In [
Citation: Amjad Ali, Muhammad Arshad, Awais Asif, Ekrem Savas, Choonkil Park, Dong Yun Shin. On multivalued maps for φ-contractions involving orbits with application[J]. AIMS Mathematics, 2021, 6(7): 7532-7554. doi: 10.3934/math.2021440
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In [
Let (ˆU,d) be a metric space. For ˆℓ∈ˆU and β1⊆ˆU, let db(ˆℓ1,β1)=inf{db(ˆℓ1,ˆℓ2):ˆℓ2∈β1}. Denote N(ˆU), CL(ˆU), CB(ˆU) by the class all nonempty subsets of ˆU, the class of all nonempty closed subsets of ˆU and the class of all nonempty closed and bounded subsets of ˆU respectively. Define the Hausdorff-Pompeiu metric ˆHb induced by db on CB(ˆU) as follows:
ˆHb(β1,β2)=max{supˆℓ1∈β1db(ˆℓ1,β2),supˆℓ2∈β2db(ˆℓ2,β1)} |
for all β1,β2∈CL(ˆU). A point ˆℓ∈ˆU is said to be a fixed point of ˜T:ˆU→CL(ˆU), if ˆℓ∈˜Tˆℓ. If, for ˆℓ0∈ˆU, there exists a sequence {ˆℓi} in ˆU such that ˆℓi∈˜Tˆℓi−1, then O(˜T,ˆℓ0)={ˆℓ0,ˆℓ1,ˆℓ2,...} is said to be an orbit of ˜T:ˆU→CL(ˆU). A mapping f:ˆU→R is said to be ˜T-orbitally lower semi-continuous (o.l.s.c) if {ˆℓi} is a sequence in O(˜T,ˆℓ0) and ˆℓi→ϱ implies f(ϱ)≤lim infif(ˆℓi).
From now on, Nadler [13] realized the following multivalued version of BCP:
Theorem 1.1. [13] Let (ˆU,db) be a complete metric space and T:ˆU→CB(ˆU) be a Nadler contraction, i.e., there is γ∈[0,1) such that
ˆHb(Tˆℓ1,Tˆℓ2)≤γdb(ˆℓ1,ˆℓ2)forallˆℓ1,ˆℓ2∈ˆU. |
Then T possesses at least one fixed point.
We start the following results for main sequel.
Lemma 1.2. [13] Let (ˆU,db) be a metric space, β2∈CB(ˆU) and ˆℓ∈ˆU. Then, for each ϵ>0, there exists ν∈β2 such that
db(ˆℓ,ν)≤db(ˆℓ,β2)+ϵ. |
Lemma 1.3. [19] Let (ˆU,db) be a metric space and β1, β2∈CB(ˆU) with ˆHb(β1,β2)>0. Then for all h>1 and ˆℓ∈β1, there exists ν=ν(ˆℓ)∈β2 such that
db(ˆℓ,ν)<hˆHb(β1,β2). |
There after, many researchers worked on existence of fixed point theorems of single valued mappings can improve in the module of multi-valued mappings that satisfying various classes of contractive mappings (see [1,2,3,4,6,9,10,12,15,17,18,19,20]).
Definition 1.4. [8] A b-metric space on a nonempty set M is a function b:ˆU׈U→R+ such that for all ˆℓ1,ˆℓ2,ˆℓ3∈ˆU and a given real number s≥1, the following conditions hold:
(bi) db(ˆℓ1,ˆℓ2)=0 if and only if ˆℓ1=ˆℓ2;
(bii) db(ˆℓ1,ˆℓ2)=db(ˆℓ2,ˆℓ1);
(biii) db(ˆℓ1,ˆℓ3)≤s[db(ˆℓ1,ˆℓ2)+db(ˆℓ2,ˆℓ3)].
The pair (ˆU,db) is known as b-metric space.
The following examples present the context of b-metric spaces, which are essentially larger than the context of metric spaces [8].
Example 1.5. [8] Let ˆU=lp(R) with p∈(0,1) where lp(R)={{ˆℓi}⊂R:+∞∑i=1|ˆℓi|p<∞}. A function b:ˆU׈U→R+ is given by b(ˆℓ1,ˆℓ2)=(+∞∑i=1|ˆℓi|p)1p, where ˆℓ1=ˆℓi and ˆℓ2=ˆℓi′. Then the pair (ˆU,db) is known as b-metric space with s=21p.
Example 1.6. [8] Let ˆU=Lp[0,1] be the space of all real valued functions ˆℓ(r), 0≤r≤1 in such a way that 1∫0|ˆℓ(r)|1pdr<∞. A function b:ˆU׈U→R+ is given by b(ˆℓ1,ˆℓ2)=(1∫0|ˆℓ1(r)−ˆℓ2(r)|p)1p. Then the pair (ˆU,db) is known as b-metric space with s=21p.
Definition 1.7. [8] A sequence {ˆℓi} in b-metric space ˆU is said to be convergent if there is ˆℓ∈ˆU such that db(ˆℓi,ˆℓ)→0 as i→+∞ and write limi→+∞(ˆℓi)=ˆℓ. A sequence {ˆℓi} in (ˆU,db) is said to be Cauchy if db(ˆℓi,ˆℓi′)→0 as i,i′→+∞. A b-metric space (ˆU,db) is said to be complete if every Cauchy sequence in ˆU converges.
Note that, in general, the b-metric is not a continuous functional. Recently, Liu et al. [12] produced the following classical function:
Definition 1.8. Let φ:(0,+∞)→(0,+∞) satisfy the following conditions:
(φa) φ is nondecreasing;
(φb) for all {ˆℓi} in (0,+∞), limi→+∞φ(ˆℓi)=0 if and only if limi→+∞(ˆℓi)=0;
(φc) φ is continuous.
From now on, we denote by φ∗ the set of all function that satisfying (φa)−(φc). The following well known two lammas of φ functions will be needed in our forthcoming sequel:
Lemma 1.9. [12] Let {ˆℓi}i be a bounded sequence of real numbers and all its convergent subsequences have the same limit γ. Then {ˆℓi}i is convergent and limi→+∞(ˆℓi)=γ.
Lemma 1.10. Let φ:(0,+∞)→(0,+∞) be a nondecreasing and continuous function with infˆℓ∈(0,+∞)φ(ˆℓ)=0 and {ˆℓi}i∈(0,+∞). Then
limi→+∞φ(ˆℓi)=0ifandonlyiflimi→+∞(ˆℓi)=0. |
Proof. (⇒) Suppose limi→+∞φ(ˆℓi)=0. Then we claim that the sequence {ˆℓi} is bounded. In fact, if the sequence is unbounded, then we may assume that ˆℓi→+∞ and so for all δ>0, there is i0∈N such that ˆℓi >δ for all i>i0. Hence φ(δ)≤φ(ˆℓi) and so φ(δ)≤limi→+∞φ(ˆℓi)=0, which contradicts to φ(δ)>0. Thus {ˆℓi} is bounded. Hence there exists a subsequence {ˆℓii}⊂{ˆℓi} such that limi→+∞{ˆℓii}=k (where k is nonnegative number). Clearly k≥0. If k>0, then there is i0∈N such that {ˆℓii}∈(k2,3k2) for all i≥i0. By (φa), we deduce that φ(k2)≤limi→+∞{ˆℓii}=0, which contradicts to φ(k2)>0. Consequently, setting k=0 and by the above lemma, we have limi→+∞(ˆℓi)=0.
(⇐) Suppose that infˆℓ∈(0,+∞)φ(ˆℓ)=0. If ˆℓi→0, then for any given ϵ>0, there is k>0 such that φ(k)∈(0,ϵ) and there exists i1∈N such that ˆℓi<k for all i>i1. Therefore, 0<φ(ˆℓi)≤φ(k)<ϵ for i>i1. Hence φ(ˆℓi)→0 as i→+∞.
Throughout this paper E denotes an interval on R+ containing 0, that is, an interval of the form [0,R], [0,R), or [0,+∞). Proinov [14] introduced the following:
Lemma 1.11. [14] Let ˆℓ0∈Λ (Λ is a closed subset of ˆU) such that
db(ˆℓ0,˜Tˆℓ0)∈E, |
and ˆℓi∈Λ for some i≥0. Then we have db(ˆℓi,˜Tˆℓi)∈E.
Definition 1.12. [14] Suppose ˆℓ0∈Λ and db(ˆℓ0,˜Tˆℓ0)∈E. Then for an iterate ˆℓi (i≥0) which belongs to Λ, we define the closed ball ¯b(ˆℓi,ρ) with center ˆℓi and radius ρ>0.
Lemma 1.13. [14] If an element ˆℓ0∈Λ satisfies db(ˆℓ0,˜Tˆℓ0)∈E and ¯b(ˆℓi,ρ)⊂Λ for some i≥0, then ˆℓi+1∈Λ and ¯b(ˆℓi+1,ρ)⊂¯b(ˆℓi,ρ).
Definition 1.14. [14] Let i≥1. A function ξ:E→E is said to be a gauge function of order i on E if it satisfies the following conditions: (a) ξ(λˆℓ)<λiξ(ˆℓ) for all λ∈(0,1) and ˆℓ∈E; (b) ξ(ˆℓ)<ˆℓ for all ˆℓ∈E−{0}.
It is easy to see that the first condition of Definition 1.14 is equivalent to the following: ξ(0)=0 and ξ(ˆℓ)/ˆℓi is nondecreasing on E−{0}.
Definition 1.15. [14] A gauge function ξ:E→E is said to be a B-GGF on E if
σ(ˆℓ)=+∞∑i=0ξi(ˆℓ)<∞,forallˆℓ∈E. |
Note that a B-GGF also satisfies the following functional equation:
σ(ˆℓ)=σ(ξ(ˆℓ))+ˆℓ. |
Proinov [14] proved his main results by assuming B-GGF ξ and the mapping T:Λ→X satisfying the contractive condition d(T(x)T2(x))≤ξ(d(x;Tx)) when the underlying space is endowed with a metric. But from now on, in the context of b-metric space for some technical dialectics, Samreen et al. [16] introduced the following class of GF.
Definition 1.16. [16] A nondecreasing function ξ:E→E is said to be a b-B-GGF on E if
σ(ˆℓ)=+∞∑i=0siξi(ˆℓ)<∞,forallˆℓ∈E |
where s is the coefficient of b-metric space. Moreover, note that a b -B-GGF also satisfies the following functional equation:
σ(ˆℓ)=sσ(ξ(ˆℓ))+ˆℓ. |
Remark 1.17. Every b-B-GGF is also a B-GGF [7] but the converse may not hold. Furthermore, in [16], Samreen et al. introduced gauge functions in a b -metric space of the form
ξ(ˆℓ)={sξ(ˆℓ)ˆℓ,ifˆℓ∈E−{0}0,ifˆℓ=0 |
where s is the coefficient of b-metric space. For instance, we refer the following simple examples of gauge functions of order i as:
(a) ξ(ˆℓ)=λˆℓs for all λ∈(0,1) is a gauge function of order 1 on ˆℓ∈E;
(b) ξ(ˆℓ)=λˆℓks (λ>0, k>0) is a gauge function of order k on E=[0,l) where l=(1λ)11−k.
In 2015, Khojasteh et al. [11] introduced the concept of simulation function as follows:
Definition 1.18. [11] A function Γ:R+×R+→R is called an SF if
(Γ1) Γ(0,0)=0;
(Γ2) Γ(ˆℓ1,ˆℓ2)<ˆℓ2−ˆℓ1 for all ˆℓ′1,ˆℓ2>0;
(Γ3) if {ˆℓ1i}, {ˆℓ2i}∈(0,+∞) such that limi→+∞ˆℓ1i=limi→+∞ˆℓ2i>0, then
lim supi→+∞Γ(ˆℓ1i,ˆℓ2i)<0. |
Due to (Γ2), we have Γ(ˆℓ1,ˆℓ1)<0 for all ˆℓ1>0. From now on, we denote by ∇ the set of all functions satisfying (Γ1)-(Γ3). Some well known examples of Γ functions presented in the existing exposition are as follows:
Example 1.19. [11] For i=1,2, let ϑi:R+→R+ be continuous functions with ϑi(ˆℓ1)=0 if and only if ˆℓ1=0. The following functions Γj:R+×R+→R (j=1,⋯,6) are in ∇:
(a) Γ1(ˆℓ1,ˆℓ2)= ϑ1(ˆℓ2)−ϑ2(ˆℓ1) for all ˆℓ1,ˆℓ2≥0, where ϑ1(ˆℓ1)≤ˆℓ1≤ϑ2(ˆℓ1) for all ˆℓ1>0;
(b) Γ6(ˆℓ1,ˆℓ2)=ˆℓ2−∫ˆℓ10ς(u)dufor allˆℓ1,ˆℓ2≥0, where ς:R+→R+ is a function such that
∫ϵ0ς(u)duexistsand∫ϵ0ς(u)du>ϵ∀ϵ>0. |
Let (ˆU,db) be a metric space, ˜T be a self mapping on ˆU and Γ∈∇. ˜T is said to be a ∇-contraction with respect to Γ, if
Γ(db(˜Tˆℓ1,˜Tˆℓ2),db(ˆℓ1,ˆℓ2))≥0,forallˆℓ1,ˆℓ2∈ˆU. |
Due to (Γ2), we have db(Tˆℓ1,Tˆℓ2)≠db(ˆℓ1,ˆℓ2) for all distinct points ˆℓ1,ˆℓ2∈ˆU. Thus T is not an isometry, whenever T is a ∇-contraction with respect to Γ. Conversely, if a ∇-contraction mapping T on a metric space possesses a fixed point, then it is necessarily unique.
In the recent year, Ali et al. [5] initiated the following definition which is a modification of the notion of α-admissible.
Definition 1.20. [5] Let (ˆU,db) be a metric space and Λ be a nonempty subset of ˆU. A mapping ˜T:Λ→CB(ˆU) is called α-admissible if there exists a function α:Λ×Λ→[0,+∞) such that
α(a,b)≥1⇒α(ˆℓ,ν)≥1, |
for all ˆℓ∈˜Ta∩Λ and ν∈˜Tb∩Λ.
In this manuscript, we prove the notion of multi-valued Suzuki (SU) type fixed point results via φξ-contraction mapping and (∇α−ξ)-contraction mapping in the module of b -metric spaces, where ξ is a b-B-GGF on an interval E with some tangible examples and certain important corollaries are adopted subsequently. Our newly proved results over recent ones chiefly due to Proinov [14] and Ali et al. [1]. As the end results of a succession, we promote our main results to prove the existence of solution for the system of integral inclusion.
In this section, motivated by the notion of multivalued Suzuki type φ -contraction, we define the notion of multivalued Suzuki type φξ-contraction as follows:
Definition 2.1. Let (ˆU,db) be a b-metric space with s≥1, Λ be a closed subset of ˆU and ξ be a b-B-GGF on an interval E. A mapping ˜T:Λ→CB(ˆU) is said to be a multivalued SU-type φ-contraction if there exists φ∈φ∗ such that for ˜Tˆℓ∩Λ≠∅
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
φ[ˆHb(˜Tˆℓ∩Λ,˜Tν∩Λ)]≤φ[ξ(Ω(ˆℓ,ν))], | (2.1) |
where
Ω(ˆℓ,ν)=max{db(ˆℓ,ν),db(ˆℓ,˜Tˆℓ),db(ν,˜Tν),db(ˆℓ,˜Tν)+db(ν,˜Tˆℓ)2s} |
for all ˆℓ∈Λ, ν∈˜Tˆℓ∩Λ with db(ˆℓ,ν)∈E, and ˆHb(˜Tˆℓ∩Λ,˜Tν∩Λ)>0.
Clearly in a class b-metric space, if an element ˆℓ0∈Λ such that O(ˆℓ0)⊂Λ satisfies db(ˆℓ0,˜Tˆℓ0)∈E and ¯b(ˆℓi,ρi)⊂Λ for some i≥0, then ˆℓi+1∈Λ and ¯b(ˆℓi+1,ρi+1)⊂¯b(ˆℓi,ρi).
Our first main result is as follows:
Theorem 2.2. Let (ˆU,db) be a complete b-metric space with s≥1, Λ be a closed subset of ˆU and ˜T:Λ→CB(ˆU) be a multivalued SU-type φ -contraction. Assume ˆℓ0∈Λ such that db(ˆℓ0,c∗)∈E for some c∗∈˜Tˆℓ0∩Λ. Then there exist an orbit {ˆℓi} of ˜T in Λ and σ∗∈Λ such that limi→+∞ˆℓi=σ∗. Moreover, σ∗ is a fixed point of ˜T if and only if the function g(ˆℓ):=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-o.l.s.c at σ∗.
Proof. Choose ˆℓ1=c∗∈˜Tˆℓ0∩Λ. In the presence of this manner db(ˆℓ0,ˆℓ1)=0, ˆℓ0 is a fixed point of ˜T. Thus we assume that db(ˆℓ0,ˆℓ1)≠0. On the other hand, we have
12smin{db(ˆℓ0,˜Tˆℓ0∩Λ),db(ˆℓ1,˜Tˆℓ1∩Λ)}<db(ˆℓ0,ˆℓ1). | (2.2) |
Define ρ=σ(db(ˆℓ0,ˆℓ1)). From (1.16), we have σ(r)≥r. Hence db(ˆℓ0,ˆℓ1)≤ρ and so ˆℓ1∈¯b(ˆℓ0,ρ). Since db(ˆℓ0,ˆℓ1)∈E, from (2.1) and (2.2) it follows that
φ[Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)]≤φ[ξ(Ω(ˆℓ0,ˆℓ1))]<φ[Ω(ˆℓ0,ˆℓ1)]. |
By the property of right continuity of φ, there exists a real number h1>1 such that
φ[h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)]≤φ[ξ(Ω(ˆℓ0,ˆℓ1))]. | (2.3) |
From
db(ˆℓ1,˜Tˆℓ1∩Λ)≤Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)<h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ), |
by Lemma 1.3, there exists ˆℓ2∈˜Tˆℓ1∩Λ such that db(ˆℓ1,ˆℓ2)≤h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ). Since φ is nondecreasing, by (2.3), this inequality gives that
φ[(db(ˆℓ1,ˆℓ2)]≤φ[h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)]<φ[Ω(ˆℓ0,ˆℓ1))], |
where
Ω(ˆℓ0,ˆℓ1)=max{db(ˆℓ0,ˆℓ1),db(ˆℓ0,˜Tˆℓ0),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ0,˜Tˆℓ1)+db(ˆℓ1,˜Tˆℓ0)2s}≤max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ0,˜Tˆℓ1)2s}≤max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1)}. |
Now, we claim that
φ[(db(ˆℓ1,ˆℓ2)]≤φ[h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)]<φ[db(ˆℓ0,ˆℓ1))]. | (2.4) |
Let Δ=max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1)}. Assume that Δ=db(ˆℓ1,˜Tˆℓ1). Since ˆℓ2∈˜Tˆℓ1∩Λ, we have
φ[(db(ˆℓ1,ˆℓ2)]≤φ[h1Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)]<φ[db(ˆℓ1,ˆℓ2))], |
which is a contradiction. Hence (2.4) holds true. We assume that db(ˆℓ1,ˆℓ2)≠0, otherwise, ˆℓ1 is a fixed point of ˜T. From (φa), (2.4) implies that
db(ˆℓ1,ˆℓ2)<db(ˆℓ0,ˆℓ1). |
and so db(ˆℓ1,ˆℓ2)∈E. Next, ˆℓ2∈¯b(ˆℓ0,ρ) since
db(ˆℓ0,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+sdb(ˆℓ1,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+s2db(ˆℓ1,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+s2ξ(db(ˆℓ0,ˆℓ1))=s[db(ˆℓ0,ˆℓ1)+sξ(db(ˆℓ0,ˆℓ1))]≤sσdb(ˆℓ0,ˆℓ1)≤db(ˆℓ0,ˆℓ1)+sσ(db(ˆℓ0,ˆℓ1))=σ(db(ˆℓ0,ˆℓ1))=ρ. |
Since
12smin{db(ˆℓ1,˜Tˆℓ1∩Λ),db(ˆℓ2,˜Tˆℓ2∩Λ)}<db(ˆℓ1,ˆℓ2), |
from (2.1), we have
φ[Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)]≤φ[ξ(db(ˆℓ1,ˆℓ2)))]<φ[Ω(ˆℓ1,ˆℓ2))]. |
Since φ is right continuous, there exists a real number h2>1 such that
φ[h2Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ]≤φ[ξ(Ω(ˆℓ1,ˆℓ2))]. | (2.5) |
Next, from
db(ˆℓ2,˜Tˆℓ2∩Λ)≤Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)<h2Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ), |
by Lemma 1.3, there exists ˆℓ3∈˜Tˆℓ2∩Λ such that db(ˆℓ2,ˆℓ3)≤h2Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ). By (2.5), this inequality gives that
φ[(db(ˆℓ2,ˆℓ3))]≤φ[h2Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)]<φ[Ω(ˆℓ1,ˆℓ2))], |
where
Ω(ˆℓ1,ˆℓ2)=max{db(ˆℓ1,ˆℓ2),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ2,˜Tˆℓ2),db(ˆℓ1,˜Tˆℓ2)+db(ˆℓ2,˜Tˆℓ1)2s}≤max{ˆd(ˆℓ1,ˆℓ2),ˆd(ˆℓ2,˜Tˆℓ2),ˆd(ˆℓ1,˜Tˆℓ2)2s}≤max{ˆd(ˆℓ1,ˆℓ2),ˆd(ˆℓ2,˜Tˆℓ2)}. |
This implies that
φ[(ˆd(ˆℓ2,ˆℓ3)]≤φ[h1Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)]<φ[ˆd(ˆℓ1,ˆℓ2))]. | (2.6) |
Let Δ=max{db(ˆℓ1,ˆℓ2),db(ˆℓ2,˜Tˆℓ2)}. Assume that Δ=db(ˆℓ2,˜Tˆℓ2). Since ˆℓ3∈˜Tˆℓ2∩Λ, we have
φ[(db(ˆℓ2,ˆℓ3)]≤φ[h1Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)]<φ[db(ˆℓ2,ˆℓ3))], |
which is a contradiction. Hence (2.6) holds true. We assume that db(ˆℓ2,ˆℓ3)≠0, otherwise, ˆℓ2 is a fixed point of ˜T. From (φa), (2.6) implies that
db(ˆℓ2,ˆℓ3)<db(ˆℓ1,ˆℓ2). |
and so db(ˆℓ2,ˆℓ3)∈E. Also, we have ˆℓ3∈¯b(ˆℓ0,ρ), since
db(ˆℓ0,ˆℓ3)≤sdb(ˆℓ0,ˆℓ1)+s2db(ˆℓ1,ˆℓ2)+s3db(ˆℓ2,ˆℓ3)=s[db(ˆℓ0,ˆℓ1)+sˇdb(ˆℓ1,ˆℓ2)+s2db(ˆℓ2,ˆℓ3)]≤s[db(ˆℓ0,ˆℓ1)+ξ(db(ˆℓ0,ˆℓ1))+ξ2(db(ˆℓ0,ˆℓ1))]≤sσˇdb(ˆℓ0,ˆℓ1)≤db(ˆℓ0,ˆℓ1)+sσ(db(ˆℓ0,ˆℓ1))=σ(db(ˆℓ0,ˆℓ1))=ρ. |
Continuing this manner, we build two sequences {ˆℓi}⊂¯b(ˆℓ0,ρ) and {hi}⊂(0,+∞) such that ˆℓi+1∈˜Tˆℓi∩Λ, ˆℓi≠ˆℓi+1 with db(ˆℓi,ˆℓi+1)∈E and
φ[(db(ˆℓi,ˆℓi+1))]≤φ[hiHb(˜Tˆℓi−1∩Λ,˜Tˆℓi∩Λ)]<φ[db(ˆℓi−1,ˆℓi)], |
for all i∈N. Then
φ[db(ˆℓi,ˆℓi+1)]≤φ[ξi(ˇdb(ˆℓ0,ˆℓ1))], foralli∈N. |
Since φ:(0,+∞)→(0,+∞), it follows from (2.6) that
0≤limi→+∞φ[db(ˆℓi,ˆℓi+1)]≤limi→+∞φ[ξi(db(ˆℓ0,ˆℓ1))]=0, |
which implies that
limi→+∞φ[db(ˆℓi,ˆℓi+1)]=0. |
By (φb) and Lemma 1.2, we have
limi→+∞ˇdb(ˆℓi,ˆℓi+1)=0. | (2.7) |
Next, we prove that {ˆℓi} is a Cauchy sequence in ˆU. Arguing by contradiction, we assume that there are ϵ>0 and sequences {δi}+∞i=1 and {κi}+∞i=1 of natural numbers such that
δi>κi>0,db(ˆℓδi,ˆℓκi)≥ϵanddb(ˆℓδi−1,ˆℓκi)<ϵforalli∈N. |
Therefore,
ϵ≤db(ˆℓδi,ˆℓκi)≤s[db(ˆℓδi,ˆℓδi−1)+db(ˆℓδi−1,ˆℓκi)]≤sˇdb(ˆℓδi,ˆℓδi−1)+sϵ. | (2.8) |
Setting i→+∞ in (2.8),
ϵ<limi→+∞db(ˆℓδi,ˆℓκi)<sϵ. | (2.9) |
From the trianguler inequality, we have
db(ˆℓδi,ˆℓκi)≤db(ˆℓδi,ˆℓδi+1)+db(ˆℓδi+1,ˆℓκi) | (2.10) |
and
db(ˆℓδi+1,ˆℓκi)≤s[ˇdb(ˆℓδi,ˆℓδi+1)+db(ˆℓδi,ˆℓκi)]. | (2.11) |
Letting the upper limit as i→+∞ in (2.10) and applying (2.7) and (2.9), we obtain
ϵ≤limi→+∞supdb(ˆℓδi,ˆℓκi)≤s[limi→+∞supdb(ˆℓδi+1,ˆℓκi)]. |
Again, setting the upper limit as i→+∞ in (2.11), we get
limi→+∞supdb(ˆℓδi+1,ˆℓκi)≤s[limi→+∞supdb(ˆℓδi,ˆℓκi)]≤s.sϵ=s2ϵ. |
Therefore,
ϵs≤limi→+∞supdb(ˆℓδi+1,ˆℓκi)≤s2ϵ, | (2.12) |
equivalently, we have
ϵs≤limi→+∞supdb(ˆℓδi,ˆℓκi+1)≤s2ϵ. | (2.13) |
By the trianguler inequality,
ˇdb(ˆℓδi+1,ˆℓκi)≤s[db(ˆℓδi+1,ˆℓκi+1)+db(ˆℓκi+1,ˆℓκi)]. | (2.14) |
Setting the limit as i→+∞ in (2.14), using (2.7) and (2.12), we have
ϵs2≤limi→+∞supdb(ˆℓδi+1,ˆℓκi+1). | (2.15) |
Owing to above process, we find
limi→+∞supˇdb(ˆℓδi+1,ˆℓκi+1)≤s3ϵ. | (2.16) |
From (2.15) and (2.16), we have
ϵs2≤limi→+∞supdb(ˆℓδi+1,ˆℓκi+1)≤s3ϵ. |
Owing to (2.7) and (2.9), we can choose a positive integer j0≥1 such that
12smin{db(ˆℓδi,˜Tˆℓδi∩Λ),db(ˆℓκi,˜Tˆℓκi∩Λ)}<ϵ2s<ˇdb(ˆℓδi,ˆℓκi) |
for all i≥j0. From (2.1), we have
0<φ[db(ˆℓδi+1,ˆℓκi+1)]≤φ[Hb(˜Tˆℓδi∩Λ,˜Tˆℓκi∩Λ)]≤φ[ξ(Ω(ˆℓδi,ˆℓκi)))], |
where
Ω(ˆℓδi,ˆℓκi)=max{db(ˆℓδi,ˆℓκi),db(ˆℓδi,˜Tˆℓδi),db(ˆℓκi,˜Tˆℓκi),db(ˆℓδi,˜Tˆℓκi)+db(ˆℓκi,˜Tˆℓδi)2s}≤max{db(ˆℓδi,ˆℓκi),db(ˆℓδi,ˆℓδi+1),db(ˆℓκi,ˆℓκi+1),db(ˆℓδi,ˆℓκi+1)+db(ˆℓκi,ˆℓδi+1)2s}. |
Setting the limit as i→+∞ and by (2.7), (2.9), (2.12) and (2.13), we have
ϵ=max{ϵ,12s(ϵs+ϵs)}≤limi→+∞supΩ(ˆℓδi,ˆℓκi)≤max{sϵ,12s(s2ϵ+s2ϵ)}=sϵ. |
By (2.15) and (φb), we have
φ[sϵ]=φ[ϵs2]≤limi→+∞supˇdb(ˆℓδi+1,ˆℓκi+1)≤limi→+∞φ[ξdb(ˆℓδi,ˆℓκi)]=φ[ξ(sϵ)]<φ[sϵ], |
which is a contradiction. Therefore, we deduce that {ˆℓi} is a Cauchy sequence in the closed ball ¯b(ˆℓ0,ρ). Since ¯b(ˆℓ0,ρ) is closed in ˆU, there exists a σ∗∈¯b(ˆℓ0,ρ) such that ˆℓi→σ∗. Note that σ∗∈Λ, since ˆℓi+1∈˜Tˆℓi∩Λ. Next, we claim that
12smin{db(ˆℓi,˜Tˆℓi∩Λ),db(σ∗,˜Tσ∗∩Λ)}<db(ˆℓi,σ∗), | (2.17) |
or
12smin{ˇdb(σ∗,˜Tσ∗∩Λ),db(ˆℓi+1,˜Tˆℓi+1∩Λ)}<db(ˆℓi+1,σ∗) |
for all i∈N. Assume, on contrary, there exists i′∈N such that
12smin{db(ˆℓi′,˜Tˆℓi′∩Λ),ˇdb(σ∗,˜Tσ∗∩Λ)}≥db(ˆℓi′,σ∗) | (2.18) |
and
12smin{db(σ∗,˜Tσ∗∩Λ),db(ˆℓi′+1,˜Tˆℓi′+1∩Λ)}≥db(ˆℓi′+1,σ∗). | (2.19) |
By (2.18), we have
2sˇdb(ˆℓi′,σ∗)≤min{db(ˆℓi′,˜Tˆℓi′∩Λ),db(σ∗,˜Tσ∗∩Λ)}≤min{s[db(ˆℓi′,σ∗)+db(σ∗,˜Tˆℓi′∩Λ)],ˇdb(σ∗,˜Tσ∗∩Λ)}≤s[db(ˆℓi′,σ∗)+db(σ∗,˜Tˆℓi′∩Λ)]<s[db(ˆℓi′,σ∗)+ˇdb(σ∗,˜Tˆℓi′)]≤s[db(ˆℓi′,σ∗)+db(σ∗,ˆℓi′+1)], |
which implies that
db(ˆℓi′,σ∗)≤db(σ∗,ˆℓi′+1). |
This together with (2.19) implies
db(ˆℓi′,σ∗)≤db(σ∗,ˆℓi′+1)≤12smin{db(σ∗,˜Tσ∗∩Λ),db(ˆℓi′+1,˜Tˆℓi′+1∩Λ)}. | (2.20) |
So
12smin{db(ˆℓi′,˜Tˆℓi′∩Λ),ˇdb(ˆℓi′+1,˜Tˆℓi′+1∩Λ)}<db(ˆℓi′,ˆℓi′+1). |
From the contractive condition (2.1), we have
0<φ[db(ˆℓi′+1,ˆℓi′+2)]≤φ[Hb(˜Tˆℓi′∩Λ,˜Tˆℓi′+1∩Λ)]≤φ[ξ(c(ˆℓi′,ˆℓi′+1)))], |
where
Ω(ˆℓi′,ˆℓi′+1)=max{db(ˆℓi′,ˆℓi′+1),db(ˆℓi′,˜Tˆℓi′),ˇdb(ˆℓi′+1,˜Tˆℓi′+1),db(ˆℓi′,˜Tˆℓi′+1)+db(ˆℓi′+1,˜Tˆℓi′)2s}≤max{db(ˆℓi′,ˆℓi′+1),ˇdb(ˆℓi′+1,ˆℓi′+2),db(ˆℓi′,ˆℓi′+2)2s}≤max{db(ˆℓi′,ˆℓi′+1),db(ˆℓi′+1,ˆℓi′+2)}, |
which yields
φ[ˇdb(ˆℓi′+1,ˆℓi′+2)]≤φ[Hb(˜Tˆℓi′∩Λ,˜Tˆℓi′+1∩Λ)]<φ[db(ˆℓi′,ˆℓi′+1))]. |
Let Δ=max{db(ˆℓi′,ˆℓi′+1),db(ˆℓi′+1,ˆℓi′+2)}. Assume that Δ=db(ˆℓi′+1,ˆℓi′+2). Since ˆℓi′+2∈˜Tˆℓi′+1∩Λ, we have
φ[db(ˆℓi′+1,ˆℓi′+2)]≤φ[Hb(˜Tˆℓi′∩Λ,˜Tˆℓi′+1∩Λ)]<φ[db(ˆℓi′+1,ˆℓi′+2))], |
which is a contradiction. Owing to (φa), we have
ˇdb(ˆℓi′+1,ˆℓi′+2)<db(ˆℓi′,ˆℓi′+1). | (2.21) |
From (2.19), (2.20) and (2.21), we obtain
db(ˆℓi′+1,ˆℓi′+2)<db(ˆℓi′,ˆℓi′+1)≤s[ˇdb(ˆℓi′,σ∗)+db(σ∗,ˆℓi′+1)]≤[12min{db(σ∗,˜Tσ∗∩Λ),db(ˆℓi′+1,˜Tˆℓi′+1∩Λ)}+12min{ˇdb(σ∗,˜Tσ∗∩Λ),db(ˆℓi′+1,˜Tˆℓi′+1∩Λ)}]≤min{db(σ∗,˜Tσ∗∩Λ),db(ˆℓi′+1,ˆℓi′+2)}=db(ˆℓi′+1,ˆℓi′+2), |
which is a contradiction. Hence (2.17) holds true, that is,
12smin{ˇdb(ˆℓi,˜Tˆℓi∩Λ),db(σ∗,˜Tσ∗∩Λ)}<db(ˆℓi,σ∗)foralli≥2. | (2.22) |
Owing to (2.22), we have
12smin{db(ˆℓi,˜Tˆℓi∩Λ),db(ˆℓi+1,˜Tˆℓi+1∩Λ)}<db(ˆℓi,ˆℓi+1). |
Moreover, we know that db(ˆℓi,ˆℓi+1)∈E for all i. Thus, from (2.1), we have
φ[db(ˆℓi+1,˜Tˆℓi+1∩Λ)]≤φ[Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ)]≤φ[ξ(Ω(ˆℓi,ˆℓi+1)))]<φ[Ω(ˆℓi,ˆℓi+1)))], |
where
Ω(ˆℓi,ˆℓi+1)=max{db(ˆℓi,ˆℓi+1),db(ˆℓi,˜Tˆℓi),db(ˆℓi+1,˜Tˆℓi+1),db(ˆℓi,˜Tˆℓi+1)+db(ˆℓi+1,˜Tˆℓi)2s}≤max{db(ˆℓi,ˆℓi+1),db(ˆℓi+1,ˆℓi+2),db(ˆℓi,ˆℓi+2)2s}≤max{db(ˆℓi,ˆℓi+1),db(ˆℓi+1,ˆℓi+2)}, |
which implies
φ[db(ˆℓi+1,ˆℓi+2)]≤φ[Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ)]<φ[db(ˆℓi,ˆℓi+1))]. |
Let Δ=max{db(ˆℓi,ˆℓi+1),db(ˆℓi+1,ˆℓi+2)}. Assume that Δ=db(ˆℓi+1,ˆℓi+2). Since ˆℓi+2∈˜Tˆℓi+1∩Λ, we have
φ[db(ˆℓi+1,ˆℓi+2)]≤φ[Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ)]<φ[db(ˆℓi+1,ˆℓi+2))], |
which is a contradiction. Also, by (φa), we deduce that
db(ˆℓi+1,˜Tˆℓi+1∩Λ)<db(ˆℓi,ˆℓi+1). | (2.23) |
Taking the limit i→+∞ in (2.23), we get
limi→+∞db(ˆℓi+1,˜Tˆℓi+1∩Λ)=0. |
Since g(ˆℓ)=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-o.l.s.c at σ∗,
db(σ∗,˜Tσ∗∩Λ)=g(σ∗)≤lim infig(ˆℓi+1)=lim infidb(ˆℓi+1,˜Tˆℓi+1∩Λ)=0. |
Since ˜Tσ∗ is closed, we have σ∗∈˜Tσ∗. Conversely, if σ∗ is a fixed point of ˜T then g(σ∗)=0≤lim infig(ˆℓi), since σ∗∈Λ.
Corollary 2.3. Let (ˆU,db) be a b-metric space with s≥1, Λ be a closed subset of ˆU and ξ be a b-B-GGF on an interval E. A mapping ˜T:Λ→CB(ˆU) is said to be a multivalued SU-type φ-contraction if there exists φ∈φ∗ such that for ˜Tˆℓ∩Λ≠∅
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
φ[Hb(˜Tˆℓ∩Λ,˜Tν∩Λ)]≤φ[ξ((ˆℓ,ν)))], |
for all ˆℓ∈Λ, ν∈˜Tˆℓ∩Λ with db(ˆℓ,ν)∈E, where Hb(˜Tˆℓ∩Λ,˜Tν∩Λ)>0. Assume ˆℓ0∈Λ such that db(ˆℓ0,c∗)∈E for some c∗∈˜Tˆℓ0∩Λ. Then there exist an orbit {ˆℓi} of ˜T in Λ and σ∗∈Λ such that limi→+∞ˆℓi=σ∗. Moreover, σ∗ is a fixed point of ˜T if and only if the function g(ˆℓ):=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-o.l.s.c at σ∗.
Corollary 2.4. Let (ˆU,db) be a b-metric space with s≥1, Λ be a closed subset of ˆU and ξ be a b-B-GGF on an interval E. A mapping ˜T:Λ→CB(ˆU) is said to be a multivalued SU-type φ-contraction if there exists φ∈φ∗ such that for ˜Tˆℓ∩Λ≠∅
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
φ[Hb(˜Tˆℓ∩Λ,˜Tν∩Λ)]≤φ[ξ(db(ˆℓ,ν)))], |
for all ˆℓ∈ˆU, ν∈˜Tˆℓ with db(ˆℓ,ν)∈E. Suppose that ˆℓ0∈ˆU such that db(ˆℓ0,c∗)∈E for some c∗∈˜Tˆℓ0. Then there exists an orbit {ˆℓi} of ˜T in ˆU which converges to the fixed point σ∗∈F={ˆℓ∈ˆU:db(ˆℓ,σ∗)∈E} of ˜T.
Example 2.5. Let ˆU=[0,1] be endowed with the metric db with coefficient s≥α2+7α2−1>1 [where α≥3 is any positive integers] as defined by db(ˆℓ,ν)=|ˆℓ−ν|2 for all ˆℓ,ν∈ˆU but not a metric bd. For ˆℓ1=0, ˆℓ2=12 and ˆℓ3=1, we obtain
bd(ˆℓ1,ˆℓ3)=1>14+14=bd(ˆℓ1,ˆℓ2)+bd(ˆℓ2,ˆℓ3) |
and let E=[0,+∞). Consider the mapping ˜T:ˆU→CB(ˆU) defined by ˜T(ˆℓ)=[0,ˆℓ2]. Clearly,
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
if and only if ˆℓ,ν∈[0,1]. Let ˆℓ0=1. Then we have c∗=12∈˜Tˆℓ0 such that db(ˆℓ0,c∗)∈E and
φ[Hb(˜Tˆℓ,˜Tν)]=φ[|ˆℓ2−ν2|2]≤φ[|ˆℓ+ν|2db(ˆℓ,ν)]. |
Set φ(r)=rer for all r>0 and suppose that ξ(r)=r2 is a b -B-GGF of order 2 on E=[0,1α−1] with coefficient α2+7α2−1. For any ˆℓ∈[0,1] and ν∈˜Tˆℓ, we get
φ[Hb(˜Tˆℓ,˜Tν)]≤[|ˆℓ+ν|2db(ˆℓ,ν)]e[|ˆℓ+ν|2db(ˆℓ,ν)]=φ[ξ(db(ˆℓ,ν))]. |
Thus, all the conditions of Corollary 2.3 are fulfilled and 0 is a fixed point of ˜T.
In this section, motivated by the notion of multivalued Suzuki type ∇ -contraction, we define the notion of multivalued Suzuki type (∇α−ξ)-contraction as follows:
Definition 3.1. Let (ˆU,db) be a b-metric space with s≥1, Λ be a closed subset of ˆU and ξ be a b-B-GGF on an interval E. A mapping ˜T:Λ→CB(ˆU) is said to be a multivalued Suzuki type (∇α−ξ)-contraction if there exists Γ∈∇ such that for ˜Tˆℓ∩Λ≠∅
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
Γ[α(ˆℓ,ν)Hb(˜Tˆℓ∩Λ,˜Tν∩Λ),ξ(Ω(ˆℓ,ν))]≥0, | (3.1) |
where
Ω(ˆℓ,ν)=max{db(ˆℓ,ν),db(ˆℓ,˜Tˆℓ),db(ν,˜Tν),db(ˆℓ,˜Tν)+db(ν,˜Tˆℓ)2s} |
for all ˆℓ∈Λ, ν∈˜Tˆℓ∩Λ with db(ˆℓ,ν)∈E.
The second one of our results is as follows.
Theorem 3.2. Let (ˆU,db) be a complete b-metric space with s≥1, Λ be a closed subset of ˆU and ˜T:Λ→CB(ˆU) be a multivalued SU-type (α-∇)-contraction. Suppose that the following conditions are satisfied:
(i) ˜T is α-admissible;
(ii) there exists ˆℓ0∈Λ with db(ˆℓ0,ˆℓ1)∈E for some ˆℓ1∈˜Tˆℓ0∩Λ such that α(ˆℓ0,ˆℓ1)≥1.
Then there exist an orbit {ˆℓi} of ˜T in Λ and σ∗∈Λ such that limi→+∞ˆℓi=σ∗. Moreover, σ∗ is a fixed point of ˜T if and only if the function g(ˆℓ):=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-o.l.s.c at σ∗.
Proof. Owing to the hypothesis, there exists ˆℓ0∈Λ with db(ˆℓ0,ˆℓ1)∈E for some ˆℓ1∈˜Tˆℓ0∩Λ such that α(ˆℓ0,ˆℓ1)≥1. On the other hand, we have
12smin{db(ˆℓ0,˜Tˆℓ0∩Λ),db(ˆℓ1,˜Tˆℓ1∩Λ)}<db(ˆℓ0,ˆℓ1). | (3.2) |
If db(ˆℓ0,ˆℓ1)=0, then ˆℓ0 is a fixed point of ˜T. Thus, we assume that db(ˆℓ0,ˆℓ1)≠0. Define ρ=σ(db(ˆℓ0,ˆℓ1)). From (1.16), we have σ(r)≥r. Hence db(ˆℓ0,ˆℓ1)≤ρ and so ˆℓ1∈¯b(ˆℓ0,ρ). Since α(ˆℓ0,ˆℓ1)≥1 and db(ˆℓ0,ˆℓ1)∈E, from (3.1) and (3.2), it follows that
0≤Γ[α(ˆℓ0,ˆℓ1)Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ),ξ(db(ˆℓ0,ˆℓ1))]<ξ(Ω(ˆℓ0,ˆℓ1))−α(ˆℓ0,ˆℓ1)Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ), |
which implies
α(ˆℓ0,ˆℓ1)Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)<ξ(Ω(ˆℓ0,ˆℓ1)). |
We can choose an ϵ1>0 such that
α(ˆℓ0,ˆℓ1)Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)+ϵ1≤ξ(Ω(ˆℓ0,ˆℓ1)). |
Thus
db(ˆℓ1,˜Tˆℓ1∩Λ)+ϵ1≤Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)+ϵ1≤α(ˆℓ0,ˆℓ1)Hb(˜Tˆℓ0∩Λ,˜Tˆℓ1∩Λ)+ϵ1≤ξ(Ω(ˆℓ0,ˆℓ1)). | (3.3) |
It follows from Lemma 1.2 that there exists ˆℓ2∈˜Tˆℓ1∩Λ such that
db(ˆℓ1,ˆℓ2)≤db(ˆℓ1,˜Tˆℓ1∩Λ)+ϵ1. | (3.4) |
From (3.3) and (3.4), we have
db(ˆℓ1,ˆℓ2)≤ξ(Ω(ˆℓ0,ˆℓ1)), |
where
Ω(ˆℓ0,ˆℓ1)=max{db(ˆℓ0,ˆℓ1),db(ˆℓ0,˜Tˆℓ0),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ0,˜Tˆℓ1)+db(ˆℓ1,˜Tˆℓ0)2s}≤max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ0,˜Tˆℓ1)2s}≤max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1)}. |
We claim that
db(ˆℓ1,ˆℓ2)≤ξ(db(ˆℓ0,ˆℓ1)). | (3.5) |
Let Δ=max{db(ˆℓ0,ˆℓ1),db(ˆℓ1,˜Tˆℓ1)}. Assume that Δ=db(ˆℓ1,˜Tˆℓ1). Since ˆℓ2∈˜Tˆℓ1∩Λ, we have
(db(ˆℓ1,ˆℓ2)≤ξ(db(ˆℓ1,ˆℓ2)), |
which is a contradiction. Hence (3.5) holds true. We assume that db(ˆℓ1,ˆℓ2)≠0, otherwise, ˆℓ1 is a fixed point of ˜T. Since db(ˆℓ1,ˆℓ2)≤ξ(db(ˆℓ0,ˆℓ1))<db(ˆℓ0,ˆℓ1), we deduce that db(ˆℓ1,ˆℓ2)∈E. Next, ˆℓ2∈¯b(ˆℓ0,ρ) since
db(ˆℓ0,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+sdb(ˆℓ1,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+s2db(ˆℓ1,ˆℓ2)≤sdb(ˆℓ0,ˆℓ1)+s2ξ(db(ˆℓ0,ˆℓ1))=s[db(ˆℓ0,ˆℓ1)+sξ(db(ˆℓ0,ˆℓ1))]≤sσdb(ˆℓ0,ˆℓ1)≤db(ˆℓ0,ˆℓ1)+sσ(db(ˆℓ0,ˆℓ1))=σ(db(ˆℓ0,ˆℓ1))=ρ.. |
Since ˜T is α-admissible, α(ˆℓ1,ˆℓ2)≥1. Also, since
12smin{db(ˆℓ1,˜Tˆℓ1∩Λ),db(ˆℓ2,˜Tˆℓ2∩Λ)}<db(ˆℓ1,ˆℓ2), |
from the contractive condition (3.1), we get
0≤Γ[α(ˆℓ1,ˆℓ2)Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ),ξ(Ω(ˆℓ1,ˆℓ2))]<ξ(Ω(ˆℓ1,ˆℓ2))−α(ˆℓ1,ˆℓ2)Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ). |
This implies that
α(ˆℓ1,ˆℓ2)Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)<ξ(Ω(ˆℓ1,ˆℓ2)). |
Now choose an ϵ2>0 such that
α(ˆℓ1,ˆℓ2)Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)+ϵ2≤ξ(Ω(ˆℓ1,ˆℓ2)). |
Thus,
db(ˆℓ2,˜Tˆℓ2∩Λ)+ϵ2≤Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)+ϵ2≤α(ˆℓ1,ˆℓ2)Hb(˜Tˆℓ1∩Λ,˜Tˆℓ2∩Λ)+ϵ2≤ξ(Ω(ˆℓ1,ˆℓ2)). | (3.6) |
It follows from Lemma 1.2 that there exists ˆℓ3∈˜Tˆℓ2∩Λ such that
db(ˆℓ2,ˆℓ3)≤db(ˆℓ2,˜Tˆℓ2∩Λ)+ϵ2. | (3.7) |
From (3.6) and (3.7), we obtain
db(ˆℓ2,ˆℓ3)≤ξ(Ω(ˆℓ1,ˆℓ2)), |
where
Ω(ˆℓ1,ˆℓ2)=max{db(ˆℓ1,ˆℓ2),db(ˆℓ1,˜Tˆℓ1),db(ˆℓ2,˜Tˆℓ2),db(ˆℓ1,˜Tˆℓ2)+db(ˆℓ2,˜Tˆℓ1)2s}≤max{db(ˆℓ1,ˆℓ2),db(ˆℓ2,˜Tˆℓ2),db(ˆℓ1,˜Tˆℓ2)2s}≤max{db(ˆℓ1,ˆℓ2),db(ˆℓ2,˜Tˆℓ2)}. |
This implies that
db(ˆℓ2,ˆℓ3)≤ξdb(ˆℓ1,ˆℓ2)). | (3.8) |
Let Δ=max{db(ˆℓ1,ˆℓ2),db(ˆℓ2,˜Tˆℓ2)}. Assume that Δ=db(ˆℓ2,˜Tˆℓ2). Since ˆℓ3∈˜Tˆℓ2∩Λ, we have
db(ˆℓ2,ˆℓ3)≤ξˆd(ˆℓ2,ˆℓ3)), |
which is a contradiction. Hence (3.8) holds true. We assume that db(ˆℓ2,ˆℓ3)≠0, otherwise, ˆℓ2 is a fixed point of ˜T. From (3.8), we have db(ˆℓ2,ˆℓ3)<db(ˆℓ1,ˆℓ2) and so db(ˆℓ2,ˆℓ3)∈E. Also, we have ˆℓ3∈¯b(ˆℓ0,ρ), since
db(ˆℓ0,ˆℓ3)≤sdb(ˆℓ0,ˆℓ1)+s2db(ˆℓ1,ˆℓ2)+s3db(ˆℓ2,ˆℓ3)=s[db(ˆℓ0,ˆℓ1)+sdb(ˆℓ1,ˆℓ2)+s2db(ˆℓ2,ˆℓ3)]≤s[db(ˆℓ0,ˆℓ1)+ξ(db(ˆℓ0,ˆℓ1))+ξ2(db(ˆℓ0,ˆℓ1))]≤sσdb(ˆℓ0,ˆℓ1)≤db(ˆℓ0,ˆℓ1)+sσ(db(ˆℓ0,ˆℓ1))=σ(db(ˆℓ0,ˆℓ1))=ρ. |
Continuing this manner, we obtain a sequence {ˆℓi}⊂¯b(ˆℓ0,ρ) such that ˆℓi+1∈˜Tˆℓi∩Λ, ˆℓi≠ˆℓi+1 with α(ˆℓi,ˆℓi+1)≥1, db(ˆℓi,ˆℓi+1)∈E and by the above hypothesis, we have
db(ˆℓi,ˆℓi+1)≤ξi(db(ˆℓ0,ˆℓ1)), foralli∈N. | (3.9) |
For any q∈N, by using the triangular inequality and (3.9), we get
db(ˆℓi,ˆℓi+q)≤sidb(ˆℓi,ˆℓi+1)+si+1db(ˆℓi+1,ˆℓi+2)+⋯+si+q−1db(ˆℓi+q−1,ˆℓi+q)≤siξi(db(ˆℓ0,ˆℓ1))+si+1ξi+1(db(ˆℓ0,ˆℓ1))+⋯+si+q−1ξi+q−1(db(ˆℓ0,ˆℓ1))≤∞∑j=isjξj(db(ˆℓ0,ˆℓ1))<∞. | (3.10) |
Assume that
Hi=∞∑j=isjξj(db(ˆℓ0,ˆℓ1))andlimi→+∞Hi=H. | (3.11) |
By (3.10) and (3.11), we get
db(ˆℓi,ˆℓi+q)≤(Hi+q−1−Hi). | (3.12) |
Due to (3.11), (3.12) implies that db(ˆℓi,ˆℓi+q)→0 as i→+∞. Hence {ˆℓi} is a Cauchy sequence in the closed ball ¯b(ˆℓ0,ρ). Since ¯b(ˆℓ0,ρ) is closed in ˆU, there exists an σ∗∈¯b(ˆℓ0,ρ) such that ˆℓi→σ∗. Note that σ∗∈Λ, since ˆℓi+1∈˜Tˆℓi∩Λ. By the same argument as in Theorem 2.2, we have
12smin{db(ˆℓi,˜Tˆℓi∩Λ),db(ˆℓi+1,˜Tˆℓi+1∩Λ)}<db(ˆℓi,ˆℓi+1). |
Also, we know that α(ˆℓi,ˆℓi+1)≥1 and db(ˆℓi,ˆℓi+1)∈E for all n. Thus, from (3.1), we have
0≤Γ[α(ˆℓi,ˆℓi+1)Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ),ξ(Ω(ˆℓi,ˆℓi+1))]<ξ(Ω(ˆℓi,ˆℓi+1))−α(ˆℓi,ˆℓi+1)Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ), |
which gives that
α(ˆℓi,ˆℓi+1)Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ)<ξ(Ω(ˆℓi,ˆℓi+1)). |
Since ˆℓi+1∈˜Tˆℓi∩Λ, from (3.9), we get
db(ˆℓi+1,˜Tˆℓi+1∩Λ)≤α(ˆℓi,ˆℓi+1)Hb(˜Tˆℓi∩Λ,˜Tˆℓi+1∩Λ)<ξ(db(ˆℓi,ˆℓi+1))≤ξi+1(db(ˆℓ0,ˆℓ1)). | (3.13) |
Taking the limit i→+∞ in (3.13), we obtain
limi→+∞db(ˆℓi+1,˜Tˆℓi+1∩Λ)=0. |
Since g(ˆℓ)=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-orbitally lower semi-continuous at σ∗,
db(σ∗,˜Tσ∗∩Λ)=g(σ∗)≤lim infig(ˆℓi+1)=lim infiˇdb(ˆℓi+1,˜Tˆℓi+1∩Λ)=0. |
Since ˜Tσ∗ is closed, we have σ∗∈˜Tσ∗. Conversely, if σ∗ is a fixed point of ˜T then g(σ∗)=0≤lim infig(ˆℓi), since σ∗∈Λ.
Setting Γ(r,s)=s−∫r0ς(t)dtforallr,s≥0 in Theorem 3.2, we get the following result.
Corollary 3.3. Let (ˆU,db) be a complete b-metric space with s≥1, Λ be a closed subset of ˆU, ξ be a b-B-GGF on an interval E and let ˜T:Λ→CB(ˆU) be a given multivalued mapping. Suppose that for ˜Tˆℓ∩Λ≠∅ such that
12smin{db(ˆℓ,˜Tˆℓ∩Λ),db(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
∫α(ˆℓ,ν)Hb(˜Tˆℓ∩Λ,˜Tν∩Λ)0ς(t)dt≤ξ(ˆd(ˆℓ,ν)) |
for all ˆℓ∈Λ, ν∈˜Tˆℓ∩Λ with ˆd(ˆℓ,ν)∈E, where ς:R+→R+ is a function such that ∫ϵ0ς(t)dt exists and ∫ϵ0ς(t)dt>ϵ for all ϵ>0. Suppose that the following conditions are satisfied:
(i) ˜T is α-admissible;
(ii) there exists ˆℓ0∈Λ with db(ˆℓ0,ˆℓ1)∈E for some ˆℓ1∈˜Tˆℓ0∩Λ such that α(ˆℓ0,ˆℓ1)≥1.
Then there exist an orbit {ˆℓi} of ˜T in Λ and σ∗∈Λ such that limi→+∞ˆℓi=σ∗. Moreover, σ∗ is a fixed point of ˜T if and only if the function g(ˆℓ):=db(ˆℓ,˜Tˆℓ∩Λ) is ˜T-o.l.s.c at σ∗.
Corollary 3.4. Let (ˆU,db) be a complete b-metric space with s≥1, ξ be b -B-GGF on an interval E and let ˜T:ˆU→CB(ˆU) be a given multivalued mapping. Suupose that there exist ψ∈Φ and Γ∈∇ such that
12smin{db(ˆℓ,˜Tˆℓ∩Λ),ˇdb(ν,˜Tν∩Λ)}<db(ˆℓ,ν) |
implies that
Γ[α(ˆℓ,ν)Hb(˜Tˆℓ,˜Tν),ξ(db(ˆℓ,ν))]≥0 |
for all ˆℓ∈ˆU, ν∈˜Tˆℓ with db(ˆℓ,ν)∈E. Suppose that the following conditions are satisfied:
(i) ˜T is α-admissible;
(ii) there exists ˆℓ0∈ˆU with db(ˆℓ0,ˆℓ1)∈E for some ˆℓ1∈˜Tˆℓ0 such thatα(ˆℓ0,ˆℓ1)≥1.
Then there exists an orbit {ˆℓi} of ˜T in ˆU which converges to the fixed point σ∗∈F={ˆℓ∈ˆU:db(ˆℓ,σ∗)∈E} of ˜T.
In the recent past, Banach's fixed point theorem has a broad family of important applications to an iteration methods for the system of linear algebraic equation and the most publicized application of Banach's fixed point theorem emarge in the module of function spaces. This yields the existence of solution for the system of differential and integral equations (see [3]). In this section, we investigate Corollary 2.4 to stabilize the existence of solution for the system of integral inclusions.
Consider the following system of integral inclusion:
ς(r)∈κ+U∫rr0D(t,ς(t))dt, | (4.1) |
where κ∈(−∞,+∞), U is a bounded compact subset of (−∞,+∞) and the operator D(t,ς(t)) is lower semi-continuous. Let ˆU=C(I) be the space of all continuous real valued functions (C(I) is complete with respect to the metric db) endowed with the b-metric defined by
db(ˆℓ1,ˆℓ2)=supr∈I|ˆℓ1(r)−ˆℓ2(r)|. |
Assume that there exists D:(−∞,+∞)×(−∞,+∞)→(−∞,+∞) which is continuous on
Γ={(r,ς):|r−r0|≤[αh−21αh−11]and|ς−κ|≤12(α2α1)} |
where α1=maxu∈U|U|, 0<α2<α1 and h≥2 such that
|D(r,ς1(r))−D(r,ς2(r))|≤α1α2|ς1(r)−ς2(r)|h, |
where D is bounded as
|D(t,ς)|<12[α2α1]h. |
Moreover, let ˇC={ς∈C(I):ˆV(ς,κ)≤12α2} be a closed subspace of C(I) and the operator g be defined by
g(ς(r))∈κ+U∫rr0V(t,ς(t))dt. |
Set VˆU(r)=∫rr0V(t,ς(t))dt. Note that
Hb[g(ς1(r)),g(ς2(r))]=Hb[κ+UVˆU(r),κ+UVy(r)]≤Hb[UVˆU(r),UVy(r)]=max{max¯a∈UVˆU(r)ˇdb(¯a,UVy(r)),max¯b∈UVy(r)db(¯b,UVˆU(r))}. | (4.2) |
Then
max¯a∈UVˆU(r)db(¯a,UVy(r))=max¯a∈UVˆU(r)min¯b∈UVy(r)db(¯a,¯b)=max¯u∈Umin¯v∈Uˇdb(¯uV(r,ς1(r)),¯vV(r,ς2(r)))=max¯u∈Umin¯v∈Usupr∈I|¯uV(r,ς1(r))−¯vV(r,ς2(r))|≤max¯u∈Umin¯v∈Usupr∈I[|¯uV(r,ς2(r))−¯vV(r,ς2(r))|+|¯uV(r,ς2(r))−¯uV(r,ς1(r))|]≤max¯u∈Umin¯v∈U[|¯u|supr∈I|V(r,ς2(r))−V(r,ς1(r))|+|¯u−¯v|supr∈I|V(r,ς2(r))|]=max¯u∈U|¯u|supr∈I|V(r,ς2(r))−V(r,ς1(r))|=α2supr∈I|V(r,ς2(r))−V(r,ς1(r))|. |
This implies that
max¯a∈UVˆU(r)d(¯a,UVy(r))≤α2supr∈I|V(r,ς2(r))−V(r,ς1(r))|. | (4.3) |
The third one of our results is as follows:
Theorem 4.1. Let ˆU=C(I) be the space of all continuous real valued functions and g:(ˇC,d)→(V(ˇC),Hb) be a lower semi-continuous mapping. Suppose that the following assumptions hold:
(i) g is defined for all ς∈ˇC;
(ii) g(ς(r)) is a compact subset of ˇC for all ς∈ˇC;
Then the integral equation (4.3) has a solution on
I=[r0−αh−21αh−11,r0+αh−21αh−11]. |
Proof. Let ϰ∈I. Then |ϰ−r0|≤[αh−21αh−11]. Hence we have |ς(ϰ)−κ|≤12(α2α1). If (ϰ,ς(ϰ))∈(−∞,+∞), then the integral equation in (4.1) exists. Since κ∈(−∞,+∞) is continuous, ϰ is defined for all ϰ∈ˇC. Next, let ϑ(r)∈g(ς(r)). Then ϑ(r)=κ+¯uVˆU(r) for ¯u∈U and so
|ϑ(r)−κ|=|¯uVˆU(r)|=|¯u||VˆU(r)|≤α1∫rr0|V(t,ς(t))dt|≤α1∫rr0|V(t,ς(t))|dt<α112(α2α1)h≤12(α2α1). |
Thus |ϑ(r)−κ|≤12(α2α1) for all ϑ(r)∈g(ς(r)). So g(ς(r)) is a subset of ˇC. Now, let {ςi}⊂g(ς(r)). Then ς=κ+¯uiDˆU(r) for ¯ui∈U. Since U is compact, there exists a subsequence ^ui∗∈^ui such that {^ui∗} is convergent to ¯u∈U. Let ˆu=κ+ˆuVˆU(r). Then
d(^ui∗,ˆu)=supr∈I(|^ui∗−ˆu||VˆU(r)|)≤|^ui∗−ˆu|supr∈I|VˆU(r)|→0,asi∗→+∞. |
Hence g(ς(r)) is a compact subset of ˇC for all ς∈ˇC. Next,
|V(r,ς1(r))−V(r,ς2(r))|≤∫rr0|V(t,ς1(t))−V(t,ς2(t))|dt≤α2α1∫rr0|ς1(t)−ς2(t)|hdt≤α2α1supr∈I|ς1(t)−ς2(t)|h∫rr0dt=α2α1|r−r0|[db(ς1,ς2)]h≤1α1(α1α2)h−2[db(ς1,ς2)]h. |
Therefore, we get
max¯a∈UVˆU(r)db(¯a,UVy(r))≤(α1α2)h−2[db(ς1,ς2)]h. |
Similarly,
max¯b∈UVy(r)db(¯b,UVˆU(r))≤(α1α2)h−2[db(ˆℓ1,ˆℓ2)]h. |
Hence (4.2) implies that
Hb[db(g(ϖ1),g(ϖ2))]≤(α1α2)h−2[ˇdb(ς1,ς2)]h. |
Taking φ(ς)=ς, ς>0 and ξ(ς)=(α1α2)h−2ςh, ς∈E with db(ς1,ς2)<α2α1, we get
φ[Hbdb(g(ϖ1),g(ϖ2))]≤φ[ξ(db(ϖ1,ϖ2))]forall;ϖ1,ϖ2∈ˇCwithdb(ς1,ς2)∈E. |
Hence the requied conditions (i)-(ii) are equivalent to (a)-(b) of Corollary 2.3. So there exists a fixed point c∗(∈Λ) in ˇC, which is a bounded solution of (4.1).
The paper deals with the pre-existing results of fixed point for multi-valued maps satisfying φ-contraction via b-B-GGF in the context of b-metric space. Within this frame work, we introduced two related fixed point results in b-metric space. Afterwards, the results have been explained by rendering concrete examples and some foremost corollaries have been deduced from the main results. At the end, we have proved existence theorem for the system of multi-valued integral inclusion.
We would like to express our sincere gratitude to the anonymous referee for his/her helpful comments that will help to improve the quality of the manuscript.
The authors declare that they have no competing interests.
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