Fixed Point Theorems in 2- Metric Space with Continuous Convex Structure

Transcription

1 Vol6, No2, 2016 wwwiisteorg Fixed Point Theorems in 2- Metric Space with Continuous Convex Structure Nidhi Gargav 1*, Geeta Modi 2, Rizwana Jama 1 Department of Mathematics, Saifia Science PG College Bhopal Professor & Head, Department of Mathematics, Govt MVM Bhopal Abstract In the present paper fixed point theorems are proved for 2- metric spaces with continous convex structure for more generalized conditions AMS Mathematics Subject Classification (1991): 47H10, 54H25 Key words and phrases: convex metric space, fixed points 1 Introduction & Preliminaries: Since Banach s fixed point theorem in 1922, because of its simplicity and usefulness, it has become a very popular tool in solving the existence problems in many branches of nonlinear analysis For some more results of the generalization of this principle Theorem 1A: Banach [1] The well known Banach contraction principle states that If X is complete metric space and T is a contraction mapping on X into itself, then T has unique fixed point in X Theorem 1 B: Kanan [16] proved that If T is self mapping of a complete metric space X into itself satisfying: Theorem 1C: Fisher [9] proved the result with Then T has unique fixed point in X Then T has unique fixed point in X Theorem 1D: A similar conclusion was also obtained by Chaterjee [3] Theorem 1E: Ciric [5] proved the result Then T has unique fixed point in X Theorem 1F: Reich [22] proved the result Then T has unique fixed point in X Then T has unique fixed point in X Theorem1 G: In 1977, the mathematician Jaggi [14] introduced the rational expression first for all and Then T has unique fixed point in X Theorem1H: In 1980 the mathematicians Jaggi and Das [15] obtained some fixed point theorems with the mapping satisfying: 24

2 Vol6, No2, 2016 wwwiisteorg for all and Then T has unique fixed point in X These are extensions of Banach contraction principle [1] in terms of a new symmetric rational expression Takahashi [30] has introduced the definition for convexity in metric space and generalized some fixed point theorems previously proved for the Banach space Subsequently, Mochado [28], Tallman [31], Naimpally and Singh [29], Guay and Singh [26], Hadzic and Gajic [27] were among others who obtained results in this setting This paper is a continuation of the investigation in the same setting in form of Altering distance function motivated by Sharma and Devangan [23], Sharma, Sharma, Iskey [24] To prove the main result we need following modified definitions: Definition21 Let be a 2-metric space and be the closed unit interval A mapping is said to be a convex structure on if for all, a > 0, for all The metric space together with a convex structure is called the Takahashi convex metric space Any subset of a Banach space is a Takahashi convex metric space with Definition 22 Let be a convex 2-metric space A nonempty subset of is said to be convex if and only if whenever Takahashi [5] has shown that the open and closed balls are convex and that an arbitrary intersection of convex sets is also convex For an arbitrary let (1) It is easy to see that is a mapping with the properties: (i) for, (ii), for, (iii), for any Using this notation we can see that is convex iff Definition23 A convex 2-metric space will be said to have property iff every bounded decreasing set of nonempty closed convex subset of has nonempty intersection Definition 24 Let be a convex 2-metric space and be a nonempty closed, convex bounded set in For, a > 0 let us set And We thus define to be the centre of We denote the diameter of a subset of by Definition2 5 A point is a diametral point of iff Definition26 A convex 2-metric space is said to have normal structure iff for each closed bounded, convex subset of, containing at least two points, there exists, which is not a diametral point of Remarks Any compact convex 2-metric space has a normal structure Definition 27 Convex hull of the set is the intersection of all convex sets in containing, an is denoted by convex It is obvious that if is a convex set, then If we set for any Then the sequence will be increasing and lim exists, and lim In 1984, MS Khan, M Swalech and SSessa [19] expanded the research of the metric fixed point theory to a 25

3 Vol6, No2, 2016 wwwiisteorg new category by introducing a control function which they called an altering distance function Motivated by them we find the same for 2- metric spaces as follows Definition 28 ([19]) A function : Â Â is called an altering distance function if the following properties are satisfied: ( y ) y ( t) = 0Û t= 0 1 ( y ) 2 ( y ) 3 y + + y is monotonically non-decreasing y is continuous By y we denote the set of the all altering distance functions Theorem29 ( [49] ) Let ( M, d ) be a complete 2-metric space, let yîy and let : mapping a > 0 which satisfies the following inequality S M M be a For all x, yîm and for some 0< a< 1 Then S has a unique fixed point z0îm and moreover for each xî M lim S n x= z n 0 Lemma 210Let ( M, d) be 2- metric space Let { x } be a sequence in M such that n If { x n } is not a Cauchy sequence in M, then there exist an e 0 > 0 and sequences of integers positive { m( k)} and{ n( k )} with m( k) > n( k) > k Such that (i) (ii) (iii) Remark 211 It is easy to get, Definition (212) A 2- metric space is a space X in which for each triple of points x, y, z, there exists a real function d (x,y,z,) such that [M 1 ] to each pair of distinct points x,y,z, d (x,y,z) ¹ 0 [M 2 ] d (x,y,z) = 0 when at lest two of x,y,z are equal [M 3 ] d (x,y,z) = d (y,z,x) = d (x,z,y) [M 4 ] d (x,y,z) d (x,y,v) + d (x,v,z) + d (v,y,z) for all x,y,z, v in X Definition (213): A sequence {x n } in a 2-metic space (X,d) is said to be convergent at x if limit d (x n, x, z) = 0 for all z in X n Definition (214) A sequence {x n } in a 2-metric space, (x, d) is said to be Cauchy sequence if limit d (x n, x, z) = 0 for all z in X m,n Definition (215) A 2-metic space (X, d) is said to be complete if every Cauchy sequence in X is convergent Also, we need the following propositions: Proposition 1[23] Let be a convex 2- metric space Then (2) 26

4 Vol6, No2, 2016 wwwiisteorg In the remaining part of this paper Proposition 2 [ 23] For any subset 3 Main result of will denote a convex 2-metric space Now we prove the following Theorem 31 Let a function : Â Â is an altering distance function y + + be 2- metric space with continuous convex structure and let be a closed convex bounded subset of with normal structure and property If is a continuous mapping such that for, a > 0 (3) Then has a fixed point Proof Let be a family of non-empty closed convex subsets so that, then is non-empty since We partially order by inclusion, and let be the decreasing chain in Then by Property we have that So, Therefore, any chain in has a greatest lower bound, and by Zorn s Lemma there is a minimal member in We claim that is a singleton set If not, then, as shown by Takahashi [5], the centre of, denoted by, is a non-empty proper closed convex subset of Now, it is easy to see that Now, let us define a sequence and Clearly, Thus we shall prove by induction that (4), for any For (5) is valid Suppose that it is valid for then we show that it is also valid for By definition of for any sequence there exist, so that Then, by proposition 2 we have three cases: (i) (ii) (iii) Considering the first case it is clear that So, let us see the second one For any thus we have (5) We assume that (6) is valid for and prove that it is valid for For any, by preposition 1, for some Then (6), For, (I-finiter set), and for In (7) is sufficient to look only for the case wthen Further, we have 27

5 Vol6, No2, 2016 wwwiisteorg Where we suppose for for that that Now, using the hypothesis, one can see that Since by induction, similarly, we have for and Therefore, and Fixed point theorem in convex metric space After not more than for steps we shall that, And Since is the centre we have that, Which implies that for all Similarly, we can prove that for all So, in the second case we have 28

6 Vol6, No2, 2016 wwwiisteorg,for, And consequently Using (4) it is easy to prove this inequality for case (iii) Thus, for all Let us define is non-empty So, is non-empty too Since is a closed proper subset of Moreover, is continuous and that closure of convex set is convex Since mapping is continuous so, And therefore is a subset of, which is a contradiction to the minimality of Hence, consists of a single element which is a fixed point for References 1 Banach, S Surles operation dans les ensembles abstraits et leur application aux equations integrals Fund Math 3(1922) Bhardwaj, RK, Rajput, SS and Yadava, RN Application of fixed point theory in metric spaces Thai Journal of Mathematics 5 (2007) Chatterjee, SK Fixed point theorems compactes Rend Acad Bulgare Sci, 25 (1972) Choudhary, S Wadhwa, K and Bhardwaj R K A fixed point theorem for continuous function Vijnana Parishad Anushandhan Patrika(2007) Ciric, L B A generalization of Banach contraction Principle Proc Amer Math Soc 25 (1974) Chu, SCand Diag, JB Remarks on generalization on Banach principle of contractive mapping JMathArabAppli11 (1965) Das, BK and Gupta, S An extension of Banach contraction principle through rational expression Indian Journal of Pure and Applied Math6 (1975) Dubey, RP and Pathak, HK Common fixed pints of mappings satisfying rational inequalities Pure and Applied Mathematika Sciences 31 (1990) Fisher B A fixed point theorem for compact metric space PublInstMath25 (1976) Goebel, K An elementary proof of the fixed point theorem of Browder and Kirk Michigan Math J 16(1969) Iseki, K, Sharma, PL and Rajput SS An extension of Banach contraction principle through rational expression Mathematics seminar notes Kobe University 10(1982) Imdad, M and Khan TI On common fixed points of pair wise coincidently commuting non-continuous mappings satisfying a rational inequality Bull Ca Math Soc 93 (2001) Imdad, M and Khan, QH A common fixed point theorem for six mappings satisfying a rational inequality Indian J of Mathematics 44 (2002) Jaggi, DS Some unique fixed point theorems I JP Appl 8(1977) Jaggi, DS and Das, BK An extension of Banach s fixed point theorem through rational expression Bull Cal Math Soc72 (1980) Kanan, R Some results on fixed point theorems Bull Calcutta Math Soc, 60 (1969)

7 Vol6, No2, 2016 wwwiisteorg 17 Kundu, A and Tiwary, KS A common fixed point theorem for five mappings in metric spaces Review BullCal Math Soc182 (2003) Liu, Z, Feng, C and Chun, SA Fixed and periodic point theorems in 2- metric spaces Nonlinear Funct & Appl 4(2003) M S Khan, M Swalech and S Sessa, Fixed point theorems by altering distances between the points, Bull Austral Math Soc, 30 (1984) Nair, S and Shriwastava, S Common fixed point theorem for rational inequality Acta Cincia Indica 32 (2006) Naidu, SVR Fixed point theorems for self map on a 2-metric spaces Pure and Applied Mathematika Sciences 12 (1995) Reich, S Some remarks concerning contraction mapping Canada MathBull14 (1971) Sharma BK and Devangan CL Fixed point theorem in convex metric spaces Univ u Novom Sadu ZbRad Period Mat Fak Ser Mat25,1(1985), Sharma PL, Sharma BK and Iseki, K Contractive type mapping on 2-metric spaces Math Japonica 21 (1976) Singh, SL, Kumar, A and Hasim, AM Fixed points of Contractive maps Indian Journal of Mathematics 47 (2005) Guay, MD, Singh, K L, Fixed point of set valued mapping of convex metric spaces, Jnanabha 16 (1986), Hadzic, O, Gajic, Lj, Coincidence points for set valued mappings in convex metric spaces, Univ u Novom Sadu Zb Rad Prirod- Mat Fak Ser Mat 16 (1986), Machado, H Vm A characterization of convex subsets of normed spaces, Kodai Math Sem Rep 25 (1973), Naimpally, S A, Singh, K L, Fixed point and common fixed points in convex metric space, Preprint 30 Takahashi, W, A convexity in metric space and non-expansive mapping 1, Kodai Math Sem Rep 22 (1970) Tallman, L A, Fixed point for condensing multifunctions in metric space with convex structure, Kodai Math Sem Rep 29 (1979), Vajzovic, F, Fixed point theorems for nonlinear operators, Radovi Mat 1(1985), (in Russian) 33 Gajic, Lj, On convexity in convex metric spaces with applications, J Nature Phys Sci 3 (1989),