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Existence and convergence theorems for the new system of generalized mixed variational inequalities in Banach spaces
Journal of Inequalities and Applications volume 2012, Article number: 9 (2012)
Abstract
In this article, we introduce and consider the three-step iterative algorithms for solving a new system of generalized mixed variational inequalities involving different three multi-valued operators. In this study, we use a generalized f-projection method for finding the solutions of generalized system of mixed variational inequalities in Banach spaces. Our result in this article improves and generalizes some known corresponding results in the literature.
2000 Mathematics Subject Classification: 47H10; 47H19; 49J40.
1. Introduction
Let B be a real Banach space which dual space B* and C be a nonempty closed convex subset of B. Let 〈·, ·〉 be the dual pair between B and B*, J denotes the normalized duality mapping and ℝ be the field of real numbers. Let be nonlinear operators. Let f1, f2, f3: B → (-∞, +∞] be three mappings. We consider the following problem:
Find x*, y*, z* ∈ C ⊂ B such that there exist u* ∈ T1(y*), v* ∈ T2(z*), and w* ∈ T3(x*) satisfying
The problem (★) is called the system of generalized mixed variational inequality problems, the solution of (★) is denoted by (SGMVIP).
Some special cases of the problem (★):
-
(I)
If f 1(x) = f 2(x) = f 3(x) = 0, ∀x ∈ C, then problem (★) is equivalent to find x*, y*, z* ∈ C such that
(1.1)
The problem (1.1) is called the system of generalized variational inequality problems, the solution of (1.1) is denoted by (SGVIP).
-
(II)
If x* = z*, T 3(y) = 0, and f 3(x) = 0, ∀x, y ∈ C, then problem (★) is equivalent to the two step of the system of generalized mixed variational inequality problems: Find x*, y* ∈ C ⊂ B such that there exist u* ∈ T 1(y*) and v* ∈ T 2(x*) satisfying
(1.2)
which was studied by Zhang and Deng [1].
-
(III)
If T = T 1 = T 2 = T 3, f 2(x) = f 3(x) = 0, ∀x ∈ C and x* = y* = z*, then problem (★) is equivalent to the generalized variational inequality problem associated with C, T, and f denoted by GVI(C, T, f): find x* ∈ C such that there exist u* ∈ T(x*) satisfying
(1.3)
which was studied by Fan et al. [2].
If f1(x) = 0, ∀x ∈ C and T is single-valued, then problem (1.3) reduces to the classical variational inequality problem, which consists in finding x ∈ C such that
which is known as the classical variational inequality introduced and studied by Stampacchia [3] in 1964. For the recent applications, numerical methods and formulations, (see for example [3–10]) and the references therein. The variational inequalities are equivalent to the fixed point problems. In particular, the solution of the variational inequalities can be computed using the iterative projection method. Alber [11] presented some applications of the generalized projections to approximately solving variational inequalities and von Neumann intersection problem in Banach spaces. In 2005, Li [12] extended the generalized projection operator from uniformly convex and uniformly smooth Banach spaces to reflexive Banach spaces and studied some properties of the generalized projection operator with applications to solving the variational inequality in Banach spaces.
In 2007, Wu and Huang [13], they proved some properties of the generalized f-projection operator and proposed iterative method of approximating solutions for a class of generalized variational inequalities in Banach spaces. In 2009, Fan et al. [2] presented some basic results for the generalized f-projection operator and discussed the existence of solutions and approximation of the solutions for generalized variational inequalities in noncompact subsets of Banach spaces. In 2010, Petrot [8] used the resolvent operator technique to find the common solutions for a generalized system of relaxed cocoercive mixed variational inequality problems and fixed point problems for Lipschitz mappings in Hilbert spaces.
In 2011, Zhang and Deng [1] introduced and considered the system of mixed variational inequalities in Banach spaces. Using the generalized f-projection operator technique, they introduced two-step iterative methods for solving the system of mixed variational inequalities and proved the convergence of the proposed iterative methods under suitable conditions in Banach spaces.
Noor [4] suggested and analyzed several three-step iterative methods, which are also known as Noor iterations, for solving variational inequalities. It has been shown that three-step iterative methods are more efficient than two-step and one-step iterative methods. In addition, it is known that the convergence analysis of three-step can be proved under much weaker conditions.
Motivated and inspired by the recent research studies in this fascinating area, the purpose of this article is to introduce and analyze three-step iterative algorithm for finding a new system of generalized mixed variational inequality problems with three difference multi-valued operators in Banach spaces. Using the generalized f-projection method. The results presented in this article extend and improve the results of Zhang and Deng [1] and Fan et al. [2] and some authors.
2. Preliminaries
A Banach space B is said to be strictly convex if for all x, y ∈ B with ||x|| = ||y|| = 1 and x ≠ y. Let U = {x ∈ B: ||x|| = 1} be the unit sphere of B. then a Banach space B is said to be smooth if the exists for each x, y ∈ U. It is also said to be uniformly smooth if the limit exists uniformly in x, y ∈ U. Let B be a Banach space. The modulus of smoothness of B is the function ρ B : [0, ∞) → [0, ∞) defined by . The modulus of convexity of B is the function η B : [0, 2] → [0, 1] defined by . The normalized duality mapping is defined by J(x) = {x* ∈ B*: 〈x, x*〉 = ||x||2, ||x*|| = ||x||}. If B is a Hilbert space, then J = I, where I is the identity mapping.
If B is a reflexive smooth and strictly convex Banach space and J*: B* → 2Bis the normalized duality mapping on B*, then and J*J = I B , where I B and are the identity mappings on B and B*. If B is a uniformly smooth and uniformly convex Banach space, then J is uniformly norm-to-norm continuous on bounded subsets of B and J* is also uniformly norm-to-norm continuous on bounded subsets of B*.
Let B and F be Banach spaces, T: D(T) ⊂ B → F, the operator T is said to be compact if it is continuous and maps the bounded subsets of D(T) onto the relatively compact subsets of F; the operator T is said to be weak to norm continuous if it is continuous from the weak topology of B to the strong topology of F.
We also need the following lemmas for the proof of our main results.
Lemma 2.1. [14]. Let q > 1 and r > 0 be two fixed real numbers. Let B be a uniformly convex Banach space if and only if there exists a continuous strictly increasing and convex function g: [0, +∞) → [0, +∞), g(0) = 0 such that
for all x, y ∈ B r = {x ∈ B: ||x|| ≤ r} and λ ∈ [0, 1], where ς q (λ) = λ(1 - λ)q+ λq(1 - λ).
For case q = 2, we have
Lemma 2.2. [15]. Let B be a uniformly convex and uniformly smooth Banach space.
We have
Next, we recall the concept of the generalized f-projection operator. Let G: B* × C → ℝ ∪ {+∞} be a functional defined as follows:
where ξ ∈ B*, ρ is positive number and f: C → ℝ ∪ {+∞} is proper, convex, and lower semi-continuous. From definitions of G and f, it is easy to see the following properties:
-
(i)
(||ξ|| - ||x||)2 + 2ρf(x) ≤ G(ξ, x) ≤ (||ξ|| + ||x||)2 + 2ρf(x);
-
(ii)
G(ξ, x) is convex and continuous with respect to x, when ξ is fixed;
-
(iii)
G(ξ, x) is convex and lower semicontinuous with respect to ξ, when x is fixed.
Definition 2.3. Let B be a real Banach space with its dual B*. Let C be a nonempty closed convex subset of B. We say that is a generalized f-projection operator if
In this article, we fixed ρ = 1, we have
For the generalized f-projection operator, Wu and Hung [13] proved the following basic properties.
Lemma 2.4. [16]. Let B be a reflexive Banach space with its dual B* and let C be a nonempty closed convex subset of B. The following statement holds:
-
(i)
is nonempty closed convex subset of C for all ξ ∈ B*;
-
(ii)
if B is smooth, then for all ξ ∈ E*, if and only if
-
(iii)
if B is smooth, then for any ξ ∈ B*, , where ∂f is the subdifferential of the proper convex and lower semi-continuous functional f.
Lemma 2.5. [16]. If f(x) ≥ 0 for all x ∈ C, then for any ρ > 0, we have
Lemma 2.6. [2]. Let B be a reflexive strictly convex Banach space with its dual B* and let C be a nonempty closed convex subset of B. If f: C → ℝ ∪ {+∞} is proper, convex, and lower semi-continuous, then
-
(i)
is single valued and norm to weak continuous;
-
(ii)
if B has the property (h), that is, for any sequence {x n } ⊂ B, x n ⇀ x ∈ E and ||x n || → ||x||, implies x n → x, then is continuous.
Defined the functional G2: B × C → ℝ ∪ {+∞} by
3. Algorithms
First, we establish a useful Lemma for solving the new system of generalized mixed variational inequalities is equivalent to find a fixed point of generalized f-projection operator. For this purpose, we recall the following result.
Lemma 3.1. Let C be nonempty subset of a reflexive, strictly convex and smooth Banach space B. If f1, f2, f3: C → (-∞, +∞] are proper, convex, and lower semi-continuous, then (x*, y*, z*) is a solution of problem (★) is equivalent to find x*, y*, and z* such that u* ∈ T1(y*), v* ∈ T2(z*), w* ∈ T3(x*) and
Proof. Since B is a reflexive strictly convex and smooth Banach space, we know that J is single-valued and is well defined and single valued. In fact, (x*, y*, z*) is a solution of problem (★) if and only if
if and only if for all x ∈ C,
By Lemma 2.4 (ii), if and only if
This complete the proof.
Algorithm 3.2. For arbitrarily chosen initial points x0, y0, z0 ∈ C; compute the sequences {x n }, {y n }, {z n } such that
where {α n }, {β n }, {γ n } ⊂ [0, 1], ∀n ≥ 0.
Algorithm 3.3. For arbitrarily chosen initial points x0, y0, z0 ∈ C; compute the sequences {x n }, {y n }, {z n } such that
where {α n } ⊂ [0, 1], ∀n ≥ 0.
If f1(x) = f2(x) = f3(x) = 0, ∀x ∈ C, then Algorithm 3.2 reduces to the following iterative method for solving (SGVIP) problem (1.1).
Algorithm 3.4. For arbitrarily chosen initial points x0, y0, z0 ∈ C; compute the sequences {x n }, {y n }, {z n } such that
where {α n }, {β n }, {γ n } ⊂ [0, 1], ∀n ≥ 0.
If γ n = 0, f3(x) = 0 and T3(y) = 0, ∀x, y ∈ C, then Algorithm 3.2 reduces to the following iterative method for solving problem (1.2).
Algorithm 3.5. For arbitrarily chosen initial points x0, y0, ∈ C; compute the sequences {x n },{y n } such that
where {α n }, {β n } ⊂ [0, 1], ∀n ≥ 0.
If β n = γ n = 0, T = T1 = T2 = T3, f2(x) = f3(x) = 0, ∀x ∈ C, then Algorithm 3.2 reduces to the following iterative method for solving problem (1.3).
Algorithm 3.6. For arbitrarily chosen initial points x0 ∈ C; compute the sequence {x n } such that
where {α n } ⊂ [0, 1], ∀n ≥ 0.
4. Existence and Convergence Theorems
Now, we state and prove the main results of this study.
Theorem 4.1. Let C be a nonempty, closed convex subset of a uniformly convex and uniformly smooth Banach space B with dual space B* and 0 ∈ C. If the upper semi-continuous set-valued mappingswith closed values and the proper convex lower semi-continuous mapping f1, f2, f3: C → ℝ ∪ {+∞} satisfy the following conditions:
-
(i)
f k (x) ≥ 0 for all x ∈ C and f k (0) = 0 for k = 1, 2, 3;
-
(ii)
for any x ∈ C and any z k ∈ T k (x), 〈z k , J*(Jx - z k )〉 ≥ 0 for k = 1, 2, 3;
-
(iii)
the set-valued mappings J - T k are compact for k = 1, 2, 3;
-
(iv)
0 < a ≤ α n ≤ b < 1, 0 < c ≤ β n ≤ d < 1 and 0 < e ≤ γ n ≤ h < 1, ∃a, b, c, d, e, h ∈ (0, 1).
Then problem (★) has a solution (x*, y*, z*) and the sequences {x n }, {y n }, and {z n } defined by Algorithm 3.2 have convergent subsequences, andsuch that, and as i → ∞, respectively.
Proof. Since B is a uniformly convex and uniformly smooth Banach space, we know that J is a bijection from B onto B* and uniformly continuous on any bounded subsets of B. Hence is well defined and single-valued and the sequences {x n }, {y n } and {z n } are well defined.
Let G2(x, y) = G(Jx, y). Then, for any x ∈ C,
From Lemma 2.5 and the above equation, we have
Similarly proof, we also have
and
By Lemma 2.2 and condition (ii), we obtain
It follows that
and
Hence, the sequences , and are bounded. So, we take a positive number r1, r2, r3, r4, r5, r6 such that and . We choose a number r = max{r1, r2, r3, r4, r5, r6} such that , by Lemma 2.1, for q = 2 there exists a continuous, strictly increasing, and convex function g: [0, ∞) → [0, ∞) with g(0) = 0 such that for α n , β n , γ n ∈ [0, 1], we have
and
We compute
From above, we obtain that
By the condition (iv), we have
Taking the sum for n = 0, 1, 2,..., m in the above inequality, we get
and
It is easy to know that
Hence, there exist subsequences and such that and
By property of functional g, we have
Similarly, we can proof that
Since {y n } is bounded sequence and (J - T1) is compact on C, without loss of generality there exist convergence subsequences say such that
By the continuity of the , we have
Again since {x n }, {z n } are bounded and (J - T2), (J - T3) are compact on C, without loss of generality there exist a convergence subsequence say and such that
and
By the continuity of and , we have
and
Let , and .
By using the triangle inequality, we have
From (4.6) and (4.9), we also have
From Algorithm 3.2 and (4.7), we obtain
Since above equations (4.7) and (4.12), we have
So,
It follows that
In the same way, we apply Algorithm 3.2, equations (4.7) and (4.13), we also have
We can show that
Similarly, we have and . Let u* = Jy* - u0, v* = Jz* - v0, and w* = Jx* - w0. Since T1, T2, and T3 are upper semi-continuous with closed values, T1, T2, and T3 are closed, and then u* = T1y*, v* = T2z*, and w* = T3x*. It follows from Algorithm 3.2 and the continuity of the operators , and that
This complete of the proof.
Theorem 4.2. Let C be a nonempty closed convex subset of a uniformly convex and uniformly smooth Banach space B with dual space B* and 0 ∈ C. If the upper semi-continuous set-valued mappingswith closed values, and the proper convex lower semi-continuous mapping f1, f2, f3: C → ℝ ∪ {+∞} satisfy the following conditions:
-
(i)
f k (x) ≥ 0 for all x ∈ C and f k (0) = 0 for k = 1, 2, 3;
-
(ii)
for any x ∈ C and any z k ∈ T k (x), 〈z k , J*(Jx - z k )〉 ≥ 0 for k = 1, 2, 3;
-
(iii)
the set-valued mappings J - T k are compact for k = 1, 2, 3;
-
(iv)
0 < a ≤ α n ≤ b < 1, ∃a, b ∈ (0, 1).
Then problem (★) has a solution (x*, y*, z*) and the sequences {x n }, {y n }, and {z n } defined by Algorithm 3.3 have convergent subsequences, andsuch that, andas i → ∞, respectively.
Proof. In this instance, (4.2) and (4.3) become
and
Hence, the sequences , and are bounded. Take a positive number r1, r2, r3, r4, r5, r6 such that , and . We choose a number r = max{r1, r2, r3, r4, r5, r6} such that , by Lemma 2.1, for q = 2 there exists a continuous, strictly increasing, and convex function g: [0, ∞) → [0, ∞) with g(0) = 0 such that for α n ∈ [0, 1], we have
Similarly proof of Theorem 4.1, we obtain that
Since {y n }, {z n }, and {x n } are bounded sequences, (J - T1), (J - T2), and (J - T3) are compact on C and by the continuity of the , and , we have
Hence, we obtain that .
By Algorithm 3.3, we get
and
It follows from above, we obtain that and . Similarly to the proof of Theorem 4.1, we can obtain this Theorem.
If f1(x) = f2(x) = f3(x) = 0, ∀x ∈ C, then the following theorem can be obtained from Theorem 4.1 directly.
Corollary 4.3. Let C be a nonempty, closed convex subset of a uniformly convex and uniformly smooth Banach space B with dual space B* and 0 ∈ C. If the upper semi-continuous set-valued mappings with closed values satisfy the following conditions:
-
(i)
for any x ∈ C and any z k ∈ T k (x), 〈z k , J*(Jx - z k )〉 ≥ 0 for k = 1, 2, 3;
-
(ii)
the set-valued mappings J - T k are compact for k = 1,2, 3;
-
(iii)
0 < a ≤ α n ≤ b < 1, 0 < c ≤ β n ≤ d < 1 and 0 < e ≤ γ n ≤ h < 1, ∃a, b, c, d, e, h ∈ (0, 1).
Then problem (1.1) has a solution (x*, y*, z*) and the sequences {x n }, {y n }, and {z n } defined by Algorithm 3.4 have convergent subsequences, andsuch that, andas i → ∞, respectively.
If x n = z n , f3(x) = 0, and T3(y) = 0, ∀x, y ∈ C, then the following theorem can be obtained from Theorem 4.1 directly.
Corollary 4.4. Let C be a nonempty closed convex subset of a uniformly convex and uniformly smooth Banach space B with dual space B* and 0 ∈ C. If the upper semi-continuous set-valued mappingswith closed values and the proper convex lower semi-continuous mapping f1, f2: C → ℝ ∪ {+∞} satisfy the following conditions:
-
(i)
f k (x) ≥ 0 for all x ∈ C and f k (0) = 0 for k = 1, 2;
-
(ii)
for any x ∈ C and any z k ∈ T k (x), 〈z k , J*(Jx - z k )〉 ≥ 0 for k = 1, 2;
-
(iii)
the set-valued mappings J - T k are compact for k = 1, 2;
-
(iv)
0 < a ≤ α n ≤ b < 1 and 0 < c ≤ β n ≤ d < 1, ∃a, b, c, d ∈ (0, 1).
Then problem (1.2) has a solution (x*, y*) and the sequences {x n } and {y n } defined by Algorithm 3.5 have convergent subsequencesandsuch thatandas i → ∞, respectively.
If x n = y n = z n , T = T1 = T2 = T3, and f2(x) = f3(x) = 0, ∀x ∈ C, then the following theorem can be obtained from Theorem 4.1 directly.
Corollary 4.5. Let C be a nonempty closed convex subset of a uniformly convex and uniformly smooth Banach space B with dual space B* and 0 ∈ C. If the upper semi-continuous set-valued mappingswith closed values and the proper convex lower semi-continuous mapping f1: C → ℝ ∪ {+∞} satisfy the following conditions:
-
(i)
f 1 (x) ≥ 0 for all x ∈ C and f 1 (0) = 0;
-
(ii)
for any x ∈ C and any z ∈ T(x), 〈z, J*(Jx - z)〉 ≥ 0;
-
(iii)
the set-valued mappings J - T is compact;
-
(iv)
0 < a ≤ α n ≤ b < 1, ∃a, b ∈ (0, 1).
Then problem (1.3) has a solution x* and the sequence {x n } defined by Algorithm 3.6 has a convergent subsequencesuch thatas i → ∞.
Remark 4.6. Theorems 4.1, 4.2, and Corollary 4.3 generalize and improve the main result in [1].
Our results generalize and extend the main result of [8] from a Hilbert space to a Banach space.
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Acknowledgements
This research was partially supported by the "Centre of Excellence in Mathematics", the Commission on High Education, Ministry of Education, Thailand (under the project No. RG-1-53-03-2). Moreover, Mr. Nawitcha Onjai-uea was supported by the "Centre of Excellence in Mathematics", the Commission on High Education for the Ph.D. Program at KMUTT.
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Onjai-uea, N., Kumam, P. Existence and convergence theorems for the new system of generalized mixed variational inequalities in Banach spaces. J Inequal Appl 2012, 9 (2012). https://doi.org/10.1186/1029-242X-2012-9
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DOI: https://doi.org/10.1186/1029-242X-2012-9