TAILIEUCHUNG - Báo cáo hóa học: "Research Article A Generalization of Kannan’s Fixed Point Theorem"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article A Generalization of Kannan’s Fixed Point Theorem | Hindawi Publishing Corporation Fixed Point Theory and Applications Volume 2009 Article ID 192872 10 pages doi 2009 192872 Research Article A Generalization of Kannan s Fixed Point Theorem Yusuke Enjouji Masato Nakanishi and Tomonari Suzuki Department of Mathematics Kyushu Institute of Technology Tobata Kitakyushu 804-8550 Japan Correspondence should be addressed to Tomonari Suzuki suzuki-t@ Received 22 December 2008 Accepted 23 March 2009 Recommended by Jerzy Jezierski In order to observe the condition of Kannan mappings we prove a generalization of Kannan s fixed point theorem. Our theorem involves constants and we obtain the best constants to ensure a fixed point. Copyright 2009 Yusuke Enjouji et al. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. 1. Introduction A mapping T on a metric space X d is called Kannan if there exists a e 0 1 2 such that d Tx Ty ad x Tx ad y Ty for all x y e X. Kannan 1 proved that if X is complete then every Kannan mapping has a fixed point. It is interesting that Kannan s theorem is independent of the Banach contraction principle 2 . Also Kannan s fixed point theorem is very important because Subrahmanyam 3 proved that Kannan s theorem characterizes the metric completeness. That is a metric space X is complete if and only if every Kannan mapping on X has a fixed point. Recently Kikkawa and Suzuki proved a generalization of Kannan s fixed point theorem. See also 4-8 . Theorem see 9 . Define a nonincreasing function y from 0 1 2 into 1 2 1 by 1 VW 1 a if 0 a V2 - 1 1 if V2 - 1 a 2. 2 Fixed Point Theory and Applications Let T be a mapping on a complete metric space X d . Assume that there exists a e 0 1 2 such that ự à d x Tx d x ỳ implies d Tx Ty ad x Tx ad y Ty for all x y e X. Then T has a unique fixed point z. Moreover lim T x z .

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