Some fixed point theorems in Gb-cone metric space
Komal Goyal and Bhagwati Prasad
Citation: 1802, 020004 (2017); doi: 10.1063/1.4973254
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Some Fixed Point Theorems in b
G -cone Metric Space
Komal Goyal1
and Bhagwati Prasad1,a)
1
Jaypee Institute of Information Technology, Department of Mathematics, Noida, India
a)
Corresponding author: b_prasad10@yahoo.com
Abstract.The intent of the paper is to introduce a b
G -cone metric space and study its properties. Some fixed point
theorems for the maps satisfying a general contractive condition are established in this setting. Some of the well known
existing results are obtained as special cases.
Keywords- Fixed point; G -metric space; b
G -cone metric space; Cone.
INTRODUCTION
The celebrated Banach contraction theorem (1922) is a classical and most powerful tool of nonlinear analysis
which provides a constructive approach for solving various functional equations arising out of a number of physical
problems related to diverse discipline of science and engineering. It has been extensively studied, generalized,
enriched and extended in the literature by a number of authors in various setting for a variety of single valued and
multi valued maps (see for instance [1-17], [20-32], [34] and several references thereof). For an excellent comparison
of the various contractive conditions, one may refer to Rhoades [33]. Gahlar [12] introduced 2-metric space as a
generalization of the usual notion of a metric space. However, Ha et al [14] observed that a 2-metric need not be a
continuous function and there is no relationship between them. Dhage [11] introduced a new concept of metric space
called D-metric space and subsequently developed the topological structures in this space through a series of papers.
Mustafa and Sims [25] (also see Mustafa [22] and Mustafa et al [23-24]) in their seminal papers established that the
claims made by Dhage for D-metric spaces were not correct. To overcome this, they introduced the notion of G-
metric space. On the other hand, another generalization of a metric space was introduced by Bakhtin [5] which was
studied by many authors such as Czerwik [10], Pacurar [26], Prasad et al [28-29] and Singh and Prasad [34] for the
existence and uniqueness of the fixed point of single valued and multi-valued maps.
Aghajani [3] generalized the concept of G -metric space to b
G -metric space through b-metric. Mustafa et al. [24]
obtained coupled coincidence point results for nonlinear ( , ) weakly contractive mappings in the setting of
partially ordered b
G -metric spaces. Beg et al [6-7] generalized the cone metric spaces in the form of G-cone metric
spaces and studied topological properties such as convergence and completeness of these spaces and obtained fixed
point theorems for the maps satisfying some general conditions. Huang and Zhang [17] generalized the notion of
metric space and established fixed point results for maps under various contraction conditions in an ordered Banach
space. Using these concepts, Hussain and Shah [18] obtained some results in cone b-metric space and established
some topological properties. Later on, Huang and Xu [16] obtained some interesting results for contractive maps
without the assumption of normality in cone b-metric spaces. In the present paper our intention is to introduce b
G
-cone metric spaces and study some basic properties of them. Some fixed point results in b
G -cone metric spaces are
also established. Our results extend and generalize some of the well known previous results in G -metric space.
Mathematical Sciences and its Applications
AIP Conf. Proc. 1802, 020004-1–020004-11; doi: 10.1063/1.4973254
Published by AIP Publishing. 978-0-7354-1470-9/$30.00
020004-1
PRELIMINARIES
The basic concepts and relevant results required in the sequel are given below.
Definition 1 [18, 19, 21]. Let E be a real Banach space and P a subset of E. By we denote the zero elements of E
and by int P, the interior of P. The subset P is called a cone if and only if:
( 1)C P is closed nonempty and { };P
( 2) , , , , ;
( 3) ( ) { }.
C a b R a b x y P ax by P
C P P
A partial ordering with respect to P is defined by x y iff y x P while will represent inty x P .
Definition 2 [22]. Let X be a nonempty set and :G X X X R satisfies the following properties:
( 1) ( , , ) 0G G x y z iff ;x y z
( 2) 0 ( , , )G G x y z for all , ,x y z X with ;x y
( 3) ( , , ) ( , , )G G x x y G x y z for all , ,x y z X with ;y z
( 4) ( , , ) ( , , ) ( , , ) ...G G x y z G x z y G y z x (symmetry in all variables);
( 5) ( , , ) ( , , ) ( , , )G G x y z G x a a G a y z for all , , , .x y z a X
Then, G is a generalized or G-metric and the pair (X, G) is a generalized or a G-metric space.
Definition 3 [5, 34]. Let X be a non empty set and 1s be a given real number. A function :d X X R is said
to be a b-metric iff for all , ,x y z X , the following conditions are satisfied:
( 1) ( , ) 0 iff ,
( 2) ( , ) ( , ),
( 3) ( , ) ( ( , ) ( , )).
B d x y x y
B d x y d y x
B d x z s d x y d y z
The pair ( , )X d is called a b-metric space.
Definition 4 [3]. Let X be a nonempty set and :G X X X R with the constant 1s satisfies:
( 1) ( , , ) 0bG G x y z iff ;x y z
( 2) 0 ( , , )bG G x y z for all , ,x y z X with ;x y
( 3) ( , , ) ( , , )bG G x x y G x y z for all , ,x y z X with ;y z
( 4) ( , , ) ( , , ) ( , , ) ...bG G x y z G x z y G y z x (symmetry in all variables);
( 5) ( , , ) ( ( , , ) ( , , ))bG G x y z s G x a a G a y z for all , , , .x y z a X
Then, G is called a generalized b-metric and the pair (X, G) is a generalized b-metric space or a b
G -metric space.
We extend the concept of b
G -metric space to b
G -cone metric space in the following manner.
Definition 5. Let X be a nonempty set and E a real Banach space with cone P. A vector-valued function
:G X X X E is said to be a b
G -cone metric on X if it satisfies:
( 1) ( , , ) 0bG C G x y z iff ;x y z
( 2) 0 ( , , )bG C G x y z for all , ,x y z X with ;x y
( 3) ( , , ) ( , , )bG C G x x y G x y z for all , ,x y z X with ;y z
020004-2
( 4) ( , , ) ( , , ) ( , , ) ...bG C G x y z G x z y G y z x (symmetry in all variables);
( 5) ( , , ) ( ( , , ) ( , , ))bG C G x y z s G x a a G a y z for all , , ,x y z a X and 1.s
Then, the pair (X, G) is a b
G -cone metric space. It is to be noticed that for 1,s the ordinary triangle inequality of
cone metric space holds whereas it is not true for 1.s Thus the class of b
G -cone metric spaces are effectively
larger than that of the ordinary cone metric spaces. It is remarked that every cone metric space is a b
G -cone metric
space, but the converse may not be true (see example 1).
Example 1 [3]. Let (X, G) be a G-metric space, and
*
, , , ,
p
G x y z G x y z , where 1p is a real number. Note
that
*
G is a b
G -cone metric with
1
2
p
s .
If 1 ,p
1
( ) 2
p p p p
a b a b
Thus, for each , , , ,x y z a X we obtain,
*
1
1 * *
, , , ,
( , , ( , , ))
2 (( ( , , ) ( , , ) )
2 ( , , , , )
p
p
p p p
p
G x y z G x y z
G x a a G a y z
G x a a G a y z
G x a a G a y z
Thus is a b
G -cone metric with
1
2
p
s .
Let X = R and
1
, , for all , ,
3
G x y z x y y z x z x y z R .Then,
* 2 2
1
, , , , ( )
9
G x y z G x y z x y y z x z
is a b
G -cone metric on R with 2s , but it is not a G-metric on R.
Some well known concepts of b
G -metric may be easily extended in the setting of b
G -cone metric space in the
following manner.
Definition 6. Let X be a b
G -cone metric space and { }n
x a sequence in X. Then,
(i) The sequence { }n
x is a b
G -Cauchy sequence if, for every withc E c , there is a natural number 0
n such
that for all 0
, , , , , ,b n m l
n m l n G x x x c
(ii) The sequence { }n
x is a b
G -convergent sequence if, for every withc E c , there is an x X and an
0
n N , such that for all 0
, , ,b n
n n G x x x c for some fixed point x in X. We can say,
, , asb n
G x x x n .
Here, x is called the limit of sequence { }n
x and is denoted by lim n
n
x x .
A b
G -cone metric space on X is said to be complete if every Cauchy sequence in X is convergent in X. Sequence
{ }nx in b
G -converges to x X if and only if , ,b n m
G x x x as , .n m
Definition 7. A b
G -cone metric space is called symmetric if for all ,x y X ,
, , , , .b b
G x y y G y x x
020004-3
Proposition 1. Let (X, G) be a b
G -cone metric space, P a normal cone with normal constant K, x X and { }n
x a
sequence in X. Then,
(i) Every sequence has a unique limit point.
(ii) Every convergent sequence is Cauchy.
Proof: (i) Suppose that the limit point of any sequence { }n
x is not unique. Therefore, we have , ,b n
G x x x as
n and , ,b n
G x y y as .n
Now, from triangle inequality,
b b n n b n
G x, y, y s G x, x , x G x , y, y as n
or , ,b
G x y y as n or , which is a contradiction.
Hence proved.
(ii) Since{ }n
x is a b
G -convergent sequence then for every withc E c , there is an x X and an 0
n N ,
such that for all 0
, , ,b n
n n G x x x c we have for all 0
, ,n m l n and some fixed x X . From triangle
inequality,
, , , , , ,b n m m b n b m m
G x x x s G x x x G x x x c
or , ,b n m m
G x x x c
Therefore, every convergent sequence is Cauchy.
Proposition 2. Let X be a b
G -cone metric space. Then, the following are equivalent.
(i) The sequence { }n
x is convergent to x X .
(ii) , ,b n nG x x x as n
(iii) , ,b nG x x x as n
Proof: From Definitions 6 and 7, we have for some fixed point x in X, , , asb n
G x x x n and
, , , , , for all , .b n b n n
G x x x G x x x x y X
This shows ( ) ( )i ii .
The implications ( ) ( )ii iii and ( ) ( )iii i are obvious.
The result of Remark 2.6 in Hussain and Shah [18] is obviously true for b
G -cone metric space. It can be presented
for b
G -cone metric space as follows:
Lemma 1. Let (X, G) be a b
G -cone metric space over the ordered real Banach space E with a cone P. Then the
following properties are often used:
(i) If a b and b c, then a c.
(ii) If and , then .
(iii) If θ u c for each intc P , then u .
(iv) If intc P , θ and ,n
a then there exists 0
n such that for all 0
n n we have .
(v) If θ and ,n n
a a b b , then a b, for each cone P.
(vi) If E is a real Banach space with cone P and if a λa where a P and 0 1, then a .
020004-4
MAIN RESULT
Theorem 1. Let (X, G) be a complete symmetric b
G -cone metric space with 1. Let :s G X X X E satisfy the
following condition
, , ( , , )G Tx Ty Ty G x y y
(1)
for all , ,x y X where [0,1) is a constant. Then, T has a unique fixed point in X. Furthermore, { }
n
T x converges
to the fixed point of T in X.
Proof: Choose 0
x X and construct the sequence { }n
x such that
1
1 0
, 0
n
n n
x Tx T x n .
Then, we have, 1 1 1 1 1 1 0 0
, , , , , , , ,
n
n n n n n n n n n
G x x x G Tx Tx Tx G x x x G x x x .
For any 1, 1m p , it follows that,
1 1 1
2 2
1 1 1, 2 2 2
2
1 1 1,
, , [ , , , , ]
, , , ( , , )
, ,
m p m m m p m p m p m p m m
m p m p m p m p m p m p m p m m
m p m p m p m p
G x x x s G x x x G x x x
sG x x x s G x x x s G x x x
sG x x x s G x
3
2 2 2 3 3
1 1
2 1 1 1
, , , ..
, , , ,
m p m p m p m p m p
p p
m m m m m m
x x s G x x x
s G x x x s G x x x
1 2 2 3 3
1 0 0 1 0 0 1 0 0
1 1 1
1 0 0 1 0 0
1 2 2 3 3
, , , , , , ..
+ , , , ,
[
m p m p m p
p m p m
m p m p m p
s G x x x s G x x x s G x x x
s G x x x s G x x x
s s s
1 1 1
1 0 0 1 0 0
1 2 2 3 2 1 1
1 0 0 1 0 0
.. ] , , , ,
.. , , , ,
p m p m
m p p p p m
s G x x x s G x x x
s s s s G x x x s G x x x
11 1
1
1 0 0 1 0 01
11
1
1 0 0 1 0 0
1
1
1 0 0 1 0 0
{ 1}
[ ] , , , ,
1
{ 1}
[ ] , , , ,
, , , , .
p
m p p m
p
m p p m
p m
p m
s
s G x x x s G x x x
s
s
s G x x x s G x x x
s
s
G x x x s G x x x
s
Let c be given. Notice that
1
1
1 0 0
1 0 0
( , , ) as
( ) ( , , )
p m
p ms
s G x x x m
s G x x x
for any k.
From Lemma 1 (iv), we find 0
m N for each 0
m m such that
1
1
1 0 0 1 0 0
, , , ,
p m
p ms
G x x x s G x x x c
s
Then, for all 0
m m and any p, we have
1
1
( ) 1 0 0
1 0 0
( , , ) ( , , )
( ) ( , , )
p m
p m
m p m m
s
G x x x s G x x x c
s G x x x
.
So, by definition 6 (i), { }n
x is a Cauchy sequence in (X, G). Since (X, G) is a complete symmetric b
G -cone metric
space, there exists
*
x X such that
*
n
x x . Take 0
n N such that for each 0
n n , we have
020004-5
* * * * * *
* * *
( , , ) [ , , , , ]
[ { , , , , }]
n n n
n n n
G Tx x x s G Tx Tx Tx G Tx x x
s G x x x G x x x c
Then, by Lemma 1 (iii), we obtain
* * *
, ,G Tx x x , that is,
* *
Tx x .
For uniqueness, consider
*
y to be the other fixed point. Then,
* * * * * * * * *
, , ( , , ) , , ,G x y y G Tx Ty Ty G x y y
by Lemma 1 (vi) we have,
* *
x y .
This completes the proof.
Example 2. Let E=R, { , 0}P x R x be a cone and [0,1)X . Let :G X X X E be such that
, , , , ( , ),G x y z d x y d y z d z x
where ,d x y x y . Let :T X X be defined by, for all
4
x
Tx x X . Then,
, , , , ,
=
4 4 4 4 4 4
1
[ ]
4
, , where [0,1
G Tx Ty Tz d Tx Ty d Ty Tz d Tz Tx
Tx Ty Ty Tz Tz Tx
x y y z z x
x y y z z x
G x y z )
Hence conditions of Theorem 1 are satisfied and the point 0x is the unique fixed point of the map T.
When 1s in above, we obtain following result of Mustafa [5] in G- metric space.
Corollary 1 [22]. Let (X, G) be a complete metricG space and :T X X be a mapping satisfying the following
condition for all , ;x y X
( , , ) ( , , )G Tx Ty Ty k G x y y
where [0,1)k . Then, T has a unique fixed point in X.
Now we extend Theorem 3.1 to a more general condition.
Theorem 2. Let be a complete symmetric b
G -cone metric space with 1s and :T X X satisfies the
following condition for all ,x y X :
1 2 3 4 5
, , , , , , , , ( , , ) ( , , )G Tx Ty Ty G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y (2)
where the constant 3 51 2 4
[0,1) and for 1,2,3,4,5, 1i
i s .Then has a unique fixed point in
X. Moreover, the iterative sequence{ }
n
T x converges to the fixed point of T.
Proof: Fix 0
x X and set
1
1 0
for 0,1,2...
n
n n
x Tx T x n Firstly, we see
020004-6
1 1 1
1 2 1 1 1 3 1 1 4 1
5 1 1
1 1 1
, , ( , , )
, , , , , , , ,
( , , )
, ,
n n n n n n
n n n n n n n n n n n n
n n n
n n n
G x x x G Tx Tx Tx
G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx
G x x x
G x x x 2 1 3 4 1 1 1 5 1 1
1 1 1 2 1 4 1 4 1 1
1 4 1 1
5
2
, , , , , , ( , , )
, , ( ) , , [ , , , , ]
( ) , , (
n n n n n n n n n n n n
n n n n n n n n n n n n
n n n
G x x x G x x x G x x x G x x x
G x x x G x x x s G x x x G x x x
s G x x x 15 4
) , ,n n n
s G x x x
1 4 1 1 2 5 4 1
(1 ) , , ( ) , ,n n n n n n
s G x x x s G x x x
(3)
Secondly,
1 1 1
1 1 1 1 2 3 1 4 1 1
5 1
1 1
, , ( , , )
, , , , , , , ,
( , , )
, ,
n n n n n n
n n n n n n n n n n n n
n n n
n n n
G x x x G Tx Tx Tx
G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx
G x x x
G x x x 2 1 1 3 1 1 1 4 5 1
1 1 2 1 1 3 1 3 1 1
2 3 1 1 1
5
, , , , , , ( , , )
( , , , , [ , , , , ]
( ) , (
)
,
n n n n n n n n n n n n
n n n n n n n n n n n n
n n n
G x x x G x x x G x x x G x x x
G x x x G x x x s G x x x G x x x
s G x x x 3 15
) , ,n n n
s G x x x
2 3 1 1 1 5 3 1
(1 ) , , ( ) , ,n n n n n n
s G x x x s G x x x (4)
On adding (3) and (4), we get, 1 2 3 4
1 1 1
1 2 3 4
5
( )
, , , ,
2
2
( )
n n n n n n
s
G x x x G x x x
s
Put 1 2 5 3 4
1 2 3 4
2 ( )
2 ( )
s
s
, it is easy to see that 0 1.Thus,
1 1 1 1 0 0
, , , , , ,
n
n n n n n n
G x x x G x x x G x x x .
Following similar argument as given in Theorem 1, there exists
*
x X such that
*
n
x x .
Let c be arbitrary. Since
*
n
x x , there exists N such that
2
* * 1 2 3 4
2
2 ( )
, , for all .
2 2
n
s s s
G x x x c n N
s s
Next, we claim that
*
x is a fixed point of T. To prove
* *
Tx x . Then,
* * * * * *
* * *
1
* * * * * * *
1 2 3 4 5
( , , ) [ , , , , ]
= , , , ,
[ , , , , , , , , ( , , )]
n n n
n n n
n n n n n n n n
G Tx x x s G Tx Tx Tx G Tx x x
sG Tx Tx Tx sG x x x
s G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x x x
* *
1
* * * * * * *
1 2 1 1 3 1 1 4 5
* *
1
* * * * *
1 2
, ,
[ , , , , , , , , ( , , )]
, ,
[ , , , ,{
n
n n n n n n n n
n
n
sG x x x
s G x Tx Tx G x x x G x x x G x Tx Tx G x x x
sG x x x
s G x Tx Tx s G x x x
* * * *
1 1 3 1 1 4
* * * * * *
5 1
, , } , , , ,{
, , } ( , , )] , ,
n n n n n
n n n
G x x x G x x x s G x x x
G x Tx Tx G x x x sG x x x
020004-7
* * * 2 * * 2 * *
1 2 2 1 1 3 1 1
2 * * 2 * * * * * *
4 4 5 1
2 *
1 4
), , , , ( , , ) ( , ,
, , , , ( , , ) , ,
,
n n n n n
n n n n
s G x Tx Tx s G x x x s G x x x s G x x x
s G x x x s G x Tx Tx s G x x x sG x x x
s s G x T
* * 2 2 * * 2 *
2 4 5 2 3 1 1
, , , ( ) , ,n n n
x Tx s s s G x x x s s s G x x x
which implies that
2 * * * 2 2 * * 2 *
1 4 2 4 2 3 1 15
(1 ) ( , , ) ( ) ( , , ) ( ) ( , , ).n n n
ss s G x Tx Tx s s G x x x s s s G x x x (5)
On the other hand,
* * * * * *
* * *
* * * * * *
1 2 3
( , , ) [ , , , , ]
( , , ) ( , , )
, , [ , , , , , ,
n n n
n n n
n n n n n n
G x Tx Tx s G x Tx Tx G Tx Tx Tx
sG x Tx Tx sG Tx Tx Tx
sG x Tx Tx s G x Tx Tx G x Tx Tx G x Tx Tx
* * *
4 5
* * * * * *
1 1 1 1 1 2 3
* * *
4 1 1 5
, , ( , , )]
, , [ , , , , , ,
, , ( , , )]
n n n
n n n n n n
n n n
G x Tx Tx G x x x
sG x x x s G x x x G x Tx Tx G x Tx Tx
G x x x G x x x
* * * * * * *
1 1 1 1 1 2
* * * * * * * *
3 4 1 1 5
*
1 1
, , [ , , , , } , ,
, , , , } , , ( , , )]
, ,
{
{
n n n n n
n n n n
n n
sG x x x s s G x x x G x x x G x Tx Tx
s G x x x G x Tx Tx G x x x G x x x
sG x x x
2 * * 2 * * * *
1 1 1 1 2
2 * * 2 * * * * * *
3 3 4 1 1 5
2 * 2 * * *
1 4 1 1 2 3
, , , , , ,
, , , , , , ( , , )
, , ( ) , , (
n n n
n n n n
n n
s G x x x s G x x x s G x Tx Tx
s G x x x s G x Tx Tx s G x x x s G x x x
s s s G x x x s s G x Tx Tx s 5
2 2 * *
1 3
) , ,n
G x x xss
which implies that
2 * * * 2 * 2 2 * *
2 3 1 4 1 1 51 3
(1 ) ( , , ) ( ) ( , , ) ( ) ( , , ).n n n
s s G x Tx Tx s s s G x x x s s G x x xs (6)
On adding (5) and (6),
2 2 * * * 2 2 *
1 2 3 4 1 2 3 4 1 1
2 2 2 2 * *
1 52 3 4
(2 ) , , 2 , ,
( ) , ,2
n n
n
s s s s G x Tx Tx s s s s s G x x x
s s s s G x x xs
2 * * 2 *
1 1
( , , ( 2 ) , , .2 ) n n n
s G x x x s s G x x xs
Simple calculation ensure that
2 * * 2 *
1 1* * *
2 2
1 2 3 4
2( , , ( 2 ) , ,
, , .
(2 )
) n n n
s G x x x s s G x x x
G x Tx Tx c
s s s s
s
It is easy to see from Lemma 1 (iii), that
* * *
, , .G x Tx Tx Hence
*
x is a fixed point of T.
Finally, we show the uniqueness of fixed point. Indeed, if there is another fixed point
*
y , then
* * * * * *
* * * * * * * * * * * * * * *
1 2 3 4 5
* * * * * * * * * * * * * * *
3 4 5
, , , ,
, , , , , , , , ( , , )
[ , , , , ] [ , , , , ] ( , , )
G x y y G Tx Ty Ty
G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y
s G x y y G y Ty Ty s G y x x G x Tx Tx G x y y
* * *
3 4 5
( ) , , .s s G x y y
020004-8
Owing to 3 54
0 ( ) 1s s , we deduce from Lemma 1 (vi) that
* *
x y . This completes the proof.
Example 3. Let E=R, { , 0}P x R x be a cone. Let [0,1)X and :G X X X E be such that
, , max{ , , , , , } where ,G x y z d x y d y z d z x d x y x y . Let :T X X be defined
for all
9
x
Tx x X .
, , max , , , , , ,
1
, , max , , , , , ,
9
8
, , max , , , , , ,
9 9
8
, , max , , , , , ,
9 9
, , max
G x y y d x y d y y d y x d x y x y
G Tx Ty Ty d Tx Ty d Ty Ty d Ty Tx d Tx Ty Tx Ty x y
x
G x Tx Tx d x Tx d Tx Tx d Tx x d x Tx x Tx x x
y
G y Ty Ty d y Ty d Ty Ty d Ty y d y Ty y Ty y y
G x Ty Ty d x, , , , , ,
9
, , max , , , , , ,
9
y
Ty d Ty Ty d Ty x d x Ty x Ty x
x
G y Tx Tx d y Tx d Tx Tx d Tx y d y Tx y Tx y
So, we get, 51 2 3 4
, , , , , , , , ( , , ) , , ,G Tx Ty Ty G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y
for ,x y X , where the constant 1 52 3 4
[0,1) and , 1,2,3,4,5, 1.i
i s
Hence Theorem 2 is verified and the unique fixed point of T is ‘0’.
On putting 1s in Theorem 2, we get the following result [13].
Corollary 2 [13]. Let X be a complete symmetric G-cone metric space and :T X X satisfies the following
conditions:
1 2 3 4 5
1 2 3 4 5
( ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , )
( ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , )
i G Tx Ty Ty a G x y y a G x Tx Tx a G y Tx Tx a G x Ty Ty a G y Ty Ty
ii G Ty Tx Tx a G y x x a G y Ty Ty a G y Tx Tx a G x Ty Ty a G x Tx Tx
for all 1 2 3 4 5
, and 1x y X a a a a a . Then T has unique fixed point.
Further, when we put 51 2 3 4
0 nda, 1sa in Theorem 2, we get following result of Mustafa et
al. [23].
Corollary 3 [23]. Let (X, G) be a complete G-metric space, and :T X X ,
, , , , , ,
or , , , , , ,
G Tx Ty Ty a G x Ty Ty G y Tx Tx
G Tx Ty Ty a G x x Ty G y y Tx
for all ,x y X , with
1
0,
2
a . Then T has a unique fixed point.
REFERENCES
1. M. Abbas, M.T. Nazir and I. Beg, “Fixed point results in generalized metric spaces,” Acta Universitatis
Apulensis 2011, 215-232 (2011).
020004-9
2. M. Abbas, T. Nazir and B. Rhoades, "Common fixed point results for three maps in G-metric spaces,"
Filomat 25, 1-17 (2011).
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in partially ordered b-metric spaces," Mathematica Slovaca 64, 941-960 (2014).
4. H. Aydi,N. Bilgili and E. Karapmar, "Common fixed point results from quasi-metric spaces to G-metric
spaces," Journal of the Egyptian Mathematical Society 23, 356-361 (2014).
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(1989).
6. I. Beg, M. Abbas and T. Nazir, "Generalized cone metric spaces," The Journal of Nonlinear Sciences and its
Applications 3, 21-31 (2010).
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in Pure Mathematics 2, 94-109 (2010).
8. M. Boriceanu, "Strict fixed point theorems for multivalued operators in b-metric spaces," Int. J. Mod. Math
4, 285-301 (2009).
9. S. H. Cho, J. S. Bae, "Common fixed point theorems for mappings satisfying property (EA) on cone metric
spaces," Mathematical and Computer Modelling 53, 945-951 (2011).
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Matematico E Fisico Universita Di Modena 46, 263-276 (1998).
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(1992).
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664-669 (1966).
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Engineering Research 2, 1006-1008 (2015).
14. K. S. Ha, Y. J. Cho and A. White, "Strictly convex and strictly 2-convex 2-normed spaces," Mathematica
Japonica 33, 375–384 (1988).
15. G. E. Hardy, T. Rogers, "A generalization of a fixed point theorem of Reich," Canad. Math. Bull. 16, 201-
206 (1973).
16. H. Huang, S. Xu, "Fixed point theorems of contractive mappings in cone b-metric spaces and applications,"
Fixed Point Theory and Applications 2013, 1-10 (2013).
17. L. G. Huang, X. Zhang, "Cone metric spaces and fixed point theorems of contractive mappings," Journal of
mathematical Analysis and Applications 332 1468-1476 (2007),.
18. N. Hussain, M. Shah, "KKM mappings in cone b-metric spaces," Computers & Mathematics with
Applications 62, 1677-1684 (2011).
19. S. Janković, Z. Kadelburg and S. Radenovic, "On cone metric spaces: a survey," Nonlinear Analysis:
Theory, Methods & Applications 74, 2591-2601 (2011).
20. R. Kannan, "Some results on fixed points," Bulletin of the Calcutta Mathematical Society 60, 71-76
(1968).
21. N. Mehmood, A. Azam, "Fixed point theorem for multivalued mappings in G-Cone metric spaces," Journal
of Inequalities and Applications 2013, 1-12 (2013).
22. Z. Mustafa, "A new structure for generalized metric spaces with applications to fixed point theory," Ph.D.
Thesis, The University of Newcastle, Australia (2005).
23. Z. Mustafa, H. Obiedat, F. Awawdeh, "Some fixed point theorem for mapping on complete G-metric
spaces," Fixed Point Theory Appl 2008, 1-12 (2008).
24. Z. Mustafa, J. R. Roshan and V. Parvaneh, "Coupled coincidence point results for-weakly contractive
mappings in partially ordered-metric spaces," Fixed Point Theory and Applications 2013, 1-21 (2013).
25. Z. Mustafa, B. Sims, "Some remarks concerning D-metric spaces," Proceedings of the International
Conferences on Fixed Point Theory and Applications 2004, 189-198 (2004).
26. M. Pacurar, "Sequences of almost contractions and fixed points in b− metric spaces," Analele Universitatii
de Vest din Timisoara 48, 125-137 (2011).
27. S. R. Patil, J. Salunke, "Expansion Mapping Theorems in G-cone Metric Spaces," Int. Journal of Math.
Analysis 6, 2147 - 2158 (2012).
28. B. Prasad, B. Singh and R. Sahni, "Some approximate fixed point theorems," Int. Journal of Math. Analysis
3, 203-210 (2009).
020004-10
29. B. Prasad, B. Singh and R. Sahni, "Common Fixed point theorems with integral inequality," Applied
Mathematical Sciences 4, 2369-2377 (2010).
30. B. Prasad, B. Singh and R. Sahni, "Some general minimax theorems in topological vector
spaces," International Conference on Advances in Modeling, Optimization and Computing 2011 (2011).
31. B. Prasad, B. Singh and R. Sahni, "Common fixed point theorems for ψ-weakly commuting maps in fuzzy
metric space," Acta et Commentationes Universitatis Tartuensis de Mathematica 17, 117-126 (2013).
32. B. Prasad, R. Sahni, "Endpoints of multivalued contraction operators," ISRN Mathematical Analysis 2013,
1-7 (2013).
33. B. E. Rhoades, "A comparison of various definitions of contractive mappings," Transactions of
the American Mathematical Society 226, 257–290 (1977),
34. S. L. Singh, B. Prasad, "Some coincidence theorems and stability of iterative procedures," Computers &
Mathematics with Applications 55, 2512-2520 (2008).
020004-11

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Some Fixed Point Theorems in b G -cone Metric Space

  • 1. Some fixed point theorems in Gb-cone metric space Komal Goyal and Bhagwati Prasad Citation: 1802, 020004 (2017); doi: 10.1063/1.4973254 View online: http://dx.doi.org/10.1063/1.4973254 View Table of Contents: http://aip.scitation.org/toc/apc/1802/1 Published by the American Institute of Physics Articles you may be interested in Shape preserving trigonometric fractal interpolation 1802, 020007020007 (2017); 10.1063/1.4973257 Equalities based on rough intuitionistic fuzzy topology 1802, 020018020018 (2017); 10.1063/1.4973268 Love wave propagation in a heterogeneous orthotropic layer under initial stress lying over an inhomogeneous half-space 1802, 020009020009 (2017); 10.1063/1.4973259 Geometrical nonlinearity of 14-node brick finite element 1802, 020003020003 (2017); 10.1063/1.4973253
  • 2. Some Fixed Point Theorems in b G -cone Metric Space Komal Goyal1 and Bhagwati Prasad1,a) 1 Jaypee Institute of Information Technology, Department of Mathematics, Noida, India a) Corresponding author: [email protected] Abstract.The intent of the paper is to introduce a b G -cone metric space and study its properties. Some fixed point theorems for the maps satisfying a general contractive condition are established in this setting. Some of the well known existing results are obtained as special cases. Keywords- Fixed point; G -metric space; b G -cone metric space; Cone. INTRODUCTION The celebrated Banach contraction theorem (1922) is a classical and most powerful tool of nonlinear analysis which provides a constructive approach for solving various functional equations arising out of a number of physical problems related to diverse discipline of science and engineering. It has been extensively studied, generalized, enriched and extended in the literature by a number of authors in various setting for a variety of single valued and multi valued maps (see for instance [1-17], [20-32], [34] and several references thereof). For an excellent comparison of the various contractive conditions, one may refer to Rhoades [33]. Gahlar [12] introduced 2-metric space as a generalization of the usual notion of a metric space. However, Ha et al [14] observed that a 2-metric need not be a continuous function and there is no relationship between them. Dhage [11] introduced a new concept of metric space called D-metric space and subsequently developed the topological structures in this space through a series of papers. Mustafa and Sims [25] (also see Mustafa [22] and Mustafa et al [23-24]) in their seminal papers established that the claims made by Dhage for D-metric spaces were not correct. To overcome this, they introduced the notion of G- metric space. On the other hand, another generalization of a metric space was introduced by Bakhtin [5] which was studied by many authors such as Czerwik [10], Pacurar [26], Prasad et al [28-29] and Singh and Prasad [34] for the existence and uniqueness of the fixed point of single valued and multi-valued maps. Aghajani [3] generalized the concept of G -metric space to b G -metric space through b-metric. Mustafa et al. [24] obtained coupled coincidence point results for nonlinear ( , ) weakly contractive mappings in the setting of partially ordered b G -metric spaces. Beg et al [6-7] generalized the cone metric spaces in the form of G-cone metric spaces and studied topological properties such as convergence and completeness of these spaces and obtained fixed point theorems for the maps satisfying some general conditions. Huang and Zhang [17] generalized the notion of metric space and established fixed point results for maps under various contraction conditions in an ordered Banach space. Using these concepts, Hussain and Shah [18] obtained some results in cone b-metric space and established some topological properties. Later on, Huang and Xu [16] obtained some interesting results for contractive maps without the assumption of normality in cone b-metric spaces. In the present paper our intention is to introduce b G -cone metric spaces and study some basic properties of them. Some fixed point results in b G -cone metric spaces are also established. Our results extend and generalize some of the well known previous results in G -metric space. Mathematical Sciences and its Applications AIP Conf. Proc. 1802, 020004-1–020004-11; doi: 10.1063/1.4973254 Published by AIP Publishing. 978-0-7354-1470-9/$30.00 020004-1
  • 3. PRELIMINARIES The basic concepts and relevant results required in the sequel are given below. Definition 1 [18, 19, 21]. Let E be a real Banach space and P a subset of E. By we denote the zero elements of E and by int P, the interior of P. The subset P is called a cone if and only if: ( 1)C P is closed nonempty and { };P ( 2) , , , , ; ( 3) ( ) { }. C a b R a b x y P ax by P C P P A partial ordering with respect to P is defined by x y iff y x P while will represent inty x P . Definition 2 [22]. Let X be a nonempty set and :G X X X R satisfies the following properties: ( 1) ( , , ) 0G G x y z iff ;x y z ( 2) 0 ( , , )G G x y z for all , ,x y z X with ;x y ( 3) ( , , ) ( , , )G G x x y G x y z for all , ,x y z X with ;y z ( 4) ( , , ) ( , , ) ( , , ) ...G G x y z G x z y G y z x (symmetry in all variables); ( 5) ( , , ) ( , , ) ( , , )G G x y z G x a a G a y z for all , , , .x y z a X Then, G is a generalized or G-metric and the pair (X, G) is a generalized or a G-metric space. Definition 3 [5, 34]. Let X be a non empty set and 1s be a given real number. A function :d X X R is said to be a b-metric iff for all , ,x y z X , the following conditions are satisfied: ( 1) ( , ) 0 iff , ( 2) ( , ) ( , ), ( 3) ( , ) ( ( , ) ( , )). B d x y x y B d x y d y x B d x z s d x y d y z The pair ( , )X d is called a b-metric space. Definition 4 [3]. Let X be a nonempty set and :G X X X R with the constant 1s satisfies: ( 1) ( , , ) 0bG G x y z iff ;x y z ( 2) 0 ( , , )bG G x y z for all , ,x y z X with ;x y ( 3) ( , , ) ( , , )bG G x x y G x y z for all , ,x y z X with ;y z ( 4) ( , , ) ( , , ) ( , , ) ...bG G x y z G x z y G y z x (symmetry in all variables); ( 5) ( , , ) ( ( , , ) ( , , ))bG G x y z s G x a a G a y z for all , , , .x y z a X Then, G is called a generalized b-metric and the pair (X, G) is a generalized b-metric space or a b G -metric space. We extend the concept of b G -metric space to b G -cone metric space in the following manner. Definition 5. Let X be a nonempty set and E a real Banach space with cone P. A vector-valued function :G X X X E is said to be a b G -cone metric on X if it satisfies: ( 1) ( , , ) 0bG C G x y z iff ;x y z ( 2) 0 ( , , )bG C G x y z for all , ,x y z X with ;x y ( 3) ( , , ) ( , , )bG C G x x y G x y z for all , ,x y z X with ;y z 020004-2
  • 4. ( 4) ( , , ) ( , , ) ( , , ) ...bG C G x y z G x z y G y z x (symmetry in all variables); ( 5) ( , , ) ( ( , , ) ( , , ))bG C G x y z s G x a a G a y z for all , , ,x y z a X and 1.s Then, the pair (X, G) is a b G -cone metric space. It is to be noticed that for 1,s the ordinary triangle inequality of cone metric space holds whereas it is not true for 1.s Thus the class of b G -cone metric spaces are effectively larger than that of the ordinary cone metric spaces. It is remarked that every cone metric space is a b G -cone metric space, but the converse may not be true (see example 1). Example 1 [3]. Let (X, G) be a G-metric space, and * , , , , p G x y z G x y z , where 1p is a real number. Note that * G is a b G -cone metric with 1 2 p s . If 1 ,p 1 ( ) 2 p p p p a b a b Thus, for each , , , ,x y z a X we obtain, * 1 1 * * , , , , ( , , ( , , )) 2 (( ( , , ) ( , , ) ) 2 ( , , , , ) p p p p p p G x y z G x y z G x a a G a y z G x a a G a y z G x a a G a y z Thus is a b G -cone metric with 1 2 p s . Let X = R and 1 , , for all , , 3 G x y z x y y z x z x y z R .Then, * 2 2 1 , , , , ( ) 9 G x y z G x y z x y y z x z is a b G -cone metric on R with 2s , but it is not a G-metric on R. Some well known concepts of b G -metric may be easily extended in the setting of b G -cone metric space in the following manner. Definition 6. Let X be a b G -cone metric space and { }n x a sequence in X. Then, (i) The sequence { }n x is a b G -Cauchy sequence if, for every withc E c , there is a natural number 0 n such that for all 0 , , , , , ,b n m l n m l n G x x x c (ii) The sequence { }n x is a b G -convergent sequence if, for every withc E c , there is an x X and an 0 n N , such that for all 0 , , ,b n n n G x x x c for some fixed point x in X. We can say, , , asb n G x x x n . Here, x is called the limit of sequence { }n x and is denoted by lim n n x x . A b G -cone metric space on X is said to be complete if every Cauchy sequence in X is convergent in X. Sequence { }nx in b G -converges to x X if and only if , ,b n m G x x x as , .n m Definition 7. A b G -cone metric space is called symmetric if for all ,x y X , , , , , .b b G x y y G y x x 020004-3
  • 5. Proposition 1. Let (X, G) be a b G -cone metric space, P a normal cone with normal constant K, x X and { }n x a sequence in X. Then, (i) Every sequence has a unique limit point. (ii) Every convergent sequence is Cauchy. Proof: (i) Suppose that the limit point of any sequence { }n x is not unique. Therefore, we have , ,b n G x x x as n and , ,b n G x y y as .n Now, from triangle inequality, b b n n b n G x, y, y s G x, x , x G x , y, y as n or , ,b G x y y as n or , which is a contradiction. Hence proved. (ii) Since{ }n x is a b G -convergent sequence then for every withc E c , there is an x X and an 0 n N , such that for all 0 , , ,b n n n G x x x c we have for all 0 , ,n m l n and some fixed x X . From triangle inequality, , , , , , ,b n m m b n b m m G x x x s G x x x G x x x c or , ,b n m m G x x x c Therefore, every convergent sequence is Cauchy. Proposition 2. Let X be a b G -cone metric space. Then, the following are equivalent. (i) The sequence { }n x is convergent to x X . (ii) , ,b n nG x x x as n (iii) , ,b nG x x x as n Proof: From Definitions 6 and 7, we have for some fixed point x in X, , , asb n G x x x n and , , , , , for all , .b n b n n G x x x G x x x x y X This shows ( ) ( )i ii . The implications ( ) ( )ii iii and ( ) ( )iii i are obvious. The result of Remark 2.6 in Hussain and Shah [18] is obviously true for b G -cone metric space. It can be presented for b G -cone metric space as follows: Lemma 1. Let (X, G) be a b G -cone metric space over the ordered real Banach space E with a cone P. Then the following properties are often used: (i) If a b and b c, then a c. (ii) If and , then . (iii) If θ u c for each intc P , then u . (iv) If intc P , θ and ,n a then there exists 0 n such that for all 0 n n we have . (v) If θ and ,n n a a b b , then a b, for each cone P. (vi) If E is a real Banach space with cone P and if a λa where a P and 0 1, then a . 020004-4
  • 6. MAIN RESULT Theorem 1. Let (X, G) be a complete symmetric b G -cone metric space with 1. Let :s G X X X E satisfy the following condition , , ( , , )G Tx Ty Ty G x y y (1) for all , ,x y X where [0,1) is a constant. Then, T has a unique fixed point in X. Furthermore, { } n T x converges to the fixed point of T in X. Proof: Choose 0 x X and construct the sequence { }n x such that 1 1 0 , 0 n n n x Tx T x n . Then, we have, 1 1 1 1 1 1 0 0 , , , , , , , , n n n n n n n n n n G x x x G Tx Tx Tx G x x x G x x x . For any 1, 1m p , it follows that, 1 1 1 2 2 1 1 1, 2 2 2 2 1 1 1, , , [ , , , , ] , , , ( , , ) , , m p m m m p m p m p m p m m m p m p m p m p m p m p m p m m m p m p m p m p G x x x s G x x x G x x x sG x x x s G x x x s G x x x sG x x x s G x 3 2 2 2 3 3 1 1 2 1 1 1 , , , .. , , , , m p m p m p m p m p p p m m m m m m x x s G x x x s G x x x s G x x x 1 2 2 3 3 1 0 0 1 0 0 1 0 0 1 1 1 1 0 0 1 0 0 1 2 2 3 3 , , , , , , .. + , , , , [ m p m p m p p m p m m p m p m p s G x x x s G x x x s G x x x s G x x x s G x x x s s s 1 1 1 1 0 0 1 0 0 1 2 2 3 2 1 1 1 0 0 1 0 0 .. ] , , , , .. , , , , p m p m m p p p p m s G x x x s G x x x s s s s G x x x s G x x x 11 1 1 1 0 0 1 0 01 11 1 1 0 0 1 0 0 1 1 1 0 0 1 0 0 { 1} [ ] , , , , 1 { 1} [ ] , , , , , , , , . p m p p m p m p p m p m p m s s G x x x s G x x x s s s G x x x s G x x x s s G x x x s G x x x s Let c be given. Notice that 1 1 1 0 0 1 0 0 ( , , ) as ( ) ( , , ) p m p ms s G x x x m s G x x x for any k. From Lemma 1 (iv), we find 0 m N for each 0 m m such that 1 1 1 0 0 1 0 0 , , , , p m p ms G x x x s G x x x c s Then, for all 0 m m and any p, we have 1 1 ( ) 1 0 0 1 0 0 ( , , ) ( , , ) ( ) ( , , ) p m p m m p m m s G x x x s G x x x c s G x x x . So, by definition 6 (i), { }n x is a Cauchy sequence in (X, G). Since (X, G) is a complete symmetric b G -cone metric space, there exists * x X such that * n x x . Take 0 n N such that for each 0 n n , we have 020004-5
  • 7. * * * * * * * * * ( , , ) [ , , , , ] [ { , , , , }] n n n n n n G Tx x x s G Tx Tx Tx G Tx x x s G x x x G x x x c Then, by Lemma 1 (iii), we obtain * * * , ,G Tx x x , that is, * * Tx x . For uniqueness, consider * y to be the other fixed point. Then, * * * * * * * * * , , ( , , ) , , ,G x y y G Tx Ty Ty G x y y by Lemma 1 (vi) we have, * * x y . This completes the proof. Example 2. Let E=R, { , 0}P x R x be a cone and [0,1)X . Let :G X X X E be such that , , , , ( , ),G x y z d x y d y z d z x where ,d x y x y . Let :T X X be defined by, for all 4 x Tx x X . Then, , , , , , = 4 4 4 4 4 4 1 [ ] 4 , , where [0,1 G Tx Ty Tz d Tx Ty d Ty Tz d Tz Tx Tx Ty Ty Tz Tz Tx x y y z z x x y y z z x G x y z ) Hence conditions of Theorem 1 are satisfied and the point 0x is the unique fixed point of the map T. When 1s in above, we obtain following result of Mustafa [5] in G- metric space. Corollary 1 [22]. Let (X, G) be a complete metricG space and :T X X be a mapping satisfying the following condition for all , ;x y X ( , , ) ( , , )G Tx Ty Ty k G x y y where [0,1)k . Then, T has a unique fixed point in X. Now we extend Theorem 3.1 to a more general condition. Theorem 2. Let be a complete symmetric b G -cone metric space with 1s and :T X X satisfies the following condition for all ,x y X : 1 2 3 4 5 , , , , , , , , ( , , ) ( , , )G Tx Ty Ty G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y (2) where the constant 3 51 2 4 [0,1) and for 1,2,3,4,5, 1i i s .Then has a unique fixed point in X. Moreover, the iterative sequence{ } n T x converges to the fixed point of T. Proof: Fix 0 x X and set 1 1 0 for 0,1,2... n n n x Tx T x n Firstly, we see 020004-6
  • 8. 1 1 1 1 2 1 1 1 3 1 1 4 1 5 1 1 1 1 1 , , ( , , ) , , , , , , , , ( , , ) , , n n n n n n n n n n n n n n n n n n n n n n n n G x x x G Tx Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x x x G x x x 2 1 3 4 1 1 1 5 1 1 1 1 1 2 1 4 1 4 1 1 1 4 1 1 5 2 , , , , , , ( , , ) , , ( ) , , [ , , , , ] ( ) , , ( n n n n n n n n n n n n n n n n n n n n n n n n n n n G x x x G x x x G x x x G x x x G x x x G x x x s G x x x G x x x s G x x x 15 4 ) , ,n n n s G x x x 1 4 1 1 2 5 4 1 (1 ) , , ( ) , ,n n n n n n s G x x x s G x x x (3) Secondly, 1 1 1 1 1 1 1 2 3 1 4 1 1 5 1 1 1 , , ( , , ) , , , , , , , , ( , , ) , , n n n n n n n n n n n n n n n n n n n n n n n n G x x x G Tx Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x x x G x x x 2 1 1 3 1 1 1 4 5 1 1 1 2 1 1 3 1 3 1 1 2 3 1 1 1 5 , , , , , , ( , , ) ( , , , , [ , , , , ] ( ) , ( ) , n n n n n n n n n n n n n n n n n n n n n n n n n n n G x x x G x x x G x x x G x x x G x x x G x x x s G x x x G x x x s G x x x 3 15 ) , ,n n n s G x x x 2 3 1 1 1 5 3 1 (1 ) , , ( ) , ,n n n n n n s G x x x s G x x x (4) On adding (3) and (4), we get, 1 2 3 4 1 1 1 1 2 3 4 5 ( ) , , , , 2 2 ( ) n n n n n n s G x x x G x x x s Put 1 2 5 3 4 1 2 3 4 2 ( ) 2 ( ) s s , it is easy to see that 0 1.Thus, 1 1 1 1 0 0 , , , , , , n n n n n n n G x x x G x x x G x x x . Following similar argument as given in Theorem 1, there exists * x X such that * n x x . Let c be arbitrary. Since * n x x , there exists N such that 2 * * 1 2 3 4 2 2 ( ) , , for all . 2 2 n s s s G x x x c n N s s Next, we claim that * x is a fixed point of T. To prove * * Tx x . Then, * * * * * * * * * 1 * * * * * * * 1 2 3 4 5 ( , , ) [ , , , , ] = , , , , [ , , , , , , , , ( , , )] n n n n n n n n n n n n n n G Tx x x s G Tx Tx Tx G Tx x x sG Tx Tx Tx sG x x x s G x Tx Tx G x Tx Tx G x Tx Tx G x Tx Tx G x x x * * 1 * * * * * * * 1 2 1 1 3 1 1 4 5 * * 1 * * * * * 1 2 , , [ , , , , , , , , ( , , )] , , [ , , , ,{ n n n n n n n n n n n sG x x x s G x Tx Tx G x x x G x x x G x Tx Tx G x x x sG x x x s G x Tx Tx s G x x x * * * * 1 1 3 1 1 4 * * * * * * 5 1 , , } , , , ,{ , , } ( , , )] , , n n n n n n n n G x x x G x x x s G x x x G x Tx Tx G x x x sG x x x 020004-7
  • 9. * * * 2 * * 2 * * 1 2 2 1 1 3 1 1 2 * * 2 * * * * * * 4 4 5 1 2 * 1 4 ), , , , ( , , ) ( , , , , , , ( , , ) , , , n n n n n n n n n s G x Tx Tx s G x x x s G x x x s G x x x s G x x x s G x Tx Tx s G x x x sG x x x s s G x T * * 2 2 * * 2 * 2 4 5 2 3 1 1 , , , ( ) , ,n n n x Tx s s s G x x x s s s G x x x which implies that 2 * * * 2 2 * * 2 * 1 4 2 4 2 3 1 15 (1 ) ( , , ) ( ) ( , , ) ( ) ( , , ).n n n ss s G x Tx Tx s s G x x x s s s G x x x (5) On the other hand, * * * * * * * * * * * * * * * 1 2 3 ( , , ) [ , , , , ] ( , , ) ( , , ) , , [ , , , , , , n n n n n n n n n n n n G x Tx Tx s G x Tx Tx G Tx Tx Tx sG x Tx Tx sG Tx Tx Tx sG x Tx Tx s G x Tx Tx G x Tx Tx G x Tx Tx * * * 4 5 * * * * * * 1 1 1 1 1 2 3 * * * 4 1 1 5 , , ( , , )] , , [ , , , , , , , , ( , , )] n n n n n n n n n n n n G x Tx Tx G x x x sG x x x s G x x x G x Tx Tx G x Tx Tx G x x x G x x x * * * * * * * 1 1 1 1 1 2 * * * * * * * * 3 4 1 1 5 * 1 1 , , [ , , , , } , , , , , , } , , ( , , )] , , { { n n n n n n n n n n n sG x x x s s G x x x G x x x G x Tx Tx s G x x x G x Tx Tx G x x x G x x x sG x x x 2 * * 2 * * * * 1 1 1 1 2 2 * * 2 * * * * * * 3 3 4 1 1 5 2 * 2 * * * 1 4 1 1 2 3 , , , , , , , , , , , , ( , , ) , , ( ) , , ( n n n n n n n n n s G x x x s G x x x s G x Tx Tx s G x x x s G x Tx Tx s G x x x s G x x x s s s G x x x s s G x Tx Tx s 5 2 2 * * 1 3 ) , ,n G x x xss which implies that 2 * * * 2 * 2 2 * * 2 3 1 4 1 1 51 3 (1 ) ( , , ) ( ) ( , , ) ( ) ( , , ).n n n s s G x Tx Tx s s s G x x x s s G x x xs (6) On adding (5) and (6), 2 2 * * * 2 2 * 1 2 3 4 1 2 3 4 1 1 2 2 2 2 * * 1 52 3 4 (2 ) , , 2 , , ( ) , ,2 n n n s s s s G x Tx Tx s s s s s G x x x s s s s G x x xs 2 * * 2 * 1 1 ( , , ( 2 ) , , .2 ) n n n s G x x x s s G x x xs Simple calculation ensure that 2 * * 2 * 1 1* * * 2 2 1 2 3 4 2( , , ( 2 ) , , , , . (2 ) ) n n n s G x x x s s G x x x G x Tx Tx c s s s s s It is easy to see from Lemma 1 (iii), that * * * , , .G x Tx Tx Hence * x is a fixed point of T. Finally, we show the uniqueness of fixed point. Indeed, if there is another fixed point * y , then * * * * * * * * * * * * * * * * * * * * * 1 2 3 4 5 * * * * * * * * * * * * * * * 3 4 5 , , , , , , , , , , , , ( , , ) [ , , , , ] [ , , , , ] ( , , ) G x y y G Tx Ty Ty G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y s G x y y G y Ty Ty s G y x x G x Tx Tx G x y y * * * 3 4 5 ( ) , , .s s G x y y 020004-8
  • 10. Owing to 3 54 0 ( ) 1s s , we deduce from Lemma 1 (vi) that * * x y . This completes the proof. Example 3. Let E=R, { , 0}P x R x be a cone. Let [0,1)X and :G X X X E be such that , , max{ , , , , , } where ,G x y z d x y d y z d z x d x y x y . Let :T X X be defined for all 9 x Tx x X . , , max , , , , , , 1 , , max , , , , , , 9 8 , , max , , , , , , 9 9 8 , , max , , , , , , 9 9 , , max G x y y d x y d y y d y x d x y x y G Tx Ty Ty d Tx Ty d Ty Ty d Ty Tx d Tx Ty Tx Ty x y x G x Tx Tx d x Tx d Tx Tx d Tx x d x Tx x Tx x x y G y Ty Ty d y Ty d Ty Ty d Ty y d y Ty y Ty y y G x Ty Ty d x, , , , , , 9 , , max , , , , , , 9 y Ty d Ty Ty d Ty x d x Ty x Ty x x G y Tx Tx d y Tx d Tx Tx d Tx y d y Tx y Tx y So, we get, 51 2 3 4 , , , , , , , , ( , , ) , , ,G Tx Ty Ty G x Tx Tx G y Ty Ty G x Ty Ty G y Tx Tx G x y y for ,x y X , where the constant 1 52 3 4 [0,1) and , 1,2,3,4,5, 1.i i s Hence Theorem 2 is verified and the unique fixed point of T is ‘0’. On putting 1s in Theorem 2, we get the following result [13]. Corollary 2 [13]. Let X be a complete symmetric G-cone metric space and :T X X satisfies the following conditions: 1 2 3 4 5 1 2 3 4 5 ( ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) ( , , ) i G Tx Ty Ty a G x y y a G x Tx Tx a G y Tx Tx a G x Ty Ty a G y Ty Ty ii G Ty Tx Tx a G y x x a G y Ty Ty a G y Tx Tx a G x Ty Ty a G x Tx Tx for all 1 2 3 4 5 , and 1x y X a a a a a . Then T has unique fixed point. Further, when we put 51 2 3 4 0 nda, 1sa in Theorem 2, we get following result of Mustafa et al. [23]. Corollary 3 [23]. Let (X, G) be a complete G-metric space, and :T X X , , , , , , , or , , , , , , G Tx Ty Ty a G x Ty Ty G y Tx Tx G Tx Ty Ty a G x x Ty G y y Tx for all ,x y X , with 1 0, 2 a . Then T has a unique fixed point. REFERENCES 1. M. Abbas, M.T. Nazir and I. Beg, “Fixed point results in generalized metric spaces,” Acta Universitatis Apulensis 2011, 215-232 (2011). 020004-9
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