A fixed point result in banach spaces
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This document presents a fixed point theorem for mappings in Banach spaces. It establishes conditions under which such mappings have unique fixed points. Specifically, it proves that if a mapping F satisfies certain contraction conditions involving rational expressions, and the contraction coefficients satisfy certain inequalities, then F has a unique fixed point. The proof considers two cases for the rational expressions and shows that in both cases, the mapping defines a Cauchy sequence that converges to a fixed point. The result generalizes previous fixed point theorems established by other authors for non-expansive mappings.
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A Fixed Point Result in Banach Spaces
R.K.Sharma1
, Bharti Choure2
, R.K. Bhardwaj3
1&2
Department of Mathematics,B.U.I.T Bhopal-462026,India
3
Department of Mathematics, TRUBA, Institute of engineering & IT Bhopal
Email:rkbhardwaj100@gmail.com
Abstract
In the present paper we establish some fixed point theorems in Banach space taking rational expression. Our
Result Generalize the result of many authors.
Key words: Fixed point, common fixed point, rational expressions, Banach spaces
Introduction: Fixed point has drawn the attentions of the authors working in non-linear analysis, the study of
non-expansive mapping and the existence of fixed point. The non-expansive mappings include contraction as
well as contractive mappings. Browder [1] was the first mathematician to study non-expansive mappings; he
applied these results for proving the existence of solutions of certain integral equations.
It is well known that differential and the integral equations that arise in physical problems are generally
non-linear, therefore the fixed point technique provides a powerful tool for obtaining the solutions of these
equations which otherwise are difficult to solve by ordinary methods. No doubt, it is also true that some
qualitative properties of the solution of related equations is lost by functional analysis approach. Many attempts
have been made in this direction to formulate fixed point theorems. Schauder, J. formulated the well known
Schauder’s fixed point principle in 1930.
Browder [1], Gohde [6] and Kirk [10] have independently proved a fixed point theorem for non-expansive
mappings defined on a closed bounded and convex subset of a uniformly convex Banach space and in the spaces
with richer generalizations of non-expansive mappings, prominent being Datson [2], Emmanuele [3], Goebel
[4], Goebel and Zlotkienwicz [5], Iseki [7], Sharma & Rajput [11], Singh and Chatterjee [13]. They have
derived valuable results with non-contraction mapping in Banach space.
Our object in this chapter is to prove some fixed and common fixed point theorems using Banach space.
Our results include the results of Goebel and Zlotkiewicz [5], Iseki [7], Sharma and Bajaj [12], Khan
[9], Jain and Jain [8]. We shall prove:-
Theorem-1 :
Let F be a mapping of a Banach space x into itself. If F satisfies the following conditions;
1. F2
= I, where I is the identity mapping. ……….(1.1)
2. ‖ ( ) ( )‖ ……….(1.2)
≤ a1 [‖ ( )‖ ‖ ( )‖] + a2 [‖ ‖
+ Max { }
Where
P =
‖ ( )‖‖ ( )‖ ‖ ( )‖ ‖ ( )‖
‖ ‖
‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖
‖ ‖
For every x,y X, where 0 < a1,a2,a3 and 4a1 + a2 + 8a3 < 2, then F has a fixed point, if a2 + a3 <
1,then F has a unique fixed point.
Proof: Suppose x be a point in Banach space X. Taking
y = (F+I) (x)
z = F(y) and
u = 2y-z
We have
‖ ‖ = ‖ ( ) ( )‖ = ‖ ( ) ( ( ))‖](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-1-320.jpg)
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≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3max [P, Q]
P =
‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖
‖ ‖
and Q =
‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖
‖ ‖
Case 1: when max [P, Q] = P
Then ‖ ‖
≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3[
‖ ( )‖‖ ( ) ( )‖ ‖ ( )‖‖ ( ) ( )‖
‖ ( )‖
]
= a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )‖ + a3[
‖ ( )‖‖ ( ) ‖ ‖ ‖‖ ( ) ( )‖
‖ ( )‖
]
= a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )( ) ( )‖ + a3[
‖ ( )‖‖ ( ) ‖ ‖ ( )( ) ‖‖ ( ) ( )‖
‖ ( )( ) ( )‖
]
= a1 [‖ ( )‖ ‖ ( ) ‖ + ‖ ( )‖ + 2a3 ‖ ( )‖ + a3 ‖ ( ) ( )‖
= a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 3a3 ‖ ( )‖ +a3 ‖ ( ) ‖
= a1[‖ ( )‖ + ‖ ( )‖] + ‖ ( )‖
= (a1 + 3 ) [ ‖ ( )‖ + ( ) ‖ ( )‖
Therefore ,
‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖
Also
‖ ‖ = ‖ ‖ = ‖( )( ) ( ) ‖ = ‖ ( ) ( )‖
≤ a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ‖ + a3[
‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )‖
‖ ‖
]
= a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ( )( )‖
+ a3[
‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )( ) ( )‖
‖ ( )( )‖
]
= a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 2a3 ‖ ( )‖ + a3 ‖ ‖
+ a3 ‖ ( )‖
= (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ .
Therefore,
‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ . ……. (1.3)
Now
‖ ‖≤ ‖ ‖ + ‖ ‖
= (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ + (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖
( )‖](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-2-320.jpg)
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= 2(a1 + 3a3)[ ‖ ( )‖ + 2( ) ‖ ( )‖
Thus, ‖ ‖ 2(a1 + 3a3) [ ‖ ( )‖ + 2( ) ‖ ( )‖ ……. (1.4)
Also,‖ ‖ ‖ ( ) ( )‖
=‖ ( ) ‖
= 2‖ ( ) ‖
Combining (1.3) and (1.4), we have
‖ ( )‖ [( +3a3) ‖ ( )‖ + (a1 + a2/2 + /2) ‖ ( )‖ ]
Therefore ‖ ( )‖ ‖ ( )‖
Where
q=
( )
( )
since 4a1 + a2 +7a3 < 2
on taking
G = ( ) X
‖ ( ) ( )‖ ‖ ( ) ‖
= ‖ ( )‖
< ⁄ ‖ ( )‖
By the definition of q, we claim that {Gn
(x)} is a Cauchy sequence in X. Therefore, by the property of
completeness, Gn
(x)} converges to some element in X.
i.e. ( ) = x0
Which implies G( x0 ) = x0
Hence F(x0) = x0
i.e. x0 is a fixed point of F.
For the uniqueness, if possible let y0 (≠ x0) be another fixed point of F. Then
‖ ‖= ‖ ( ) ( )‖
≤ a1 [ ‖ – ( )‖ + ‖ – ( ) ‖ ] + a2 ‖ – ‖
+ a3
‖ ( )‖ ‖ ( )‖ ‖ ( )‖‖ ( )‖
‖ ‖
=a2‖ ‖ + a3
‖ ( )‖‖ ( )‖
‖ ‖
= (a2+a3)‖ ‖
Since a2 +a3 < 1 ,therefore
ǁx0 - y0‖ = 0
Hence x0 = y0 .
Case 2: when max [P, Q] = Q
Then ‖ ‖
≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3[
‖ ( )‖‖ ( )‖ ‖ ( ) ( )‖‖ ( ) ( )‖
‖ ( )‖
]
= a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )‖ + a3[
‖ ( )‖‖ ‖ ‖ ( ) ‖‖ ( ) ( )‖
‖ ( )‖
]](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-3-320.jpg)
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= a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )( ) ( )‖ + a3[
‖ ( )‖‖ ( )( ) ‖ ‖ ( ) ‖‖ ( ) ( )‖
‖ ( )( ) ( )‖
]
= a1 [‖ ( )‖ ‖ ( ) ‖ + ‖ ( )‖ + a3 ‖ ( )‖ +2 a3 ‖ ( ) ( )‖
= a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + a3 ‖ ( )‖ +2a3 [ ‖ ( ) ‖+‖ ( )‖
= a1 [‖ ( )‖ +‖ ( )‖] + ‖ ( )‖+3a3‖ ( )‖+2a31/2‖ ( )‖
= (a1 + 3 ) [ ‖ ( )‖ + ( ) ‖ ( )‖
Therefore,
‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖
Also
‖ ‖ = ‖ ‖ = ‖( )( ) ( ) ‖ = ‖ ( ) ( )‖
≤ a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ‖ + a3[
‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )‖
‖ ‖
]
= a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ( )( )‖
+ a3[
‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )( ) ( )‖
‖ ( )( )‖
]
= a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 2a3‖ ‖ + a3 ‖ ( )‖
+ a3 ‖ ( )‖
= (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ .
Therefore,
‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ . ……. (1.5)
Now
‖ ‖≤ ‖ ‖ + ‖ ‖
= (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ + (a1 + 3a3)[ ‖ ( )‖ + ( )
‖ ( )‖
= 2(a1 + 3a3)[ ‖ ( )‖ + 2( ) ‖ ( )‖
Thus, ‖ ‖ 2(a1 + 3a3) [ ‖ ( )‖ + 2( ) ‖ ( )‖ ……. (1.6)
Also,‖ ‖ ‖ ( ) ( )‖
=‖ ( ) ‖
= 2‖ ( ) ‖
Combining (1.5) and (1.6), we have](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-4-320.jpg)
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‖ ( )‖ [( +3a3) ‖ ( )‖ + (a1 + a2/2 + a3) ‖ ( )‖ ]
Therefore ‖ ( )‖ ‖ ( )‖
Where
q=
( )
( )
since 4a1 + a2 +8a3 < 2
on taking
G = ( ) X
‖ ( ) ( )‖ ‖ ( ) ‖
=‖ ( )( ) ‖
= ‖ ( )‖
< ⁄ ‖ ( )‖
By the definition of q, we claim that {Gn
(x)} is a Cauchy sequence in X. Therefore, by the property of
completeness, {Gn
(x)} converges to some element in X.
i.e. ( ) = x0
Which implies G( x0 ) = x0
Hence F(x0) = x0
i.e. x0 is a fixed point of F.
For the uniqueness, if possible let y0 (≠ x0) be another fixed point of F. Then
‖ ‖= ‖ ( ) ( )‖
≤ a1 [ ‖ – ( )‖ + ‖ – ( ) ‖ ] + a2 ‖ – ‖
+ a3
‖ ( )‖ ‖ ( )‖ ‖ ( )‖‖ ( )‖
‖ ‖
=a2‖ ‖
Since a2 < 1, therefore
‖x0 - y0‖ = 0
Hence x0 = y0
References:-
[1] BROWDER F.E. Non-expansive non-linear operators in Banach space. Proc. Nat. Acad. Sci. U.S.A.
54,1041-1044,(1965).
[2] DATSON,W.G.Jr. Fixed points of quasi non-expansive mappings. J.Austral. Math. Soc.13, 167-170(1972).
[3] EMMANUELE, G. Fixed point theorems in complete metric space. Not linear Anal. 5, 287-292,(1981).
[4] GOEBEL, K. An elementary proof of the fixed theorem of Browder and Kirk. Michigan Math. J. 16, 381-
383, (1969).
[5] GOEBEL, K. AND ZLOTKIEWICZ, E. Some fixed point theorems in Banach spaces. Collq. Math. 23,
103-106,(1971).
[6] GOHDE Zum prizip dev kontraktiven abbildung. Math.Nachr. 30, 251-258, (1965).
[7] ISEKI,K. Fixed point theorem in Banach spaces, Math. Sem. Notes Kobe Univ. vol.2(1), paper no.3,4 pp,
(1974).](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-5-320.jpg)
![Mathematical Theory and Modeling www.iiste.org
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[8] JAIN, R.K. AND JAIN, R. A result on fixed points in Banach Space. Acta Indica. vol. XVM No.3, 294-
297(1989)
[9] KHAN, M.S. Fixed point and their approximation in Banach spaces for certain commuting mappings.
Glasgow Math, Journal 23, (1982).
[10] KIRK,W.A. Fixed point theorem for non-expansive mapping-II contemp. Math. 18, 121-140,(1983).
[11] SHARMA, PL AND RAJPUT, SS. Fixed point theorems in Banach space. Vikram math. Jour. vol.4,
35,(1983).
[12] SHARMA,PL AND BAJAJ, N. Fixed point theorem in Banach Space for commuting mappings. Jour. of
MACT vol.16, 11-13, (1983).
[13] SINGH, M.R. AND CHATTERJEE. Fixed point theorems in Banach space. Pure Math. Manu.vol.6,
53-61,(1987).](https://image.slidesharecdn.com/afixedpointresultinbanachspaces-150704063014-lva1-app6891/85/A-fixed-point-result-in-banach-spaces-6-320.jpg)
A fixed point result in banach spaces
- 1. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 109 A Fixed Point Result in Banach Spaces R.K.Sharma1 , Bharti Choure2 , R.K. Bhardwaj3 1&2 Department of Mathematics,B.U.I.T Bhopal-462026,India 3 Department of Mathematics, TRUBA, Institute of engineering & IT Bhopal Email:[email protected] Abstract In the present paper we establish some fixed point theorems in Banach space taking rational expression. Our Result Generalize the result of many authors. Key words: Fixed point, common fixed point, rational expressions, Banach spaces Introduction: Fixed point has drawn the attentions of the authors working in non-linear analysis, the study of non-expansive mapping and the existence of fixed point. The non-expansive mappings include contraction as well as contractive mappings. Browder [1] was the first mathematician to study non-expansive mappings; he applied these results for proving the existence of solutions of certain integral equations. It is well known that differential and the integral equations that arise in physical problems are generally non-linear, therefore the fixed point technique provides a powerful tool for obtaining the solutions of these equations which otherwise are difficult to solve by ordinary methods. No doubt, it is also true that some qualitative properties of the solution of related equations is lost by functional analysis approach. Many attempts have been made in this direction to formulate fixed point theorems. Schauder, J. formulated the well known Schauder’s fixed point principle in 1930. Browder [1], Gohde [6] and Kirk [10] have independently proved a fixed point theorem for non-expansive mappings defined on a closed bounded and convex subset of a uniformly convex Banach space and in the spaces with richer generalizations of non-expansive mappings, prominent being Datson [2], Emmanuele [3], Goebel [4], Goebel and Zlotkienwicz [5], Iseki [7], Sharma & Rajput [11], Singh and Chatterjee [13]. They have derived valuable results with non-contraction mapping in Banach space. Our object in this chapter is to prove some fixed and common fixed point theorems using Banach space. Our results include the results of Goebel and Zlotkiewicz [5], Iseki [7], Sharma and Bajaj [12], Khan [9], Jain and Jain [8]. We shall prove:- Theorem-1 : Let F be a mapping of a Banach space x into itself. If F satisfies the following conditions; 1. F2 = I, where I is the identity mapping. ……….(1.1) 2. ‖ ( ) ( )‖ ……….(1.2) ≤ a1 [‖ ( )‖ ‖ ( )‖] + a2 [‖ ‖ + Max { } Where P = ‖ ( )‖‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ‖ For every x,y X, where 0 < a1,a2,a3 and 4a1 + a2 + 8a3 < 2, then F has a fixed point, if a2 + a3 < 1,then F has a unique fixed point. Proof: Suppose x be a point in Banach space X. Taking y = (F+I) (x) z = F(y) and u = 2y-z We have ‖ ‖ = ‖ ( ) ( )‖ = ‖ ( ) ( ( ))‖
- 2. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 110 ≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3max [P, Q] P = ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ‖ and Q = ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ( )‖ ‖ ‖ Case 1: when max [P, Q] = P Then ‖ ‖ ≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3[ ‖ ( )‖‖ ( ) ( )‖ ‖ ( )‖‖ ( ) ( )‖ ‖ ( )‖ ] = a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )‖ + a3[ ‖ ( )‖‖ ( ) ‖ ‖ ‖‖ ( ) ( )‖ ‖ ( )‖ ] = a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )( ) ( )‖ + a3[ ‖ ( )‖‖ ( ) ‖ ‖ ( )( ) ‖‖ ( ) ( )‖ ‖ ( )( ) ( )‖ ] = a1 [‖ ( )‖ ‖ ( ) ‖ + ‖ ( )‖ + 2a3 ‖ ( )‖ + a3 ‖ ( ) ( )‖ = a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 3a3 ‖ ( )‖ +a3 ‖ ( ) ‖ = a1[‖ ( )‖ + ‖ ( )‖] + ‖ ( )‖ = (a1 + 3 ) [ ‖ ( )‖ + ( ) ‖ ( )‖ Therefore , ‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ Also ‖ ‖ = ‖ ‖ = ‖( )( ) ( ) ‖ = ‖ ( ) ( )‖ ≤ a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ‖ + a3[ ‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )‖ ‖ ‖ ] = a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ( )( )‖ + a3[ ‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )( ) ( )‖ ‖ ( )( )‖ ] = a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 2a3 ‖ ( )‖ + a3 ‖ ‖ + a3 ‖ ( )‖ = (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ . Therefore, ‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ . ……. (1.3) Now ‖ ‖≤ ‖ ‖ + ‖ ‖ = (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ + (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖
- 3. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 111 = 2(a1 + 3a3)[ ‖ ( )‖ + 2( ) ‖ ( )‖ Thus, ‖ ‖ 2(a1 + 3a3) [ ‖ ( )‖ + 2( ) ‖ ( )‖ ……. (1.4) Also,‖ ‖ ‖ ( ) ( )‖ =‖ ( ) ‖ = 2‖ ( ) ‖ Combining (1.3) and (1.4), we have ‖ ( )‖ [( +3a3) ‖ ( )‖ + (a1 + a2/2 + /2) ‖ ( )‖ ] Therefore ‖ ( )‖ ‖ ( )‖ Where q= ( ) ( ) since 4a1 + a2 +7a3 < 2 on taking G = ( ) X ‖ ( ) ( )‖ ‖ ( ) ‖ = ‖ ( )‖ < ⁄ ‖ ( )‖ By the definition of q, we claim that {Gn (x)} is a Cauchy sequence in X. Therefore, by the property of completeness, Gn (x)} converges to some element in X. i.e. ( ) = x0 Which implies G( x0 ) = x0 Hence F(x0) = x0 i.e. x0 is a fixed point of F. For the uniqueness, if possible let y0 (≠ x0) be another fixed point of F. Then ‖ ‖= ‖ ( ) ( )‖ ≤ a1 [ ‖ – ( )‖ + ‖ – ( ) ‖ ] + a2 ‖ – ‖ + a3 ‖ ( )‖ ‖ ( )‖ ‖ ( )‖‖ ( )‖ ‖ ‖ =a2‖ ‖ + a3 ‖ ( )‖‖ ( )‖ ‖ ‖ = (a2+a3)‖ ‖ Since a2 +a3 < 1 ,therefore ǁx0 - y0‖ = 0 Hence x0 = y0 . Case 2: when max [P, Q] = Q Then ‖ ‖ ≤ a1 [‖ ( )‖ ‖ ( ) ( )‖ + a2 ‖ ( )‖ + a3[ ‖ ( )‖‖ ( )‖ ‖ ( ) ( )‖‖ ( ) ( )‖ ‖ ( )‖ ] = a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )‖ + a3[ ‖ ( )‖‖ ‖ ‖ ( ) ‖‖ ( ) ( )‖ ‖ ( )‖ ]
- 4. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 112 = a1 [‖ ( )‖ ‖ ( ) ‖ + a2 ‖ ( )( ) ( )‖ + a3[ ‖ ( )‖‖ ( )( ) ‖ ‖ ( ) ‖‖ ( ) ( )‖ ‖ ( )( ) ( )‖ ] = a1 [‖ ( )‖ ‖ ( ) ‖ + ‖ ( )‖ + a3 ‖ ( )‖ +2 a3 ‖ ( ) ( )‖ = a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + a3 ‖ ( )‖ +2a3 [ ‖ ( ) ‖+‖ ( )‖ = a1 [‖ ( )‖ +‖ ( )‖] + ‖ ( )‖+3a3‖ ( )‖+2a31/2‖ ( )‖ = (a1 + 3 ) [ ‖ ( )‖ + ( ) ‖ ( )‖ Therefore, ‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ Also ‖ ‖ = ‖ ‖ = ‖( )( ) ( ) ‖ = ‖ ( ) ( )‖ ≤ a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ‖ + a3[ ‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )‖ ‖ ‖ ] = a1 [‖ ( )‖ ‖ ( )‖ + a2 ‖ ( )( )‖ + a3[ ‖ ( )‖‖ ( )‖ ‖ ( )‖‖ ( )( ) ( )‖ ‖ ( )( )‖ ] = a1 [‖ ( )‖ ‖ ( )‖ + ‖ ( )‖ + 2a3‖ ‖ + a3 ‖ ( )‖ + a3 ‖ ( )‖ = (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ . Therefore, ‖ ‖ ≤ (a1 + 3a3) [ ‖ ( )‖ + ( ) ‖ ( )‖ . ……. (1.5) Now ‖ ‖≤ ‖ ‖ + ‖ ‖ = (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ + (a1 + 3a3)[ ‖ ( )‖ + ( ) ‖ ( )‖ = 2(a1 + 3a3)[ ‖ ( )‖ + 2( ) ‖ ( )‖ Thus, ‖ ‖ 2(a1 + 3a3) [ ‖ ( )‖ + 2( ) ‖ ( )‖ ……. (1.6) Also,‖ ‖ ‖ ( ) ( )‖ =‖ ( ) ‖ = 2‖ ( ) ‖ Combining (1.5) and (1.6), we have
- 5. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 113 ‖ ( )‖ [( +3a3) ‖ ( )‖ + (a1 + a2/2 + a3) ‖ ( )‖ ] Therefore ‖ ( )‖ ‖ ( )‖ Where q= ( ) ( ) since 4a1 + a2 +8a3 < 2 on taking G = ( ) X ‖ ( ) ( )‖ ‖ ( ) ‖ =‖ ( )( ) ‖ = ‖ ( )‖ < ⁄ ‖ ( )‖ By the definition of q, we claim that {Gn (x)} is a Cauchy sequence in X. Therefore, by the property of completeness, {Gn (x)} converges to some element in X. i.e. ( ) = x0 Which implies G( x0 ) = x0 Hence F(x0) = x0 i.e. x0 is a fixed point of F. For the uniqueness, if possible let y0 (≠ x0) be another fixed point of F. Then ‖ ‖= ‖ ( ) ( )‖ ≤ a1 [ ‖ – ( )‖ + ‖ – ( ) ‖ ] + a2 ‖ – ‖ + a3 ‖ ( )‖ ‖ ( )‖ ‖ ( )‖‖ ( )‖ ‖ ‖ =a2‖ ‖ Since a2 < 1, therefore ‖x0 - y0‖ = 0 Hence x0 = y0 References:- [1] BROWDER F.E. Non-expansive non-linear operators in Banach space. Proc. Nat. Acad. Sci. U.S.A. 54,1041-1044,(1965). [2] DATSON,W.G.Jr. Fixed points of quasi non-expansive mappings. J.Austral. Math. Soc.13, 167-170(1972). [3] EMMANUELE, G. Fixed point theorems in complete metric space. Not linear Anal. 5, 287-292,(1981). [4] GOEBEL, K. An elementary proof of the fixed theorem of Browder and Kirk. Michigan Math. J. 16, 381- 383, (1969). [5] GOEBEL, K. AND ZLOTKIEWICZ, E. Some fixed point theorems in Banach spaces. Collq. Math. 23, 103-106,(1971). [6] GOHDE Zum prizip dev kontraktiven abbildung. Math.Nachr. 30, 251-258, (1965). [7] ISEKI,K. Fixed point theorem in Banach spaces, Math. Sem. Notes Kobe Univ. vol.2(1), paper no.3,4 pp, (1974).
- 6. Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.4, No.1, 2014 114 [8] JAIN, R.K. AND JAIN, R. A result on fixed points in Banach Space. Acta Indica. vol. XVM No.3, 294- 297(1989) [9] KHAN, M.S. Fixed point and their approximation in Banach spaces for certain commuting mappings. Glasgow Math, Journal 23, (1982). [10] KIRK,W.A. Fixed point theorem for non-expansive mapping-II contemp. Math. 18, 121-140,(1983). [11] SHARMA, PL AND RAJPUT, SS. Fixed point theorems in Banach space. Vikram math. Jour. vol.4, 35,(1983). [12] SHARMA,PL AND BAJAJ, N. Fixed point theorem in Banach Space for commuting mappings. Jour. of MACT vol.16, 11-13, (1983). [13] SINGH, M.R. AND CHATTERJEE. Fixed point theorems in Banach space. Pure Math. Manu.vol.6, 53-61,(1987).