Abstract
In this paper, we consider a new extension of the Banach contraction principle, which is called the contraction inspired by the concept of contraction in -generalized metric spaces and to study the existence and uniqueness of fixed point for the mappings in metric space. Moreover, we discuss some illustrative examples to highlight the improvements that were made, and we also give an iterated application of linear integral equations.
1. Introduction
Fixed point theory is an important and fascinating subject, and it provides essential tools for solving problems arising in various branches of mathematical analysis, see [1–5]. Fixed point theory guarantees the uniqueness and existence of the solution of integral and differential equations.
In 1922, a Polish mathematician Banach introduced a contraction principle [6], which was one of the most applicable results in mathematics. In recent times, many generalizations and improvement of the Banach contraction principle have appeared in the literature (see [7–13]).
The metric function has been generalized many times by modifying the associated axioms. Specifically, Bakhtin [14] and Czerwik [15] presented -metric spaces in a way that the triangle inequality was replaced by the -triangle inequality: for all pairwise distinct points and . One of these generalizations was given by Branciari [16]. Any metric space is a generalized metric space, but in general, generalized metric space might not be a metric space for details [17, 18]. Various fixed point results have been established on such spaces; for example, Nazam et al. [19–21] have proved some fixed point and common fixed point results in partial metric and S-metric spaces. For more details, see [12, 22, 23]).
Huang and Zhang [24] redefined the concept of -metric spaces and convergence in an ordered Banach space E with a normal solid cone. Shatanawi et al. in [23] defined E-metric spaces and characterized the cone metric spaces in a more general way by defining ordered normed spaces. Also, Mehmood et al. in [25] deduced more results about -metric spaces.
Jleli et al. [11, 22] introduced the notion of -contraction and proved a fixed point theorem which generalizes the Banach contraction principle in a different way than in the known results from the literature. Later, Kari et al. [26] proved new type of fixed-point theorems in a rectangular metric space and generalized asymmetric metric space by using a modified generalized -contraction maps.
In 2014, Hussain and Salimi [27] introduced the notion of an -contraction and stated fixed point theorems for -contractions. On the other hand, Hussain et al. [28] establish some new fixed-point theorems for generalized -contractions mappings in complete -metric spaces.
In this paper, we introduce the notion of a generalized -contraction to generalize an -contraction in generalized metric space. Also, examples are given to illustrate the obtained results we derive some useful corollaries of these results.
2. Preliminaries
Definition 1 (see [16]). Let be a nonempty set and be a mapping such that for all and for all distinct points , each of them different from and (i)(ii) (iii). Then, is called a generalized metric space
Definition 2 (see [16]). Let be a generalized metric space and be a sequence in , and . Then, (i)We say that the sequence converges to if and only if (ii)We say that is the Cauchy if
Lemma 3 (see [16]). Let be a generalized metric space and be a Cauchy sequence with pairwise disjoint elements in . If converges to both and , then .
Definition 4 (see [16]). The generalized metric space is said to be complete if every Cauchy sequence in converges to an .
In [11, 22], authors defined the following collections functions. Let be the family of all functions : such that
is increasing
For each sequence is continuous.
Let be the family of all functions such that
is increasing
for each sequence there exist and such that
Definition 5. Let be a generalized metric space and be a mapping. is said to be a -contraction if there exist and such that for any where
Theorem 6 (see [11]). Let be a complete generalized metric space and let be a contraction. Then, has a unique fixed point.
Remark 7. The sets and are different.
Example 8. Define by Then, , but for any , Since , so, does not satisfy the condition , then,
Example 9 (see [29]). Define by Then, , but for any , So, does not satisfy the condition , then,
Definition 10 (see [28]). Let and :. We say that is a triangular -admissible mapping if
for all
for all
for all
for all .
Definition 11 (see [28]). Let be a generalized metric space and let : be two mappings. Then,
is a -continuous mapping on if for a given point and sequence in and for all then
is a subcontinuous mapping on , if for given point and sequence in and for all then
is a -continuous mapping on , if for given point and sequence in such that with and for all , we have
Definition 12 (see [30]). Let be a rectangular -metric space and let : be two mappings. Then, the space is said to be
-complete, if every Cauchy sequence in with for all converges in
subcomplete, if every Cauchy sequence in with for all converges in
-complete, if every Cauchy sequence in with and for all converges in
Definition 13 (see [30]). Let be a generalized metric space and let be two mappings. Then, the space is said to be
-regular, if , for all implies for all
subregular, if , for all implies for all
-regular, if , and for all imply that and for all
3. Main Results
In this section, we introduce a new notion of generalized -contraction in the context of -generalized metric spaces as follows.
Definition 14. Let denote the set of all functions satisfying the following: for all with there exists such that .
Example 15. If where , then,
Example 16. If where , then,
Definition 17. Let be a -complete generalized metric space, and let be a self-mapping on , where are two functions. We say that is an -contraction, if for all with and , we have where , and
Example 18. Let and for all . So,
Define by
Then, is a complete generalized metric space. Define by
Then, is an -continuous triangular admissible mapping.
Case 1. Since , we get Thus, which implies that Thus, Thus,
Case 2. Similarly, we conclude that Hence, is an -contraction.
Theorem 19. Let be a complete generalized metric space. Let , satisfying the following conditions: (I) is a triangular admissible mapping(II) is an contraction(III)There exists such that and (IV) is an continuousThen, has a fixed point. Moreover, has a unique fixed point when and for all fixed points
Proof. Let such that and
Define a sequence by Since is a triangular -admissible mapping, then and .
Continuing this process, we have and for all By and one has
Suppose that there exists such that Then, is a fixed point of , and we have nothing to prove. Hence, we assume that , i.e., for all We have
Indeed, suppose that for some so we have
Denote Then, (11) implies that
where
Then,
and there exists such that
Thus,
Let
Then, we have
which is a contradiction, so
Continuing this process, we get which is a contradiction. Thus, as follows, we can assume that (22) and (23) hold.
Substituting and in (11), for all , we have
where
Then,
and there exists such that
Let
Then,
It is a contradiction. Therefore,
Using , we get
Therefore, is a nonnegative strictly decreasing sequence of real numbers. Consequently, there exists such that
Now, we claim that . Arguing by contradiction, we assume that Since is a nonnegative strictly decreasing sequence of real numbers, then we have
By property of , we get
By letting in inequality (43), we obtain
It is a contradiction. Therefore,
Substituting and in (11), for all , we have
where
Since
we have
and there exists such that
Then,
Take and . Thus, one can write
By , we get
By (40), we have
which implies that
Therefore, the sequence is a nonnegative strictly decreasing sequence of real numbers. Thus, there exists such that
We assume that . By (45) and
then
Taking the in (51), and using the properties of , we obtain
Therefore,
which is a contradiction. Therefore,
Next, we shall prove that is a Cauchy sequence, i.e, for all . Suppose to the contrary, we assume that there exist and a sequence and of natural numbers such that ,
and
Now, using (40), (51), (61), and the quadrilateral inequality, we find
Then,
By quadrilateral inequality, we have
Letting in the above inequalities, we obtain
Now, by quadrilateral inequality, we have
Letting in the above inequalities, we obtain
By quadrilateral inequality, we have
Letting in the above inequalities, we obtain
By the quadrilateral inequality, we find
Letting in the above inequalities, we obtain
From (11) and by setting and , we have
Taking the limit as , we have
Applying (11) with and , we obtain
As is a continuous function
So, there exist such that . Then,
Letting in the above inequality, applying the continuity of , we have
Therefore,
which is a contradiction. Then,
Hence, is a Cauchy sequence in . By completeness of , there exists such that
Now, we show that . Arguing by contradiction, we assume that
Now, by quadrilateral inequality we get,
By letting in inequality (82) and (83), we obtain
Therefore,
Since as for all and since is an -continuous, we conclude that . Then,
So
For uniqueness, now, suppose that are two fixed points of such that . Therefore, we have
Applying (11) with and , we have
where
Therefore, we have
which implies that
which is a contradiction. Therefore, , and hence, the proof is complete.
Consequently, we have the following:
Corollary 20. Let be a complete generalized metric space, and let be two functions. Let be a self-mapping satisfying the following conditions: (i)(ii) is continuous. Then, has a unique fixed point
Proof. Define a function by
Clearly,
Taking
Thus, is an -contraction, and is a triangular admissible mapping. As in the proof of Theorem 19, has a unique fixed point .
It is clear that, if is a fixed point of , then is also a fixed point of for every . The notion of property introduced first by Jeong and Rhoades [31] that if a mapping satisfies for each , then it is said that has property or that has no periodic points.
Theorem 21. Let : be two functions, and let be an -generalized complete metric space. Let be a mapping satisfying the following conditions: (i) is a triangular -admissible mapping(ii) is an -contraction(iii) and for all . Then, has the property
Proof. Let for some fixed . As and and is a triangular -admissible mapping, then
Continuing this process, we have
for all . By and , we get
Assume that Fix , i.e.,
Applying (11) with and , we get
which implies that
Thus, there exists such that
Then,
where
As , taking the limit as Since is an increasing and contentious function, therefore,
which is a contradiction. So, Then, . Therefore, has the property ().
Assuming the following conditions, we prove that Theorem 19 still holds for not necessarily continuous.
Theorem 22. Let be two functions, and let be an complete generalized metric space.
Let be a mapping, satisfying the following assertions:
(i) is triangular admissible(ii) is contraction(iii)There exists such that and (iv) is -regularThen, has a fixed point. Moreover, has a unique fixed point whenever and for all
Proof. Let such that and . Similar to the proof of Theorem 19, we can conclude that
where From and hold for all
Suppose that for some From Theorem 19, we know that the members of the sequence are distinct. Hence, we have , i.e., for all Thus, we can apply (11), to and for all to get
Therefore,
where
Thus,
Since
Thus,
and there exist such that
If , then by (110) and the fact that and are continuous and by taking the limit as in (106), we obtain
Using (85), we get
It is a contradiction. Therefore, , that is, is a fixed point of , and so Thus, is a fixed point of The proof of the uniqueness is similar to that of Theorem 19.
Definition 23. Let be a -generalized metric space, and let be a self-mapping on . Suppose that are two functions. We say that is an -contraction, if for all with and , we have where and
Theorem 24. Let be a -complete generalized metric space, and let be two functions. Let be a self-mapping satisfying the following conditions: (i) is a triangular admissible mapping(ii) is an -contraction(iii)There exists such that and (iv)is a-continuousThen, has a fixed point. Moreover, has a unique fixed point when and for all
Proof. Let such that and . Similar to the proof of Theorem 19, we can conclude that
By , there exist and such that Suppose that . So, there exists such that
Taking , we have
Suppose now that . Let be an arbitrary positive number. So, there exists such that
Taking , we have
Thus, in all cases, there exist and such that
By induction, we obtain
Letting in the above inequality, we obtain
So, there exists such that
By , there exist and such that
Suppose that . So, there exists such that
Taking , we have
Suppose now that . Let be an arbitrary positive number. So, there exists such that
So by taking , we have
Thus, in all cases, there exist and such that
By induction, we obtain
Letting in the above inequality, we obtain
So, there exists such that
If and with , then
If and with , then
Therefore,
As , the series converges. Therefore, by taking the limit as in (136), we get
Hence, is a Cauchy sequence. Since is complete, there exists such that
Since is -continuous,
Then,
This proves that is a fixed point of .
Corollary 25. Let be a -complete generalized metric space. Let be two functions. Let be a self-mapping satisfying the following conditions: (i)(ii) is a triangular -admissible mapping(iii)There exists such that and (iv) is a continuousThen, has a fixed point. Moreover, has a unique fixed point when and for all
Proof. Define a function by So, , and is an -contraction. As in the proof of Theorem 24, has a unique fixed point .
Example 26. Let and . Define by Then, is a complete generalized metric space. Define by Then, is an -continuous triangular admissible mapping.
Case 1. Since and , we get Thus, On the other hand, which implies that Thus, As Thus,
Case 2. As and , Thus, On the other hand, which implies that Thus, As Thus, where Hence, conditions (11) and (115) are satisfied. Therefore, has a unique fixed point .
4. Application to Nonlinear Integral Equations
In this section, we endeavour to apply Theorems 19 and 24 to prove the existence and uniqueness of the integral equation of the Fredholm type.
where , , and are continuous functions and for some constant depending on the parameters and .
Theorem 27. Suppose the function is such that and . Then, the equation (160) has a unique solution and .
Proof. Let and defined by . Define given by Then, is a complete generalized metric space. Assume that and . Then, we get Thus, As and for any , then we can take natural exponential sides and get Since , which implies that Hence, for all with and . Then, satisfies conditions (11) and (115) which are hold.
5. Concluding Remarks
The paper deals with contraction in -generalized metric spaces, which is an extension of the Banach contraction principle. We prove fixed point theorems of some generalized contractions which are defined on generalized metric spaces that satisfy a -complete generalized metric space condition. Our generalized results are based on -contraction. Finally, we present an application dealing with the existence of solutions for integral equation of the Fredholm type. Further, we also need to illustrate some generalizations of the introduced contraction mappings for generalized metric spaces with a graph. Some open problems for the future, for example, fixed circle problem or fixed figure problem of the contraction mappings for generalized metric spaces.
Data Availability
No underlying data was collected.
Conflicts of Interest
The authors declare that they have no competing interests.
Authors’ Contributions
The authors equally conceived of the study, participated in its design and coordination, drafted the manuscript, participated in the sequence alignment, and read and approved the final manuscript.
Acknowledgments
The authors acknowledge with thanks the Department of Research Affairs at UAEU. This project is financially supported by UPAR-2019 (Fund No. 31S397).