math. 2008, 91: 166–177. 10.1007/s00013-008-2545-8
Kohsaka F, Takahashi W: Existence and approximation of fixed points of firmly nonexpansive-type mappings in Banach spaces. SIAM J. Optim. 2008, 19: 824–835. 10.1137/070688717
Iemoto S, Takahashi W: Approximating common fixed points of nonexpansive mappings and nonspreading mappings in a Hilbert space. Nonlinear Anal. 2009, 71: 2080–2089.
Browder FE, Petryshyn WV: Construction of fixed points of nonlinear mappings in Hilbert spaces. J. Math. Anal. Appl. 1967, 20: 197–228. 10.1016/0022-247X(67)90085-6
Osilike MO, Isiogugu FO: Weak and strong convergence theorems for nonspreading type mappings in Hilbert spaces. Nonlinear Anal. 2011, 74: 1814–1822. 10.1016/j.na.2010.10.054
Kurokawa Y, Takahashi W: Weak and strong convergence theorems for nonspreading mappings in Hilbert spaces. Nonlinear Anal. 2010, 73: 1562–1568. 10.1016/j.na.2010.04.060
Chang SS, Cho YJ, Kim JK, Zhang WB, Yang L: Multiple-set split feasibility problems for asymptotically strict pseudocontractions. Abstr. Appl. Anal. 2012., 2012: Article ID 491760 10.1155/2012/491760
Zhao YH, Chang SS: Weak and strong convergence theorems for strictly pseudononspreading mappings and equilibrium problem in Hilbert spaces. Abstr. Appl. Anal. 2013., 2013: Article ID 169206 10.1155/2013/169206
Quan J, Chang SS, Zhang X: Multiple-set split feasibility problems for k -strictly pseudononspreading mapping in Hilbert spaces. Abstr. Appl. Anal. 2013., 2013: Article ID 342545 10.1155/2013/342545
Peng JW, Liou YC, Yao JC: An iterative algorithm combining viscosity method with parallel method for a generalized equilibrium problem and strict pseudocontractions. Fixed Point Theory Appl. 2009., 2009: Article ID 794178 10.1155/2009/794178
Tan KK, Xu HK: Approximating fixed points of nonexpansive mappings by the Ishikawa iteration process. J. Math. Anal. Appl. 1993, 178: 301–308. 10.1006/jmaa.1993.1309
Alber YI: Metric and generalized projection operators in Banach space: properties and application. In Theory and Applications of Nonlinear Operators of Accretive and Monotone Type. Edited by: Kartosator AG. Dekker, New York; 1996:15–50.
Acknowledgements
The authors would like to express their thanks to the reviewers and editors for their helpful suggestions and advice. This work was supported by the National Natural Science Foundation of China (Grant No. 11361070).
Author information
Authors and Affiliations
Corresponding author
Additional information
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Both authors contributed equally to this work. Both authors read and approved the final manuscript.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
About this article
Cite this article
Ma, Z., Wang, L. Demiclosed principle and convergence theorems for asymptotically strictly pseudononspreading mappings and mixed equilibrium problems. Fixed Point Theory Appl 2014, 104 (2014). https://doi.org/10.1186/1687-1812-2014-104
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/1687-1812-2014-104