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Strong convergence of composite general iterative methods for one-parameter nonexpansive semigroup and equilibrium problems
Journal of Inequalities and Applications volume 2012, Article number: 131 (2012)
Abstract
In this paper, we introduce both explicit and implicit schemes for finding a common element in the common fixed point set of a one-parameter nonexpansive semigroup {T(s)| 0 ≤ s < ∞} and in the solution set of an equilibrium problems which is a solution of a certain optimization problem related to a strongly positive bounded linear operator. Strong convergence theorems are established in the framework of Hilbert spaces. As an application, we consider the optimization problem of a k-strict pseudocontraction mapping. The results presented improve and extend the corresponding results of many others.
2000 AMS Subject Classification: 47H09; 47J05; 47J20; 47J25.
1. Introduction
Let H be a real Hilbert space with inner product 〈·,·〉 and norm || · ||. Recall, a mapping T with domain D(T) and range R(T) in H is called nonexpansive iff for all x, y ∈ D(T),
Let C be a closed convex subset of a Hilbert space H, a family ℑ = {T(s)| 0 ≤ s < ∞} of mappings of C into itself is called a one-parameter nonexpansive semigroup on C iff it satisfies the following conditions:
-
(a)
T(s + t) = T(s)T(t) for all s, t ≥ 0 and T(0) = I;
-
(b)
||T(s)x - T(s)y|| ≤ ||x - y|| for all x, y ∈ C and s ≥ 0.
-
(c)
the mapping T(·)x is continuous, for each x ∈ C.
We denote by F(ℑ) the set of common fixed points of {T(t): t ≥ 0}. That is, F(ℑ) = ∩0 ≤ s < ∞F(T(s)). It is clear that T(s)T(t) = T(s + t) = T(t)T(s) for s, t ≥ 0.
Recall that f is called to be weakly contractive [1] iff for all x, y ∈ D(T),
for some φ: [0, +∞) → [0, +∞) is a continuous and strictly increasing function such that φ is positive on (0, +∞) and φ(0) = 0. If φ(t) = (1 - k)t, then f is called to be contractive with the contractive coefficient k. If φ(t) ≡ 0, then f is said to be nonexpansive.
Let C be a nonempty closed convex subset of H and F: C × C → R be a bifunction, where R is the set of real numbers. The equilibrium problem (for short, EP) is to find x ∈ C such that for all y ∈ C,
The set of solutions of (1.1) is denoted by EP(F). Given a mapping T: C → H, let F(x, y) = 〈Tx, y - x〉 for all x, y ∈ C. Then, x ∈ EP(F) if and only if x ∈ C is a solution of the variational inequality 〈Tx, y - x〉 ≥ 0 for all y ∈ C. In addition, there are several other problems, for example, the complementarity problem, fixed point problem and optimization problem, which can also be written in the form of an EP. In other words, the EP is an unifying model for several problems arising in physics, engineering, science, optimization, economics, etc. In the last two decades, many papers have appeared in the literature on the existence of solutions of EP; see, for example [2–5] and references therein. Some solution methods have been proposed to solve the EP; see, for example, [6–12] and references therein.
To study the equilibrium problems, we assume that the bifunction F: C × C → R satisfies the following conditions:
(A1) F(x, x) = 0 for all x ∈ C;
(A2) F is monotone, i.e., F(x, y) + F(y, x) ≤ 0 for all x, y ∈ C;
(A3) for each x, y, z ∈ C,
(A4) for each x ∈ C, y α F(x, y) is convex and lower semi-continuous.
Recently, Takahashi and Takahashi [10] introduced the following iterative method
for approximating a common element in the fixed point set of a single nonexpansive mapping and in the solution set of the equilibrium problem. To be more precise, they proved the following Theorem.
Theorem TT Let C be a nonempty closed convex subset of H. Let F be a bifunction from C × C to R satisfying (A1)-(A4) and let T be a nonexpansive mapping of C into H such that F (T) ∩ EP (F) ≠ ∅. Let f be a contraction of H into itself and let {x n } and {y n } be sequences generated by x1 ∈ H and
where {α n } ∈ 0[1] and {r n } ⊂ (0, ∞) satisfy
lim infn→∞r n > 0, and . Then {x n } and {y n } converge strongly to z ∈ F(T) ∩ EP (F), where z = P(T)∩EP(F)f(z).
Subsequently, many authors studied the problem of finding a common element in the fixed point set of nonexpansive mappings, in the solution set of variational inequalities and in the solution set of equilibrium problems, for instance see [10–20].
Iterative methods for nonexpansive mappings have recently been applied to solve convex minimization problems; see, e.g., [21–26] and the references therein. Let A be a strongly positive linear bounded operator (i.e., there is a constant such that , ∀x ∈ H), and T be a nonexpansive mapping on H. A typical problem is to minimize a quadratic function over the set of the fixed points of a nonexpansive mapping on a real Hilbert space H:
where F(T) is the fixed point set of the mapping T on H and b is a given point in H.
Starting with an arbitrary initial x0 ∈ H, define a sequence {x n } recursively by
It is proved [23] (see also [24]) that the sequence {x n } generated by (1.3) converges strongly to the unique solution of the minimization problem (1.2) provided the sequence {α n } satisfies certain conditions.
In 2007, related to a certain optimization problem, Marino and Xu [27] introduced the following viscosity approximation method for nonexpansive mappings. Let f be a contraction on H. Starting with an arbitrary initial x0 ∈ H, define a sequence {x n } recursively by
and proved that if the sequence {α n } satisfies appropriate conditions, the sequence {x n } generated by (1.4) converges strongly to the unique solution of the variational inequality
which is the optimality condition for the minimization problem
where h is a potential function for γf (that is, h'(x) = γf(x) for x ∈ H).
In 2009, Cho et al. [28] extended the result of Marino and Xu [27] to the class of k-strictly pseudo-contractive mappings and proved the convergent theorem.
Motivated by the ongoing research and the above mentioned results, we introduce both explicit and implicit schemes for finding a common element in the common fixed point set of a one-parameter nonexpansive semigroup {T(s)| 0 ≤ s < ∞}, in the solution set of an equilibrium problems, in the solution set of variational inequalities in the framework of Hilbert spaces. The results presented in this paper improve and extend the corresponding results in [9, 10, 14, 15, 27–30].
In order to prove our main results, we need the following lemmas.
The following lemma can be found in [7].
Lemma 1.1 Let C be a nonempty closed convex subset of H and let F: C × C → R be a bifunction satisfying (A1)-(A4). Then, for any r > 0 and x ∈ H, there exists z ∈ C such that
Further, define
for all z ∈ H. Then the following hold:
-
(1)
T r is single-valued;
-
(2)
T r is firmly nonexpansive, i.e., for any x, y ∈ H,
(3)F(T r ) = EP(F);
-
(4)
EP(F) is closed and convex.
Remark 1.1 The mapping T r is also nonexpansive for all r > 0.
Lemma 1.2[27] Assume A is a strongly positive linear bounded operator on a Hilbert space H with coefficient and 0 < ρ ≤ ||A||-1. Then .
Lemma 1.3[31] Let C be a nonempty bounded closed convex subset of H and let ℑ = {T(s): 0 ≤ s <∞} be a nonexpansive semigroup on C, then for any h ≥ 0,
Lemma 1.4 Let C be a nonempty bounded closed convex subset of a Hilbert space H and ℑ = {T(t): 0 ≤ t <∞}be a nonexpansive semigroup on C. If {x n } is a sequence in C satisfying the properties:
(i)x n ⇀ z;
(ii) lim supt→∞lim supn→∞||T(t)x n - x n || = 0,
where x n ⇀ z denote that {x n } converges weakly to z, then z ∈ F(ℑ).
Proof. This Lemma is the continuous version of Lemma 2.3 of Tan and Xu[32]. This proof given in [32] is easily extended to the continuous case.
Lemma 1.5[33] Let C be a nonempty closed convex subset of a real Hilbert space H, T be nonexpansive mapping from C into self. Then the mapping I - T is demiclosed at zero, i.e.,
Lemma 1.6[22] Assume {a n } is a sequence of nonnegative real numbers such that
where {γ n } is a sequence in (0,1) and {δ n } is a sequence in R such that
-
(i)
.
-
(ii)
lim supn→∞δ n /γ n ≤ 0 or .
Then limn→∞a n = 0.
Lemma 1.7[34] Let {λ n } and {β n } be two nonnegative real number sequences and {α n } a positive real number sequence satisfying the conditions and or . Let the recursive inequality
be given, where ψ(λ) is a continuous and strict increasing function for all λ ≥ 0 with ψ(0) = 0. Then {λ n } converges to zero, as n → ∞.
2. Implicit viscosity iterative algorithm
Theorem 2.1 Let C be a nonempty closed convex subset of a Hilbert space H. Let F be a bifunction from C × C into R satisfying (A1)-(A4). Let f be a weakly contractive mapping with a function φ on H, A a strongly positive linear bounded operator with coefficient on H, ℑ = {T(s): s ≥ 0} be a nonexpansive semigroup on C, respectively. Assume that Ω:= F(ℑ)∩EP(F) ≠ ∅, {α n }, {β n }⊂(0,1), {t n }⊂(0,∞) be real sequences satisfying the conditions
then for any and any r > 0, there exists a unique sequence {x n } ⊂ H satisfying the following condition
Furthermore, the sequence {x n } converges strongly to z* ∈ Ω which uniquely solves the following variational inequality
Proof. We divide the proof into six steps.
Step 1.
Since α n → 0 as n → ∞, we may assume, with no loss of generality, that α n < ||A||-1 for all n ≥ 1. Then, for all n ≥ 1.
First, we show that the sequence {x n } generated from (2.1) is well defined. For each n ≥ 1, define a mapping in H as follows
Observe from Lemma 1.1 that T r be a nonexpansive for each r > 0, thus we have that for any x, y ∈ C,
where ψ(x - y) = α n γφ(||x - y||). This shows that is a weakly contractive mapping with a function ψ on H for each n ≥ 1. Therefore, by Theorem 5 of [11], has a unique fixed point (say) x n ∈ H. This means that Eq.(2.1) has a unique solution for each n ≥ 1, namely,
where note from Lemma 1.1 that u n can be re-written as u n = T r x n .
Next, we show that {x n } is bounded. Indeed, for any z ∈ Ω, note that z = T r z. It follows from Lemma 1.1 that
Notice that
It follows that
Therefore,
which implies that {φ(||x n - z||)} is bounded. We obtain that {||x n - z||} is bounded by the property of φ. So {x n } is bounded and so are {u n }, {z n }, {f(u n )}, {Az n } from Eq.(2.3) and Eq.(2.4). We may, without loss of generality, assume that there exists a bounded set K ⊂ C such that x n , u n , z n ∈ K, for each n ≥ 1.
Step 2. We claim that there exists a subsequence {n k } of {n} such that and z* ∈ F(ℑ).
Indeed, for any z ∈ Ω, denote , then ||w n -z|| ≤ ||u n -z|| ≤ ||x n -z||. From Eq.(2.1), the boundedness of {f(x n )}, {Az n }, {u n }, {w n } and the conditions limn→∞α n = limn→∞β n = 0, we see that
and
In view of Eq.(2.6) and Eq.(2.7), we obtain that
Let , then K1 is a nonempty bounded closed convex subset of H and T(s)-invariant. Since {x n } ⊂ K1 and K1 is bounded, there exists r > 0 such that K1 ⊂ B r , it follows from Lemma 1.3 that
By virtue of Eq.(2.8) and Eq.(2.9), we arrive at
On the other hand, since {x n } is bounded, we know that there exists a subsequence of {x n } such that . By Lemma 1.4 and Eq.(2.10), we arrive at z* ∈ F(ℑ).
In Eq.(2.5), interchange z* and z to obtain
where . From , we get that
namely,
which implies that as k → ∞ by the property of ψ, and thus .
Step 3. We shall show that limn→∞||u n - x n || = 0 and z* ∈ EP (F), where z* is obtained in Step 2.
Since T r is firmly nonexpansive, from Lemma 1.1(2), we see for any z ∈ Ω that
from which it follows that
On the other hand, it follows from Eq.(2.1) and Eq.(2.11) that
Moreover, we have from Eq.(2.12) that
where M is a constant such that M ≥ max{supn ≥ 1{γ||x n - z||2}, supn ≥ 1{||γf(z) - Az|| ||x n - z||}}. From the condition α n → 0(n → ∞), we get from Eq.(2.13) that lim supn→∞||u n - x n || = 0, which implies that as n → ∞, ||u n - x n || → 0. Because ||u n - x n || = ||T r x n - x n || → 0(n → ∞), we see from Lemma 1.5 and Lemma 1.1 that z* ∈ F(T r ) = EP (F). Therefore, z* ∈ Ω.
Step 4. We claim that z* is the unique solution of the variational inequality (2.2).
Firstly, we show the uniqueness of the solution to the variational inequality (2.2) in Ω. In fact, suppose p, q ∈ Ω satisfy Eq.(2.2), we see that
Adding these two inequalities (2.14) (2.15) yields
thus
From , we get that
By the property of φ, we must have p = q and the uniqueness is proved.
Next we show that z* is a solution in Ω to the variational inequality (2.2).
In fact, since
we derive that
For any z ∈ Ω, it follows that
Now we consider the right side of Eq.(2.16). Observe from Eq.(2.1) that
Note from z ∈ Ω ⊂ EP(F) that F (z, u n ) ≥ 0, then F(u n , z) ≤ -F(z, u n ) ≤ 0, which implies that
On the other hand, it is easily seen that is monotone, that is
Thus, we obtain from Eq.(2.16) that
Also, we notice from || x n - u n || → 0 (n → ∞) and that
and
Now replacing n in Eq.(2.17) with n k and taking limsup, we have from Eq.(2.18) and Eq.(2.19) that
for any z ∈ Ω. This is, z* ∈ Ω is unique solution of Eq.(2.2).
Step 5. We claim that
To show Eq.(2.21), we may choose a subsequence of {x n } such that
Since is bounded, we can choose a subsequence of converges weakly to z.
We may, assume without loss of generality, that , then , note from Step 2 and Step 3 that z ∈ Ω and thus . It follows from Eq.(2.22) that
So Eq.(2.21) holds, thanks to Eq.(2.20).
Step 6. We claim that x n → z* as n → ∞.
First, from Eq.(2.8) and Eq.(2.21) we conclude that
Now we compute ||x n - z*||2 and have the following estimates:
It follows that
By virtue of the boundedness of {x n }, Eq.(2.23) and the condition α n → 0(n → ∞), we can conclude that limn→∞φ(||x n - z*||) = 0. By the property of φ, we obtain that x n → z* ∈ Ω as n → ∞. This completes the proof of Theorem 2.1.
From Theorem 2.1, we can derive the desired conclusion immediately for a single nonexpansive mapping T.
Corollary 2.1 Let C be a nonempty closed convex subset of a Hilbert space H. Let F a bifunction from C × C → R satisfying (A1)-(A4), f be a weakly contractive mapping with a function φ on H, A a strongly positive linear bounded operator with coefficient on H, and T be a nonexpansive mapping from C into itself, respectively. Assume that Ω = F(T) ∩ EP (F) ≠ ∅, {α n }, {β n } ⊂ (0, 1) are real sequences such that:limn→∞α n = 0, β n = o(α n ). Then for any and any r > 0, there exists a unique {x n } ⊂ H such that
Furthermore, the sequence {x n } converges strongly to z* ∈ Ω which solves the variational inequality (2.2).
Remark 2.1 Putting β n = 0, φ(t) = (1 - k)t and u n = x n in Theorem 2.1, we can obtain Theorem 3.1 in [30].
Remark 2.2 The parameter γ can be allowed to take the coefficient in Theorem 2.1 and Corollary 2.1. Our results contain the ones in [23] and [27] as special cases.
3. Explicit viscosity iterative algorithm
Theorem 3.1 Let C be a nonempty closed convex subset of a Hilbert space H. Let F a bifunction from C × C → R satisfying (A1)-(A4), f be a weakly contractive mapping with a function φ on H, A a strongly positive linear bounded operator with coefficient on H, and ℑ = {T(s): s ≥ 0} be a nonexpansive semigroup on C, respectively. Assume that Ω = F(ℑ)∩EP(F) ≠ ∅, {α n }, {β n } ⊂ (0, 1), {t n } ⊂ (0, ∞) are real sequences satisfying the following restrictions:
(C1) limn→∞α n = 0, , ;
(C2) limn→∞β n = 0, ;
(C3) , .
For any and any r > 0, let a sequence {y n } be iteratively generated from y1 ∈ C by:
Then {y n } converges strongly to the unique solution in F to the inequality (2.2).
Proof. Firstly, we show that {y n } is bounded.
Since α n → 0 as n → ∞, we may assume, with no loss of generality, that α n < ||A||-1 for all n ≥ 1. Then, for all n ≥ 1.
For any z ∈ Ω, note from Lemma 1.1 that v n can be re-written as v n = T r y n for each n ≥ 1 and z = T r z. It follows from Lemma 1.1 that
Notice that
From which it follows that
By induction,
and {y n } is bounded, which leads to the boundedness of {v n }, {z n }, {f(v n )}, {Az n }. We may, without loss of generality, assume that there exists a bounded set K ⊂ C such that y n , v n , z n ∈ K, for each n ≥ 1.
Using a similar method of proof as in the Step 2 of the proof of Theorem 2.1, we can conclude that
and
Let , then K1 is a nonempty bounded closed convex subset of H and T (s)-invariant. Since {yn+1} ⊂ K1 and K1 is bounded, there exists r > 0 such that K1 ⊂ B r , it follows from Lemma 1.3 that
By virtue of Eq.(3.2) and Eq.(3.4), we arrive at
Next we shall prove that yn+1- y n → 0 as n → ∞.
Note that
Also
and
where . Now we compute ||w n - wn-1||,
Substituting Eq.(3.7)-(3.9) into Eq.(3.6), we arrive at
for some positive constant M. Thanks to the conditions (C1) - (C3) and Lemma 1.7, we conclude that
Now, we show
Indeed, using a similar method of proof as in the Step 3 of the proof of Theorem 2.1, we can obtain that
from which it follows that
where M1 is an appropriate constant such that M1 = max{supn ≥ 1{γ||y n - z|| ||yn+1- z||}, supn ≥ 1{||γf(z) - Az|| ||yn+1- z||}, supn ≥ 1{||y n - z|| + ||yn+1- z||}}. From the condition α n → 0(n → ∞) and Eq.(3.10), we get that lim supn→∞||v n - y n || = 0, which implies that the Eq.(3.11) holds.
It follows from Theorem 2.1 that there is a unique solution z* ∈ Ω to the variational inequality (2.2).
Next, we show that lim supn→∞〈γf(z*) - Az*, yn+1- z*〉 ≤ 0
Indeed, we can take a subsequence of such that
We may assume that since {yn+1} is bounded. From Eq.(3.5) and Lemma 1.4, we conclude z ∈ F (ℑ). Similarly, from Eq.(3.11) and Lemma 1.1 and Lemma 1.5, we have z ∈ EP(F). Therefore, z ∈ Ω.
In view of the variational inequality (2.2), we conclude
From (3.4), we see that
Finally, we show that y n → z*. As a matter of fact,
where
Since {y n } is bounded, there must exist a constant M2 > 0 such that
It then follows from Eq.(3.13) that
where B n = 2〈z n - z*, γf(z*) - Az*〉 + α n M2. From the conditions (C1) - (C2), Eq.(3.12) and Lemma 1.6, we obtain from Eq.(3.14) that y n → z* in norm. This completes the proof of Theorem 3.1.
From Theorem 3.1, we can derive the desired conclusion immediately for a nonexpansive mapping T.
Corollary 3.1 Let H be a Hilbert space, C be a nonempty closed convex subset of H, F a bifunction from C × C → R satisfying (A1)-(A4). Let f be a weakly contractive mapping with a function φ on H, and A a strongly positive linear bounded operator with coefficient on H, and T be a nonexpansive mapping from C into itself. Assume that Ω = F(T) ∩ EP(F) ≠ ∅, for any and any r > 0, let y1 ∈ C, and {y n } be a sequence generated in
where {α n }, {β n } ⊂ (0, 1) are real sequences satisfying the conditions (C1) - (C2) in Theorem 3.1. Then the sequence {y n } converges strongly to z* ∈ Ω which uniquely solves the variational inequality (2.2).
Remark 3.1 Putting A = I, β n = 0 and φ(t) = (1 - k)t in Corollary 3.1, we can easily conclude Theorem TT [10].
Remark 3.2 Putting β n = 0, φ(t) = (1 - k)t and u n = x n in Theorem 3.1, we can obtain Theorem 3.2 in [30].
4. Application
In this section, we shall consider another class of important nonlinear operator: k-strict pseudocontractions.
Recall that a mapping S: C → C is said to be a k-strict pseudocontraction if there exists a constant k ∈ (0, 1) such that
for all x, y ∈ C. Note that the class of k-strict pseudocontractions strictly includes the class of nonexpansive mappings.
Corollary 4.1 Let C be a nonempty closed convex subset of a Hilbert space H, F be a bifunction from C × C → R satisfying (A1)-(A4). Let f be a weakly contractive mapping with a function φ on H, A a strongly positive linear bounded operator with coefficient on H, T: C → H be a k-strictly pseudo-contractive mapping for some 0 ≤ k < 1, respectively. Assume that Ω = F(T) ∩ EP(F) ≠ ∅, for any and any r > 0, let y1 ∈ C, and {y n } be a sequence generated in
where S: C → H is a mapping defined by Sx = kx + (1 - k)Tx and P C is the metric projection of H onto C, {α n }, {β n } ⊂ (0, 1) are real sequences satisfying the conditions (C1) - (C2) in Theorem 3.1. Then the sequence {y n } converges strongly to z* ∈ Ω which uniquely solves the variational inequality (2.2).
Proof. From Lemma 2.3 in [35], we see that S: C → H is a nonexpansive mapping and F(T) = F(S). It follows from Lemma 2.2 [32] that, P C S: C → C is a nonexpansive mapping and F(P C S) = F(S) = F(T). Hence the result follows from Corollary 3.1.
Remark 4.1 Putting v n = y n and φ(t) = (1 - k)t in Corollary 4.1, we can obtain Theorem J in [29], Further, putting β n = 0, we can obtain Theorem CKQ in [28].
5. Numerical examples
Now, we give some real numerical examples in which the conditions satisfy the ones of Theorems 3.1 and 2.1 and some numerical experiment results to explain the main results Theorems 3.1 and 2.1 as follows:
Example 5.1. Let H = R and C = 0[1]. For each x ∈ C, we define , A(x) = 2x, . Let , n ∈ N. For each (x, y) ∈ H × H, we define F(x, y) = x2 + y. Then {y n } is the sequence generated by
and y n → y* = 0 as n → ∞, where y* = 0 ∈ F(T) ∩ EP(F).
Proof. It is obvious that the bifunction F(x, y) satisfies the conditions (A1)-(A4) and is a weakly contractive mapping with a function on R, is a nonexpansive mapping on C and F(T) = {0}, A(x) = 2x is a strongly positive linear bounded operator with coefficient on R, and the bifunction F(x, y) = x2 + y satisfies conditions (A1)-(A4) and EP(F) = {y: y ≥ 0}. satisfy limn→∞α n = 0, , , limn→∞β n = 0, and F(T) ∩ EP(F) = {0}.
Hence, the conditions satisfy the ones of Theorem 3.1. Substituting all of the given conditions to the scheme (3.1), we have (5.1). Following the proof of Theorem 3.1, we easily obtain {y n } converges strongly to y* = 0 ∈ F(T) ∩ EP(F).
The proof is completed.
Example 5.2. Let C = 0[2], H, f, A, T, α n , β n , F be as in Example 5.1., F(T) ∩ EP(F) = {0, 2}. Then there exists a unique sequence {x n } ⊂ H satisfying the following equation
Furthermore, x n → x* = 2 as n → ∞, where x* = 2 ∈ F(T) ∩ EP(F).
Proof. As in the proof of Example 5.1, the conditions satisfy the ones of Theorem 2.1. Substituting all of the given conditions to the scheme (2.1), we have (5.2), and if x n ≠ 0 for each n, (5.2) is equal to the following equation
Following the proof of Theorem 2.1, we easily obtain {x n } converges strongly to x* = 2 ∈ F(T) ∩ EP(F). The proof is completed.
Next, we give the numerical experiment results using software Matlab 7.0 and get Figures 1 and 2, which show that the iteration processes of the sequence {y n } as initial point y(1) = 1, y(1) = 0.5 and the sequence {x n }, respectively. From the figures, we can see that {y n } converges to 0 and {x n } converges to 2, and the more the iteration steps are, the more fast the sequence {y n } and {x n } converges to 0 and 2, respectively.
References
Alber Ya I, Guerre-Delabriere S: Principles of weakly contractive maps in Hilbert spaces, New Results in Operator Theory. In Advances and Application. Volume 98. Edited by: Gohberg I, Lyubich Yu. Birkhauser, Basel; 1997:7–22.
Blum E, Oettli W: From optimization and variational inequalities to equilibrium problems. Math Stud 1994, 63: 123–145.
Flores-Bazan F: Existence theory for finite-dimensional pseudomonotone equilibrium problems. Acta Appl Math 2003, 77: 249–297. 10.1023/A:1024971128483
Hadjisavvas N, Komlósi S, Schaible S: Handbook of Generalized Convexity and Generalized Monotonicity. Springer, Berlin; 2005.
Hadjisavvas N, Schaible S: From scalar to vector equilibrium problems in the quasimonotone case. J Optim Theory Appl 1998, 96: 297–309. 10.1023/A:1022666014055
Ceng LC, Yao JC: A hybrid iterative scheme for mixed equilibrium problems and fixed point problems. J Comput Appl Math 2008, 214: 186–201. 10.1016/j.cam.2007.02.022
Combettes PL, Hirstoaga SA: Equilibrium programming in Hilbert spaces. J Nonlinear Convex Anal 2005, 6: 117–136.
Flam SD, Antipin AS: Equilibrium programming using proximal-like algorithms. Math Program 1997, 78: 29–41.
Tada A, Takahashi W: Strong convergence theorem for an equilibrium problem and a nonexpansive mapping. In Nonlinear Analysis and Convex Analysis. Edited by: Takahashi W, Tanaka T. Yokohama, Yokohama; 2006:609–617.
Takahashi S, Takahashi W: Viscosity approximation methods for equilibrium problems and fixed point problems in Hilbert spaces. J Math Anal Appl 2007, 331: 506–515. 10.1016/j.jmaa.2006.08.036
Ye J, Huang J: Strong convergence theorems for fixed point problems and generalized equilibrium problems of three relatively quasi-nonexpansive mappings in Banach spaces. J Math Comput Sci 2011, 1: 1–18.
Ciric L, Olatinwo MO, Gopal D, Akinbo G: Coupled fixed point theorems for mappings satisfying a contractive condition of rational type on a partially ordered metric space. Adv Fixed Point Theory 2012.
Ceng LC, Yao JC: Hybrid viscosity approximation schemes for equilibrium problems and fixed point problems of infinitely many nonexpansive mappings. Appl Math Comput 2008, 198: 729–741. 10.1016/j.amc.2007.09.011
Ceng LC, Al-Homidan S, Ansari QH, Yao JC: An iterative scheme for equilibrium problems and fixed point problems of strict pseudo-contraction mappings. J Comput Appl Math 2009, 223: 967–974. 10.1016/j.cam.2008.03.032
Colao V, Marino G, Xu HK: An iterative method for finding common solutions of equilibrium and fixed point problems. J Math Anal Appl 2008, 344: 340–352. 10.1016/j.jmaa.2008.02.041
Chang SS, Joseph Lee HW, Chan CK: A new method for solving equilibrium problem fixed point problem and variational inequality problem with application to optimization. Nonlinear Anal 2009, 70: 3307–3319. 10.1016/j.na.2008.04.035
Plubtieng S, Punpaeng R: A new iterative method for equilibrium problems and fixed point problems of nonexpansive mappings and monotone mappings. Appl Math Comput 2008, 197: 548–558. 10.1016/j.amc.2007.07.075
Qin X, Shang M, Su Y: Strong convergence of a general iterative algorithm for equilibrium problems and variational inequality problems. Math Comput Model 2008, 48: 1033–1046. 10.1016/j.mcm.2007.12.008
Qin X, Shang M, Su Y: A general iterative method for equilibrium problems and fixed point problems in Hilbert spaces. Nonlinear Anal 2008, 69: 3897–3909. 10.1016/j.na.2007.10.025
Qin X, Cho YJ, Kang SM: Convergence theorems of common elements for equilibrium problems and fixed point problems in Banach spaces. J Comput Appl Math 2009, 225: 20–30. 10.1016/j.cam.2008.06.011
Deutsch F, Yamada I: Minimizing certain convex functions over the intersection of the fixed point sets of nonexpansive mappings. Numer Funct Anal Optim 1998, 19: 33–56.
Xu HK: Iterative algorithms for nonlinear operators. J London Math Soc 2002, 66: 240–256. 10.1112/S0024610702003332
Xu HK: An iterative approach to quadratic optimization. J Optim Theory Appl 2003, 116: 659–678. 10.1023/A:1023073621589
Yamada I: The hybrid steepest descent method for the variational inequality problem of the intersection of fixed point sets for nonexpansive mappings. In Inherently Parallel Algorithm for Feasibility and Optimization. Edited by: Butnariu K, Censor Y, Reich S. Elsevier, New York; 2001:473–504.
Yamada I, Ogura N, Yamashita Y, Sakaniwa K: Quadratic approximation of fixed points of nonexpansive mappings in Hilbert spances. Numer Funct Anal Optim 1998, 19: 165–190. 10.1080/01630569808816822
Geobel K, Kirk WA: Topics in Metric Fixed Point Theory. In Cambridge Studies in Advanced Mathematics. Volume 28. Cambridge University Press, Cambridge; 1990.
Marino G, Xu HX: A general iterative method for nonexpansive mappings in Hilbert spaces. J Math Anal Appl 2006, 318: 43–52. 10.1016/j.jmaa.2005.05.028
Cho YJ, Kang SM, Qin X: Some results on k-strictly pseudo-contractive mappings in Hilbert spaces. Nonlinear Anal 2009, 70: 1956–1964. 10.1016/j.na.2008.02.094
Jung JS: Strong convergence of iterative methods for k-strictly pseudo-contractive mappings in Hilbert spaces. Appl Math Comput 2010, 215: 3746–3753. 10.1016/j.amc.2009.11.015
Li S, Li L, Su Y: General iterative methods for a one-parameter nonexpansive semigroup in Hilbert space. Nonlinear Anal 2009, 70: 3065–3071. 10.1016/j.na.2008.04.007
Shimizu T, Takahashi W: Strong convergence to common fixed points of families of nonexpansive mappings. J Math Anal Appl 1997, 211: 71–83. 10.1006/jmaa.1997.5398
Tan KK, Xu HK: The nonlinear ergodic theorem for asymptotically nonexapansive mappings in Banach spaces. Proc Am Math Soc 1992, 114: 399–404. 10.1090/S0002-9939-1992-1068133-2
Browder FE: Nonlinear operators and nonlinear equations of evolution in Banach spaces. Proc Sympos Pure Math 1976, 18: 78–81.
Ceng LC, Tanaka T, Yao JC: Iterative construction of fixed points of nonself-mappings in Banach spaces. J Comput Appl Math 2007, 206: 814–825. 10.1016/j.cam.2006.08.028
Zhou H: Convergence theorems of fixed points for k-strict pseudo-contractions in Hilbert spaces. Nonlinear Anal 2008, 69: 456–462. 10.1016/j.na.2007.05.032
Acknowledgements
The authors are very grateful to the referees for their careful reading, comments and suggestions, which improved the presentation of this article. The first author was supported by the Natural Science Foundational Committee of Hebei Province(Z2011113) and Hebei Normal University of Science and Technology (ZDJS 2009 and CXTD2010-05).
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XX and SL carried out the proof of convergence of the theorems. LL, HS and LZ carried out the check of the manuscript. All authors read and approved the final manuscript.
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Xiao, X., Li, S., Li, L. et al. Strong convergence of composite general iterative methods for one-parameter nonexpansive semigroup and equilibrium problems. J Inequal Appl 2012, 131 (2012). https://doi.org/10.1186/1029-242X-2012-131
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DOI: https://doi.org/10.1186/1029-242X-2012-131