Abstract
In this paper, we introduce and study iterative algorithms for solving split mixed equilibrium problems and fixed point problems of λ-hybrid multivalued mappings in real Hilbert spaces and prove that the proposed iterative algorithm converges weakly to a common solution of the considered problems. We also provide an example to illustrate the convergence behavior of the proposed iteration process.
Keywords: split mixed equilibrium problems, hybrid multivalued mappings, weak convergence, Hilbert spaces
Introduction
Let H be a real Hilbert space with inner product and induced norm . Let C be a nonempty closed convex subset of H, be a function, and be a bifunction. The mixed equilibrium problem is to find such that
| 1.1 |
The solution set of mixed equilibrium problem is denoted by . In particular, if , this problem reduces to the equilibrium problem, which is to find such that . The solution set of equilibrium problem is denoted by EP(F).
The mixed equilibrium problem is very general in the sense that it includes, as special cases, optimization problems, variational inequality problems, minimization problems, fixed point problems, Nash equilibrium problems in noncooperative games, and others; see, e.g., [1–4].
In 1994, Censor and Elfving [5] firstly introduced the following split feasibility problem in finite-dimensional Hilbert spaces: Let , be two Hilbert spaces and C, Q be nonempty closed convex subsets of and , respectively, and let be a bounded linear operator. The split feasibility problem is formulated as finding a point with the property
The split feasibility problem can extensively be applied in fields such as intensity-modulated radiation therapy, signal processing and image reconstruction, then the split feasibility problem has received so much attention by so many scholars; see [6–9].
In 2013, Kazmi and Rizvi [10] introduced and studied the following split equilibrium problem: let and . Let and be nonlinear bifunctions and let be a bounded linear operator. The split equilibrium problem is to find such that
| 1.2 |
The solution set of the split equilibrium problem is denoted by
The authors gave an iterative algorithm to find the common element of sets of solution of the split equilibrium problem and hierarchical fixed point problem; for more details refer to [11, 12].
In 2016, Suantai et al. [13] proposed the iterative algorithm to solve the problems for finding a common elements the set of solution of the split equilibrium problem and the fixed point of a nonspreading multivalued mapping in Hilbert space, given sequence by
| 1.3 |
where , and such that L is the spectral radius of and is the adjoint of A, , , is a -nonspreading multivalued mapping, and are two bifunctions. The authors showed that under certain conditions, the sequence converges weakly to an element of .
Several iterative algorithms have been developed for solving split feasibility problems and related split equilibrium problems; see, e.g., [14–16].
Motivated and inspired by the above results and related literature, we propose an iterative algorithm for finding a common element of the set of solutions of split mixed equilibrium problems and the set of fixed points of λ-hybrid multivalued mappings in real Hilbert spaces. Then we prove some weak convergence theorems which extend and improve the corresponding results of Kazmi and Rizvi [10] and Suantai et al. [13] and many others. We finally provide numerical examples for supporting our main result.
Preliminaries
Let C be a nonempty closed convex subset of a real Hilbert space H. We denote the strong convergence and the weak convergence of the sequence to a point by and , respectively. It is also well known [17] that a Hilbert space H satisfies Opial’s condition, that is, for any sequence with , the inequality
holds for every with .
The following two lemmas are useful for our main results.
Lemma 2.1
In a real Hilbert space H, the following inequalities hold:
;
;
;
- If is a sequence in H which converges weakly to , then
Lemma 2.2
[18]
Let H be a Hilbert space and be a sequence in H. Let be such that and exist. If and are subsequences of which converge weakly to u and v, respectively, then .
A single-valued mapping is called δ-inverse strongly monotone [19] if there exists a positive real number δ such that
For each , we see that is a nonexpansive single-valued mapping, that is,
We denote by and the collection of all nonempty closed bounded subsets and nonempty compact subsets of C, respectively. The Hausdorff metric on is defined by
where is the distance from a point x to a subset B. Let be a multivalued mapping. An element is called a fixed point of S if . The set of all fixed points of S is denoted by , that is, . Recall that a multivalued mapping is called
-
(i)nonexpansive if
-
(ii)quasi-nonexpansive if and
-
(iii)nonspreading [13] if
-
(iv)λ-hybrid [20] if there exists such that
We note that 0-hybrid is nonexpansive, 1-hybrid is nonspreading, and if S is λ-hybrid with , then S is quasi-nonexpansive. It is well known [20] that if S is λ-hybrid, then is closed. In addition, if S satisfies the condition: for all , then is also convex.
The following result is a demiclosedness principle for λ-hybrid multivalued mapping in a real Hilbert space.
Lemma 2.3
[20]
Let C be a nonempty closed convex subset of a real Hilbert space H and be a λ-hybrid multivalued mapping. If is a sequence in C such that and with , then .
For solving the mixed equilibrium problem, we assume that the bifunction satisfies the following assumption:
Assumption 2.4
Let C be a nonempty closed and convex subset of a Hilbert space . Let be the bifunction, is convex and lower semicontinuous satisfies the following conditions:
for all ;
is monotone, i.e., ;
for each , ;
for each , is convex and lower semicontinuous;
- for each and fixed , there exist a bounded subset and such that, for any ,
C is a bounded set.
Lemma 2.5
[21]
Let C be a nonempty closed and convex subset of a Hilbert space . Let be a bifunction satisfies Assumption 2.4 and let be a proper lower semicontinuous and convex function such that . For and . Define a mapping as follows:
for all . Assume that either (B1) or (B2) holds. Then the following conclusions hold:
for each , ;
is single-valued;
- is firmly nonexpansive, i.e., for any ,
;
is closed and convex.
Further, assume that satisfying Assumption 2.4 and is a proper lower semicontinuous and convex function such that , where Q is a nonempty closed and convex subset of a Hilbert space . For each and , define a mapping as follows:
Then we have the following:
-
(6)
for each , ;
-
(7)
is single-valued;
-
(8)
is firmly nonexpansive;
-
(9)
;
-
(10)
is closed and convex.
Main results
In this section, we prove the weak convergence theorems for finding a common element of the set of solutions of split mixed equilibrium problems and the set of fixed points of λ-hybrid multivalued mappings in real Hilbert spaces and give a numerical example to support our main result.
We introduce the definition of split mixed equilibrium problems in real Hilbert spaces as follows.
Definition 3.1
Let C be a nonempty closed convex subset of a real Hilbert space and Q be a nonempty closed convex subset of a real Hilbert space . Let and be nonlinear bifunctions, let and be proper lower semicontinuous and convex functions such that and , and let be a bounded linear operator. The split mixed equilibrium problem is to find such that
| 3.1 |
and such that
| 3.2 |
The solution set of the split mixed equilibrium problem (3.1) and (3.2) is denoted by
We now get our main result.
Theorem 3.2
Let C be a nonempty closed convex subset of a real Hilbert space and Q be a nonempty closed convex subset of a real Hilbert space . Let be a bounded linear operator and a λ-hybrid multivalued mapping. Let , be bifunctions satisfying Assumption 2.4, let and be a proper lower semicontinuous and convex functions such that and , respectively, and is upper semicontinuous in the first argument. Assume that and for all . Let be a sequence generated by and
| 3.3 |
where , , , and such that L is the spectral radius of and is the adjoint of A. Assume that the following conditions hold:
;
;
.
Then the sequence generated by (3.3) converges weakly to .
Proof
First, we show that is a -inverse strongly monotone mapping. Since is firmly nonexpansive and is 1-inverse strongly monotone, we see that
for all . This implies that is a -inverse strongly monotone mapping. Since , it follows that is a nonexpansive mapping.
Now, we divide the proof into five steps as follows:
Step 1. Show that is bounded.
Let . Then we have and . By nonexpansiveness of , it implies that
| 3.4 |
This implies that
| 3.5 |
and so
| 3.6 |
It follows that
| 3.7 |
| 3.8 |
This implies that is decreasing and bounded below, thus exists for all .
Step 2. Show that .
From Lemma 2.1(3), (3.5), (3.7), and , we have
| 3.9 |
This implies that
From Condition (C1) and exists, we have
| 3.10 |
Step 3. Show that and .
For , we see that
Thus, by (3.5) and (3.7), we have
| 3.11 |
Therefore, we have
Since , it follows by Condition (C1) and the existence of that
| 3.12 |
Since is firmly nonexpansive and is nonexpansive, we have
which implies that
| 3.13 |
This implies by (3.5) and (3.7) that
Therefore, we have
where . This implies by Condition (C1), (3.12), and the existence of that
| 3.14 |
From (3.5), (3.7), and the definition of , we obtain
This implies that
From Conditions (C1), (C2), and the existence of , we have
| 3.15 |
| 3.16 |
Step 4. Show that , where . Since is bounded and is reflexive, is nonempty. Let be an arbitrary element. Then there exists a subsequence converging weakly to p. From (3.14), it implies that as . By (3.16) and Lemma 2.3, we have .
Next, we show that . Since , we have
which implies that
From Assumption 2.4(A2), we have
and hence
This implies by , Condition (C3), (3.12), (3.14), Assumption 2.4(A2), and the proper lower semicontinuity of φ that
Put for all and . Consequently, we get and hence . So, by Assumption 2.4(A1)-(A4), we have
Hence, we have
Letting , by Assumption 2.4(A3) and the proper lower semicontinuity of φ, we have
This implies that .
Since A is a bounded linear operator, we have . Then it follows from (3.12) that
| 3.17 |
By the definition of , we have
Since is upper semicontinuous in the first argument, it implies by (3.17) that
This shows that . Therefore, and hence .
Step 5. Show that converges weakly to an element of Θ. It is sufficient to show that is a singleton set. Let and , be two subsequences of such that and . From (3.14), we also have and . By (3.16) and Lemma 2.3, we see that . Applying Lemma 2.2, we obtain . This completes the proof. □
If in (3.1) and (3.2), then the split mixed equilibrium problem reduces to split equilibrium problem. So, the following result can be obtained from Theorem 3.2 immediately.
Theorem 3.3
Let C be a nonempty closed convex subset of a real Hilbert space and Q be a nonempty closed convex subset of a real Hilbert space . Let be a bounded linear operator and a λ-hybrid multivalued mapping. Let , be bifunctions satisfying Assumption 2.4, and is upper semicontinuous in the first argument. Assume that and for all . Let be a sequence generated by and
| 3.18 |
where , , , and such that L is the spectral radius of and is the adjoint of A. Assume that the following conditions hold:
;
;
.
Then the sequence generated by (3.18) converges weakly to .
Remark 3.4
-
(i)
Theorems 3.2 and 3.3 extend the corresponding one of Suantai et al. [13] and Kazmi and Rizvi [10] to λ-hybrid multivalued mapping and to a split mixed equilibrium problem. In fact, we present a new iterative algorithm for finding a common element of the set of solutions of split mixed equilibrium problems and the set of fixed points of λ-hybrid multivalued mappings in a real Hilbert space.
-
(ii)
It is well known that the class of λ-hybrid multivalued mappings contains the classes of nonexpansive multivalued mappings, nonspreading multivalued mappings. Thus, Theorems 3.2 and 3.3 can be applied to these classes of mappings.
We give an example to illustrate Theorem 3.2 as follows.
Example 3.5
Let , , , and . Let defined by for each . Then for each . So, is the spectral radius of . Define a multivalued mapping by
It easy to see that S is 1-hybrid multivalued mapping with and . For each , define the bifunction by and define for each . For each , define the bifunction by and define for each .
Choose , , , and . It is easy to check that , , , , satisfy all conditions in Theorem 3.2.
For each , we compute . Find z such that
for all . Thus, by Lemma 2.5(2), it follows that . That is, for each . Furthermore, we get
Next, we find such that for all , where . Note that
Thus, by Lemma 2.5(2), it follows that
Then the algorithm (3.3) becomes
| 3.19 |
where
We choose if and if . By using SciLab, we compute the iterates of (3.19) for the initial point . The numerical experiment’s results of our iteration for approximating the point 0 are given in Table 1.
Table 1.
| n | ||
|---|---|---|
| 1 | −3.0000000e + 00 | - |
| 2 | −6.8786127e − 02 | 2.9312139e + 00 |
| 3 | 0.0000000e + 00 | 6.8786127e − 02 |
| 4 | 0.0000000e + 00 | 0.0000000e + 00 |
Conclusions
The results presented in this paper extend and generalize the work of Suantai et al. [13] and Kazmi and Rizvi [10]. The main aim of this paper is to propose an iterative algorithm to find an element for solving a class of split mixed equilibrium problems and fixed point problems for λ-hybrid multivalued mappings under weaker conditions. Some sufficient conditions for the weak convergence of such proposed algorithm are given. Also, in order to show the significance of the considered problem, some important applications are discussed.
Acknowledgements
The authors are thankful to the referees for careful reading and the useful comments and suggestions.
Footnotes
Funding
This work was supported by the Research Center for Pure and Applied Mathematics, Research and Development Institute, Nakhon Pathom Rajabhat University, Nakhon Pathom, Thailand. The second author was also supported by the Thailand Research Fund under the project RTA5780007.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
All authors contributed equally and significantly in writing this paper. All authors read and approved the final manuscript.
Publisher’s Note
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Contributor Information
Nawitcha Onjai-uea, Email: nawitcha@hotmail.com.
Withun Phuengrattana, Email: withun_ph@yahoo.com.
References
- 1.Ceng LC, Yao JC. A hybrid iterative scheme for mixed equilibrium problems and fixed point problems. J. Comput. Appl. Math. 2008;214:186–201. doi: 10.1016/j.cam.2007.02.022. [DOI] [Google Scholar]
- 2.Blum E, Oettli W. From optimization and variational inequalities to equilibrium problems. Math. Stud. 1994;63:123–145. [Google Scholar]
- 3.Combettes PI, Hirstoaga SA. Equilibrium programming in Hilbert spaces. J. Nonlinear Convex Anal. 2005;6:117–136. [Google Scholar]
- 4.Flam SD, Antipin AS. Equilibrium programming using proximal-like algorithm. Math. Program. 1997;78:29–41. doi: 10.1007/BF02614504. [DOI] [Google Scholar]
- 5.Censor Y, Elfving T. A multiprojection algorithm using Bregman projections in a product space. Numer. Algorithms. 1994;8:221–239. doi: 10.1007/BF02142692. [DOI] [Google Scholar]
- 6.Censor Y, Bortfeld T, Martin B, Trofimov A. A unified approach for inversion problems in intensity-modulated radiation therapy. Phys. Med. Biol. 2006;51:2353–2365. doi: 10.1088/0031-9155/51/10/001. [DOI] [PubMed] [Google Scholar]
- 7.Censor Y, Elfving T, Kopf N, Bortfeld T. The multiple-sets split feasibility problem and its applications for inverse problems. Inverse Probl. 2005;21:2071–2084. doi: 10.1088/0266-5611/21/6/017. [DOI] [Google Scholar]
- 8.Censor Y, Motova A, Segal A. Perturbed projections and subgradient projections for the multiple-sets split feasibility problem. J. Math. Anal. Appl. 2007;327:1244–1256. doi: 10.1016/j.jmaa.2006.05.010. [DOI] [Google Scholar]
- 9.Chan T, Shen J. Image Processing and Analysis: Variational, PDE, Wavelet, and Stochastic Methods. Philadelphia: SIAM; 2005. [Google Scholar]
- 10.Kazmi KR, Rizvi SH. Iterative approximation of a common solution of a split equilibrium problem, a variational inequality problem and a fixed point problem. J. Egypt. Math. Soc. 2013;21:44–51. doi: 10.1016/j.joems.2012.10.009. [DOI] [Google Scholar]
- 11.Bnouhachem A. Algorithms of common solutions for a variational inequality, a split equilibrium problem and a hierarchical fixed point problem. Fixed Point Theory Appl. 2013;2013 doi: 10.1186/1687-1812-2013-278. [DOI] [Google Scholar]
- 12.Bnouhachem A. Strong convergence algorithm for split equilibrium problems and hierarchical fixed point problems. Sci. World J. 2014;2014 doi: 10.1155/2014/390956. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 13.Suantai S, Cholamjiak P, Cho YJ, Cholamjiak W. On solving split equilibrium problems and fixed point problems of nonspreading multi-valued mappings in Hilbert spaces. Fixed Point Theory Appl. 2016;2016 doi: 10.1186/s13663-016-0509-4. [DOI] [Google Scholar]
- 14.Deepho J, Kumam W, Kumam P. A new hybrid projection algorithm for solving the split generalized equilibrium problems and the system of variational inequality problems. J. Math. Model. Algorithms Oper. Res. 2014;13(4):405–423. doi: 10.1007/s10852-014-9261-0. [DOI] [Google Scholar]
- 15.Kumam W, Deepho J, Kumam P. Hybrid extragradient method for finding a common solution of the split feasibility and system of equilibrium problems. Dyn. Contin. Discrete Impuls. Syst., Ser. B, Appl. Algorithms. 2014;21(6):367–388. [Google Scholar]
- 16.Deepho J, Martinez-Moreno J, Kumam P. A viscosity of Cesaro mean approximation method for split generalized equilibrium, variational inequality and fixed point problems. J. Nonlinear Sci. Appl. 2016;9:1475–1496. [Google Scholar]
- 17.Opial Z. Weak convergence of the sequence of successive approximation for nonexpansive mappings. Bull. Am. Math. Soc. 1967;73:591–597. doi: 10.1090/S0002-9904-1967-11761-0. [DOI] [Google Scholar]
- 18.Suantai S. Weak and strong convergence criteria of Noor iterations for asymptotically nonexpansive mappings. J. Math. Anal. Appl. 2005;311:506–517. doi: 10.1016/j.jmaa.2005.03.002. [DOI] [Google Scholar]
- 19.Iiduka H, Takahashi W. Weak convergence theorem by Cesaro means for nonexpansive mappings and inverse-strongly monotone mappings. J. Nonlinear Convex Anal. 2006;7:105–113. [Google Scholar]
- 20.Suantai S, Phuengrattana W. Existence and convergence theorems for λ-hybrid mappings in Hilbert spaces. Dyn. Contin. Discrete Impuls. Syst. Ser. A, Math. Anal. 2015;22:177–188. [Google Scholar]
- 21.Ma Z, Wang L, Chang SS, Duan W. Convergence theorems for split equality mixed equilibrium problems with applications. Fixed Point Theory Appl. 2015;2015 doi: 10.1186/s13663-015-0281-x. [DOI] [Google Scholar]
