New Hybrid Iterative Schemes for an Infinite Family of Nonexpansive Mappings in Hilbert Spaces
© B. Guo and S.Wang. 2010
Received: 20 November 2009
Accepted: 4 February 2010
Published: 14 February 2010
We propose some new iterative schemes for finding common fixed point of an infinite family of nonexpansive mappings in a Hilbert space and prove the strong convergence of the proposed schemes. Our results extend and improve ones of Nakajo and Takahashi (2003).
1. Introduction and Preliminaries
Let be a Hilbert space and a nonempty closed convex subset of . Let be a nonlinear mapping of into itself. We use and to denote the set of fixed points of and the metric projection from onto , respectively.
Recall that is said to be nonexpansive if
for all .
For approximating the fixed point of a nonexpansive mapping in a Hilbert space, Mann  in 1953 introduced a famous iterative scheme as follows:
where is a nonexpansive mapping of into itself and is a sequence in . It is well known that defined in (1.2) converges weakly to a fixed point of .
Nakajo and Takahashi  proposed the following modification of Mann iteration method (1.2) for a single nonexpansive mapping in a Hilbert space :
where denotes the metric projection from onto a closed convex subset of . They proved that if the sequence is bounded above from one, then the sequence generated by (1.3) converges strongly to .
In this paper, we introduce some new iterative schemes for infinite family of nonexpansive mappings in a Hilbert space and prove the strong convergence of the algorithms. Our results extend and improve the corresponding one of Nakajo and Takahashi .
The following two lemmas will be used for the main results of this paper.
Lemma 1.2 (see ).
2. Main Results
where is a sequence in satisfying and is a sequence in satisfying . Then defined by (2.1) converges strongly to .
for all . So, is closed and convex for all and hence is also closed and convex for all . This implies that is well defined.
Therefore, and is nonempty for all . On the other hand, from the definition of , we see that for all .
for all . Since is bounded, is bounded for each .
for all . It follows from (2.7) and (2.10) that the limit of exists.
In view of Lemma 1.1, one sees that . This completes the proof.
where is a sequence in satisfying that . Then defined by (2.24) converges strongly to .
Set for all , and for all in Theorem 2.1. By Theorem 2.1, we obtain the desired result.
where is a strictly decreasing sequence in and set . Then defined by (2.25) converges strongly to .
This shows that for all . Therefore, for all . It follows that for all .
By using the method of Theorem 2.1, we can conclude that is bounded, , and as . This implies that as .
Finally, by using the method of Theorem 2.1, we can conclude that . This completes the proof.
In this paper, we extend result of Nakajo and Takahashi  from a single nonexpansive mapping to an infinite family of nonexpansive mappings.
The iterative schemes introduced in this paper are new and of independent interest.
It is of interest to extend the algorithm (2.25) to certain Banach spaces.
The work was supported by Youth Foundation of North China Electric Power University.
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