Introducing soft directed hypergraphs: a fusion of soft set theory and directed hypergraphs

Bobin George1, Jinta Jose2, Rajesh K. Thumbakara3
1Department of Mathematics, Pavanatma College Murickassery, Kerala, India
2Department of Science and Humanities, Viswajyothi College of Engineering and Technology Vazhakulam, Kerala, India
3Department of Mathematics, Mar Athanasius College (Autonomous) Kothamangalam, Kerala, India

Abstract

Directed hypergraphs represent a natural extension of directed graphs, while soft set theory provides a method for addressing vagueness and uncertainty. This paper introduces the notion of soft directed hypergraphs by integrating soft set principles into directed hypergraphs. Through parameterization, soft directed hypergraphs yield a sequence of relation descriptions derived from a directed hypergraph. Additionally, we present several operations for soft directed hypergraphs, including extended union, restricted union, extended intersection, and restricted intersection, and explore their characteristics.

Keywords: Directed Hypergraph, Soft Directed Hypergraph

1. Introduction

Directed hypergraphs [7,8,10] serve as a powerful modelling tool in both Operations Research and Computer Science, offering a broader representation than traditional directed graphs. They allow for the representation of relationships among multiple entities, making them particularly useful in scenarios where complex interactions need to be captured.

The concept of soft sets, pioneered by Molodtsov [27] in 1999, revolutionized mathematical approaches to dealing with uncertainties that evade conventional methods. Soft sets provide a flexible framework for handling imprecise or uncertain information, enabling more robust decision-making processes. Subsequent research by Maji, Roy, and Biswas [25,26] has delved deeper into the theory of soft sets, exploring their applications in various decision-making contexts.

Thumbakara and George [31] introduced soft graphs and some of their properties [33,34], which have since been refined and extended by researchers like Akram and Nawas [2,3]. Their work has led to the development of fuzzy soft graphs and fuzzy soft trees, further expanding the applicability of soft graph theory [4,5,6]. Contributions from Thenge, Jain, and Reddy [30,28,29] have also significantly advanced the field of soft graphs.

George, Thumbakara, and Jose have made substantial contributions to the domain by introducing concepts such as soft hypergraphs [11] and soft directed graphs [23,22]. These extensions have broadened the scope of soft graph theory, enabling the modelling of more complex systems and phenomena. Moreover, they have investigated various product operations on soft graphs, including modular products and homomorphic products, which have implications for graph analysis and manipulation [12,14,15,19,21,20,24].

Baghernejad and Borzooei [9] have demonstrated the practical utility of soft graphs and soft multigraphs in managing urban traffic flows, showcasing the real-world applicability of these theoretical constructs. Additionally, innovations like soft semigraphs [13,18,17] and soft disemigraphs [16] have further enriched the field, providing new avenues for exploration and application.

In this paper, the authors introduce the concept of soft directed hypergraphs, which represent a further extension of soft graph theory. They also investigate various operations on soft directed hypergraphs, aiming to elucidate their properties.

2. Preliminaries

For basic concepts of a directed hypergraph, we refer [1,4,8]. “A directed hypergraph Δ=(Γ,Ξ) consists of a vertex set Γ and a set of directed hyperedges or hyperarcs Ξ={e=(T(e),H(e))|T(e)Γ and H(e)Γ}, where T(e)ϕ and H(e)ϕ. The sets T(e) and H(e) are called tail and head of the hyperarc e, respectively. A directed hypergraph is called k-uniform if |T(e)|=|H(e)|=k for all eΞ. Two hyperarcs e and e are said to be parallel if T(e)=T(e) and H(e)=H(e). A hyperarc e is said to be a loop if T(e)=H(e). A directed hypergraph Δ=(Γ,Ξ) is called simple if it has no parallel hyperarcs and loops. A directed hypergraph is called trivial if |Γ|=1 and Ξ=ϕ. If the two vertices u and v of Δ are such that uT(e) and vH(e) then we say that v is adjacent from u or u is adjacent to v. The indegree of a vertex v in Δ, denoted by d(v) is the number of hyperarcs that contain v in their head. The outdegree of a vertex v in Δ, denoted by d+(v) is the number of hyperarcs that contain v in their tail. A directed hypergraph Δ=(Γ,Ξ) is a weak subhypergraph of the directed hypergraph Δ=(Γ,Ξ) if ΓΓ and Ξ consists of hyperarcs e with T(e)={v|vT(e)Γ} and H(e)={v|vH(e)Γ} for some eΞ. A directed hypergraph Δ=(Γ,Ξ) is a weak induced subhypergraph of the directed hypergraph Δ=(Γ,Ξ) if ΓΓ and hyperarc set Ξ={(T(e)Γ,H(e)Γ)|eΞandT(e)ΓϕandH(e)Γϕ}.”

In 1999 Molodtsov [27] initiated the concept of soft sets. Let U be an initial universe set and let Π be a set of parameters. A pair (F,Π) is called a soft set (over U) if and only F is a mapping of Π into the set of all subsets of the set U. That is, F:ΠP(U).

3. Soft directed hypergraphs

Definition 3.1 Let Δ=(Γ,Ξ) be a simple directed hypergraph with vertex set Γ and directed hyperedge(hyperarc) set Ξ. Then a e=(T(e),H(e)) where T(e) and H(e) are nonempty subsets of Γ, is said to be a subhyperarc of Δ if there exists a hyperarc e in Δ such that T(e)T(e) and H(e)H(e). We also say that e is a subhyperarc of e. Clearly, a hyperarc is a subhyperarc of itself. e is said to be a proper subhyperarc of e if either T(e)T(e) or H(e)H(e).
Definition 3.2 Consider Δ=(Γ,Ξ) as a simple directed hypergraph comprising a vertex set Γ and a set of directed hyperedges (or hyperarcs) Ξ, and let Π denote any nonempty set. Denote Ξs as the collection of all subhyperarcs of Δ. Let R represent an arbitrary relation between elements from Π and those from Γ. That is RΠ×Γ. A mapping Ω:ΠP(Γ) can be defined as Ω(π)={vΓ:πRv} where P(Γ) denotes the powerset of Γ . Also define a mapping Y:ΠP(Ξs) by Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ} where P(Ξs) denotes the powerset of Ξs. The pair (Ω,Π) is a soft set over Γ and the pair (Ψ,Π) is a soft set over Ξs. Then the 4 -tuple Δ=(Δ,Ω,Ψ,Π) is called a soft directed hypergraph if it satisfies the following conditions:
  1. Δ=(Γ,Ξ) is a simple directed hypergraph having vertex set Γ and hyperarc set Ξ,

  2. Π is a nonempty set of parameters,

  3. (Ω,Π) is a soft set over Γ,

  4. (Ψ,Π) is a soft set over Ξs,

  5. (e)(Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ.

If we represent (Ω(π),Ψ(π)) by Z(π), then the soft directed hypergraph Δ is also given by {Z(π):πΠ}. Then Z(π) corresponding to a parameter π in Π is called a directed hyperpart or simply dh-part of the soft directed hypergraph Δ.

Example 3.3 Consider a directed hypergraph Δ=(Γ,Ξ) given in Figure 1.
Figure 1 Directed hypergraph Δ=(Γ,Ξ)

Let Π={v2,v10}Γ be a parameter set. Define a function X:ΠP(Γ) defined by Ω(π)={vΓ:πRvv=π or v is adjacent from π or v is adjacent to π} for all πP. That is, Ω(v2)={v1,v2,v3,v7,v9} and Ω(v10)={v5,v10,v11}. Then (Ω,Π) is a soft set over Γ. Define another function Ψ:ΠP(Ξs) defined by Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. That is, Ψ(v2)={({v1,v3},{v2}),({v2},{v7,v9})} and v10)={({v5},{v10}),({v10},{v11})}. Then (Ψ,Π) is a soft set over Ξs. Also Z(v2)=(Ω(v2),Ψ(v2)) and Z(v10)=(Ω(v10),Ψ(v10)) are weak induced subhypergraphs of Δ as shown in Figure 2. Hence Δ={Z(v2),Z(v10)} is a soft directed hypergraph of Δ.

Figure 2 Soft directed hypergraph Δ={Z(v2),Z(v10)}
Definition 3.4 Let Δ=(Γ,Ξ) be a simple hypergraph having vertex set Γ and hyperarc set Ξ. Also let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ. Then Δ2 is a soft weak induced subhypergraph of Δ1 if
  1. Π2Π1,

  2. Z2(π)=(Ω2(π),Ψ2(π)) is a weak induced subhypergraph of Z1(π)=(Ω1(π),Ψ1(π)) for all πΠ2.

Example 3.5 Consider a directed hypergraph Δ=(Γ,Ξ) given in Figure 3.
Figure 3 Directed hypergraph Δ=(Γ,Ξ)

Let Π1={v3,v7}Γ be a parameter set. Define a function Ω1:Π1P(Γ) defined by Ω1(π)={vΓ:πRvv=π or v is adjacent from π or v is adjacent to π} for all πΠ1. That is, Ω1(v3)={v3,v4,v5,v9,v11} and Ω1(v7)={v6,v7,v9,v10,v12}.

Then (Ω1,Π1) is a soft set over Γ. Define another function Ψ1:Π1P(Ξs) defined by Ψ1(π)={(T(e)Ω1(π),H(e)Ω1(π))|eΞandT(e)Ω1(π)ϕandH(e)Ω1(π)ϕ}. That is, Ψ1(v3)={({v11},{v3}),({v3},{v4,v5,v9})} and Ψ1(v7)={({v6,v9},{v7}),({v10},{v7}),({v7},{v12})}. Then (Ψ1,Π1) is a soft set over Ξs. Also Z1(v3)=(Ω1(v3),Ψ1(v3)) and Z1(v7)=(Ω1(v7),Ψ1(v7)) are weak induced subhypergraphs of Δ as shown in Figure 4. Hence Δ1={Z1(v3),Z1(v7)} is a soft directed hypergraph of Δ.

Figure 4 Soft Directed hypergraph Δ1={Z1(v3),Z1(v7)}

Let Π2={v7}Γ be another parameter set. Define a function Ω2:Π2P(Γ) defined by Ω2(π)={vΓ:πRvv=π or v is adjacent to π} for all πΠ2. That is, Ω2(v7)={v6,v7,v9,v10}. Then (Ω2,Π2) is a soft set over Γ. Define another function Ψ2:Π2P(Ξs) defined by Ψ2(π)={(T(e)Ω2(π),H(e)Ω2(π))|eΞandT(e)Ω2(π)ϕandH(e)Ω2(π)ϕ}. That is, Ψ2(v7)={({v6,v9},{v7}),({v10},{v7})}. Then (Ψ2,Π2) is a soft set over Ξs. Also Z2(v7)=(Ω2(v7),Ψ2(v7)) is a weak induced subhypergraph of Δ as shown in Figure 5. Hence Δ2={Z2(v7)} is a soft directed hypergraph of Δ.

Figure 5 Soft Directed hypergraph Δ2={Z2(v7)}

Here Δ2 is a soft weak induced subhypergraph of Δ1 since

  1. Π2Π1,

  2. Z2(v7)=(Ω2(v7),Ψ2(v7)) is a weak induced subhypergraph of Z1(v7)=(Ω1(v7),Ψ1(v7)).

4. Extended union of two soft directed hypergraphs

Definition 4.1. Let Δ=(Γ,Ξ) be a simple directed hypergraph having vertex set Γ and hyperarc set Ξ. Also let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ . Then the \textit{extended union} of Δ1 and Δ2 denoted by Δ1EΔ2 is defined as Δ1EΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ, Ω(π)={Ω1(π),ifπΠ1Π2,Ω2(π),ifπΠ2Π1,Ω1(π)Ω2(π),ifπΠ1Π2. and Ψ(π)={Ψ1(π),ifπΠ1Π2,Ψ2(π),ifπΠ2Π1,{(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ},ifπΠ1Π2. If Z(π)=(Ω(π),Ψ(π)),πΠ, then Δ1EΔ2={Z(π):πΠ}.
Example 4.2. Consider a simple directed hypergraph Δ=(Γ,Ξ) given in Figure 6.
Figure 6 Directed hypergraph Δ=(Γ,Ξ)

Let Π1={v7,v9}Γ be a parameter set. Define a function Ω1:Π1P(Γ) defined by Ω1(π)={vΓ:πRvv=π or v is adjacent from π or v is adjacent to π}, for all πΠ1. That is, Ω1(v7)={v1,v2,v7,v9,v12} and Ω1(v9)={v3,v6,v7,v9,v14}. Then (Ω1,Π1) is a soft set over Γ. Define another function Ψ1:Π1P(Ξs) defined by Ψ1(π)={(T(e)Ω1(π),H(e)Ω1(π))|eΞandT(e)Ω1(π)ϕandH(e)Ω1(π)ϕ}. That is, Ψ1(v7)={({v1,v12},{v7}),({v2,v9},{v7})} and Ψ1(v9)={({v9},{v6,v7}),({v3},{v9}),({v9},{v14})}. Then (Ψ1,Π1) is a soft set over Ξs. Also Z1(v7)=(Ω1(v7),Ψ1(v7)) and Z1(v9)=(Ω1(v9),Ψ1(v9)) are weak induced subhypergraphs of Δ as shown in Figure 7.

Hence Δ1={Z1(v7),Z1(v9)} is a soft directed hypergraph of Δ.

Figure 7 Soft Directed hypergraph Δ1={Z1(v7),Z1(v9)}

Let Π2={v9,v15}Γ be another parameter set. Define a function Ω2:Π2P(Γ) defined by Ω2(π)={vΓ:πRvv=π or v is adjacent from π}, for all πΠ2. That is, Ω2(v9)={v6,v7,v9,v14} and Ω2(v15)={v3,v10,v13,v14,v15}. Then (Ω2,Π2) is a soft set over Γ. Define another function Ψ2:Π2P(Ξs) defined by Ψ2(π)={(T(e)Ω2(π),H(e)Ω2(π))|eΞandT(e)Ω2(π)ϕandH(e)Ω2(π)ϕ}. That is, Ψ2(v9)={({v9},{v6,v7}),({v9},{v14})} and Ψ2(v15)={({v15},{v3,v10,v14}),({v15},{v13})}. Then (Ψ2,Π2) is a soft set over Ξs. Also Z2(v9)=(Ω2(v9),Ψ2(v9)) and Z2(v15)=(Ω2(v15),Ψ2(v15)) are weak induced subhypergraphs of Δ as shown in Figure 8.

Hence Δ2={Z2(v9),Z2(v15)} is a soft directed hypergraph of Δ.

Figure 8 Soft Directed Hypergraph Δ2={Z2(v9),Z2(v15)}

The extended union of two soft directed hypergraphs Δ1 and Δ2 is Δ=Δ1EΔ2=(Δ,Ω,Ψ,Π) where Π=Π1Π2={v7,v9,v15}. Also Ω(v7)=Ω1(v7)={v1,v2,v7,v9,v12}, Ψ(v7)=Ψ1(v7)={({v1,v12},{v7}),({v2,v9},{v7})}, Ω(v9)=Ω1(v9)Ω2(v9)=Ω1(v9)={v3,v6,v7,v9,v14}, Ψ(v9)={(T(e)Ω(v9),H(e)Ω(v9))|eΞandT(e)Ω(v9)ϕandH(e)Ω(v9)ϕ}={({v9},{v6,v7}),({v3},{v9}),({v9},{v14})}, Ω(v15)=Ω2(v15)={v3,v10,v13,v14,v15} and Ψ(v15)=Ψ2(v15)={({v15},{v3,v10,v14}),({v15},{v13})}. Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. Also Z(v7)=(Ω(v7),Ψ(v7)),Z(v9)=(Ω(v9),Ψ(v9)) and Z(v15)=(Ω(v15),Ψ(v15)) are weak induced subhypergraphs of Δ. Hence Δ1EΔ2={Z(v7),Z(v9),Z(v15)} is a soft directed hypergrah of Δ and is given in Figure 9.

Figure 9 Δ1EΔ2={Z(v7),Z(v9),Z(v15)}
Theorem 4.3. Let Δ=(Γ,Ξ) be a simple directed hypergraph having vertex set Γ and hyperarc set Ξ. Also let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ . Then their extended union Δ1EΔ2 is also a soft directed hypergraph of Δ.

Proof. The extended union of Δ1 and Δ2 is given by Δ1EΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ,<Ω(π)={Ω1(π),ifπΠ1Π2,Ω2(π),ifπΠ2Π1,Ω1(π)Ω2(π),ifπΠ1Π2. and Ψ(π)={Ψ1(π),ifπΠ1Π2,Ψ2(π),ifπΠ2Π1,{(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ},ifπΠ1Π2..

That is, in Δ1EΔ2, Π=Π1Π2 is a parameter set, Ω is a mapping from Π to P(Γ) and Ψ is a mapping from Π to P(Ξs). Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. When πΠ1Π2, the corresponding dh-part Z(π) of Δ1EΔ2 is Z(π)=(Ω1(π),Ψ1(π)). This is a weak induced subhypergraph of Δ since Δ1 is a soft directed hypergraph of Δ. When πΠ2Π1, the corresponding dh-part of Δ1EΔ2 is Z(π)=(Ω2(π),Ψ2(π)). This is a weak induced subhypergraph of Δ since Δ2 is a soft directed hypergraph of Δ. When πΠ1Π2 , the corresponding dh-part of Δ1EΔ2 is Z(π)=(Ω(π),Ψ(π)) where Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. We have Ω1(π)Ω2(π)Γ and each hyperarc in Ψ(π) is a subhyperarc of Δ for all πΠ1Π2. So Z(π) is a weak induced subhypergraph of Δ for all πΠ1Π2. That is, Z(π)=(Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ=Π1Π2. That is, Δ1EΔ2=(Δ,Ω,Ψ,Π) is a soft directed hypergraph of Δ since the following conditions are satisfied:

  1. Δ=(Γ,Ξ) is a simple directed hypergraph,

  2. Π=Π1Π2 is a nonempty set of parameters,

  3. (Ω,Π) is a soft set over Γ,

  4. (Ψ,Π) is a soft set over Ξs,

  5. (Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ=Π1Π2.

◻

5. Extended intersection of two soft directed hypergraphs

Definition 5.1. Consider Δ=(Γ,Ξ) as a simple directed hypergraph with a vertex set Γ and a set of hyperarcs Ξ. Let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) represent two soft directed hypergraphs derived from Δ, with the condition that Ω1(π)Ω2(π) for all πΠ1Π2. Then, the extended intersection of Δ1 and Δ2, denoted by Δ1EΔ2, is defined as Δ1EΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ,

Ω(π)={Ω1(π),ifπΠ1Π2,Ω2(π),ifπΠ2Π1,Ω1(π)Ω2(π),ifπΠ1Π2. and Ψ(π)={Ψ1(π),ifπΠ1Π2,Ψ2(π),ifπΠ2Π1,{(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕ$and$H(e)Ω(π)ϕ},ifπΠ1Π2.. If Z(π)=(Ω(π),Ψ(π)),πΠ, then Δ1EΔ2={Z(π):πΠ}.
Example 5.2. Examine a simple directed hypergraph Δ=(Γ,Ξ) depicted in Figure 6, along with its corresponding soft directed hypergraphs Δ1 illustrated in Figure 7 and Δ2 depicted in Figure 8. The extended intersection of these two soft directed hypergraphs Δ1 and Δ2 is Δ=Δ1EΔ2=(Δ,Ω,Ψ,Π) where Π=Π1Π2={v7,v9,v15}. Also Ω(v7)=Ω1(v7)={v1,v2,v7,v9,v12}, Ψ(v7)=Ψ1(v7)={({v1,v12},{v7}),({v2,v9},{v7})}, Ω(v9)=Ω1(v9)Ω2(v9)=Ω2(v9)={v6,v7,v9,v14}, Ψ(v9)={(T(e)Ω(v9),H(e)Ω(v9))|eΞandT(e)Ω(v9)ϕandH(e)Ω(v9)ϕ}={({v9},{v6,v7}),({v9},{v14})}, Ω(v15)=Ω2(v15)={v3,v10,v13,v14,v15} and Ψ(v15)=Ψ2(v15)={({v15},{v3,v10,v14}),({v15},{v13})}. Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. Also Z(v7)=(Ω(v7),Ψ(v7)),Z(v9)=(Ω(v9),Ψ(v9)) and Z(v15)=(Ω(v15),Ψ(v15)) are weak induced subhypergraphs of Δ. Hence Δ1EΔ2={Z(v7),Z(v9),Z(v15)} is a soft directed hypergrah of Δ and is given in Figure 10.

Figure 10 Δ1EΔ2={Z(v7),Z(v9),Z(v15)}
Theorem 5.3. Let Δ=(Γ,Ξ) be a simple directed hypergraph having vertex set Γ and hyperarc set Ξ. Also let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft hypergraphs of Δ such that Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then their extended intersection Δ1EΔ2 is also a soft directed hypergraph of Δ.

Proof. The extended intersection of Δ1 and Δ2 is given by Δ1EΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ,

Ω(π)={Ω1(π),ifπΠ1Π2,Ω2(π),ifπΠ2Π1,Ω1(π)Ω2(π),ifπΠ1Π2. and Ψ(π)={Ψ1(π),ifπΠ1Π2,Ψ2(π),ifπΠ2Π1,{(T(e)Ω(π),H(e)Ω(π))|eΞ$and$T(e)Ω(π)ϕandH(e)Ω(π)ϕ},ifπΠ1Π2..

That is, in Δ1EΔ2, Π=Π1Π2 is a parameter set, Ω is a mapping from Π to P(Γ) and Ψ is a mapping from Π to P(Ξs). Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. When πΠ1Π2, the corresponding dh-part Z(π) of Δ1EΔ2 is Z(π)=(Ω1(π),Ψ1(π)). This is a weak induced subhypergraph of Δ since Δ1 is a soft directed hypergraph of Δ. When πΠ2Π1, the corresponding dh-part of Δ1EΔ2 is Z(π)=(Ω2(π),Ψ2(π)). This is a weak induced subhypergraph of Δ since Δ2 is a soft directed hypergraph of Δ. When πΠ1Π2 , the corresponding dh-part of Δ1EΔ2 is Z(π)=(Ω(π),Ψ(π)) where Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. We have Ω1(π)Ω2(π)Γ and each hyperarc in Ψ(π) is a subhyperarc of Δ for all πΠ1Π2. So Z(π) is a weak induced subhypergraph of Δ for all πΠ1Π2. That is, Z(π)=(Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ, for all πΠ=Π1Π2. That is, Δ1EΔ2=(Δ,Ω,Ψ,Π) is a soft directed hypergraph of Δ since the following conditions are satisfied:

  1. Δ=(Γ,Ξ) is a simple directed hypergraph,

  2. Π=Π1Π2 is a nonempty set of parameters,

  3. (Ω,Π) is a soft set over Γ,

  4. (Ψ,Π) is a soft set over Ξs,

  5. (Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ.

◻

Theorem 5.4. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then Δ1EΔ2 is a soft weak induced subhypergraph of Δ1EΔ2.

Proof. By Theorems 4.3 and 5.3, we have Δ1EΔ2 and Δ1EΔ2 are soft directed hypergraphs of Δ. Assume that Δ1EΔ2=ΔEU=(Δ,ΩEU,ΨEU,ΠEU) and Δ1EΔ2=ΔEI=(Δ,ΩEI,ΨEI,ΠEI). By the definitions of extended union and the extended intersection of two soft directed hypergraphs, ΠEU=ΠEI=Π1Π2. Therefore we have ΠEIΠEU.

We divide the parameter set ΠEI=Π1Π2 into three parts: (i) Π1Π2 (ii) Π2Π1 (iii) Π1Π2. We consider the three cases one by one.

  1. If πΠ1Π2, the corresponding dh-parts ZEI(π)=(ΩEI(π),ΨEI(π)) and ZEU(π)=(ΩEU(π),ΨEU(π)) of ΔEI and ΔEU respectively are equal to Z1(π)=(Ω1(π),Ψ1(π)). That is, ZEI(π) is a weak induced subhypergraph of ZEU(π),πΠ1Π2, since both dh-parts are identical.

  2. If πΠ2Π1, the corresponding dh-parts ZEI(π)=(ΩEI(π),ΨEI(π)) and ZEU(π)=(ΩEU(π),ΨEU(π)) of ΔEI and ΔEU respectively are equal to Z2(π)=(Ω2(π),Ψ2(π)). That is, ZEI(π) is a weak induced subhypergraph of ZEU(π),πΠ2Π1, since both dh-parts are identical.

  3. If πΠ1Π2, ZEI(π)=(ΩEI(π),ΨEI(π)), where ΩEI(π)=Ω1(π)Ω2(π) and ΨEI(π)={(T(e)ΩEI(π),H(e)ΩEI(π))|eΞandT(e)ΩEI(π)ϕandH(e)ΩEI(π)ϕ} and ZEU(π)=(ΩEU(π),ΨEU(π)), where ΩEU(π)=Ω1(π)Ω2(π) and ΨEU(π)={(T(e)ΩEU(π),H(e)ΩEU(π))|eΞandT(e)ΩEU(π)ϕandH(e)ΩEU(π)ϕ}. Clearly ΩEI(π)ΩEU(π) and each hyperarc present in ΨEI(π) is a subhyperarc of a hyperarc present in ΨEU(π). So ZEI(π) is a weak induced subhypergraph of ZEU(π),πΠ2Π1.

That is, we have

  1. ΠEIΠEU,

  2. For all πΠEI, ZEI(π)=(ΩEI(π),ΨEI(π)) is a weak induced subhypergraph of ZEU(π)=(ΩEU(π),ΨEU(π)).

Hence Δ1EΔ2 is a soft weak induced subhypergraph of Δ1EΔ2. ◻

6. Restricted union of two soft directed hypergraphs

Definition 6.1. Consider Δ=(Γ,Ξ) as a simple directed hypergraph with a vertex set Γ and a set of hyperarcs Ξ. Let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) represent two soft directed hypergraphs derived from Δ such that Π1Π2. Then, the restricted union of Δ1 and Δ2, denoted by Δ1RΔ2, is defined as Δ1RΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ, Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. If Z(π)=(Ω(π),Ψ(π)),πΠ, then Δ1RΔ2={Z(π):πΠ}.

Example 6.2. Examine a simple directed hypergraph Δ=(Γ,Ξ) as illustrated in Figure 6, along with its soft directed hypergraphs Δ1 depicted in Figure 7 and Δ2 shown in Figure 8. The restricted union of these two soft directed hypergraphs Δ1 and Δ2 is Δ=Δ1RΔ2=(Δ,Ω,Ψ,Π) where Π=Π1Π2={v9}. Also Ω(v9)=Ω1(v9)Ω2(v9)={v3,v6,v7,v9,v14}, Ψ(v9)={(T(e)Ω(v9),H(e)Ω(v9))|eΞandT(e)Ω(v9)ϕandH(e)Ω(v9)ϕ}={({v9},{v6,v7}),({v3},{v9}),({v9},{v14})} Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. Also Z(v9)=(Ω(v9),Ψ(v9)) is a weak induced subhypergraph of Δ. Hence Δ1RΔ2={Z(v9)} is a soft directed hypergrah of Δ and is given in Figure 11.

Figure 11 Δ1RΔ2={Z(v9)}
Theorem 6.3. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ. Then their restricted union Δ1RΔ2 is also a soft directed hypergraph of Δ.

Proof. The restricted union Δ1RΔ2 is defined as Δ1RΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2ϕ is the parameter set and for all πΠ, Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. Here Ω is a mapping from Π to P(Γ) and Ψ is a mapping from Π to P(Ξs). Also (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. When πΠ=Π1Π2 , the corresponding dh-part of Δ1RΔ2 is Z(π)=(Ω(π),Ψ(π)) where Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. We have Ω1(π)Ω2(π)Γ and each hyperarc in Ψ(π) is a subhyperarc of Δ for all πΠ=Π1Π2. So Z(π)=(Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ=Π1Π2. That is, Δ1RΔ2=(Δ,Ω,Ψ,Π) is a soft directed hypergraph of Δ since all the conditions for a soft directed hypergraph are satisfied. ◻

Theorem 6.4. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ. Then Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2.

Proof. By Theorems 4.3 and 6.3, we have Δ1EΔ2 and Δ1RΔ2 are soft directed hypergraphs of Δ. Assume that Δ1EΔ2=ΔEU=(Δ,ΩEU,ΨEU,ΠEU) and Δ1RΔ2=ΔRU=(Δ,ΩRU,ΨRU,ΠRU). By the definitions of extended union and restricted union of two soft directed hypergraphs, the parameter set ΠEU of ΔEU is Π1Π2 and the parameter set ΠRU of ΔRU is Π1Π2. Clearly we have ΠRUΠEU since Π1Π2Π1Π2. If πΠRU=Π1Π2, ZRU(π)=(ΩRU(π),ΨRU(π)), where ΩRU(π)=Ω1(π)Ω2(π) and ΨRU(π)={(T(e)ΩRU(π),H(e)ΩRU(π))|eΞandT(e)ΩRU(π)ϕandH(e)ΩRU(π)ϕ} and ZEU(π)=(ΩEU(π),ΨEU(π)), where ΩEU(π)=Ω1(π)Ω2(π) and ΨEU(π)={(T(e)ΩEU(π),H(e)ΩEU(π))|eΞandT(e)ΩEU(π)ϕandH(e)ΩEU(π)ϕ}. Clearly ZRU(π) is a weak induced subhypergraph of ZEU(π),πΠRU=Π1Π2, since both dh-parts are identical. That is, we have

  1. ΠRUΠEU,

  2. For all πΠRU, ZRU(π)=(ΩRU(π),ΨRU(π)) is a weak induced subhypergraph of ZEU(π)=(ΩEU(π),ΨEU(π)).

Hence Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2. ◻

7. Restricted intersection of two soft directed hypergraphs

Definition 7.1. Let Δ=(Γ,Ξ) be a simple directed hypergraph having vertex set Γ and hyperarc set Ξ. Also let Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ and Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then the restricted intersection of Δ1 and Δ2 denoted by Δ1RΔ2 is defined as Δ1RΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2 and for all πΠ, Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. If Z(π)=(Ω(π),Ψ(π)),πΠ, then Δ1RΔ2={Z(π):πΠ}.

Example 7.2. Take into account a simple directed hypergraph Δ=(Γ,Ξ) as depicted in Figure 6, along with its soft directed hypergraphs Δ1 presented in Figure 7 and Δ2 illustrated in Figure 8, correspondingly. The restricted intersection of these two soft directed hypergraphs Δ1 and Δ2 is Δ=Δ1RΔ2=(Δ,Ω,Ψ,Π) where Π=Π1Π2={v9}. Also Ω(v9)=Ω1(v9)Ω2(v9)={v6,v7,v9,v14}, Ψ(v9)={(T(e)Ω(v9),H(e)Ω(v9))|eΞandT(e)Ω(v9)ϕandH(e)Ω(v9)ϕ}={({v9},{v6,v7}),({v9},{v14})}. Here (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. Also Z(v9)=(Ω(v9),Ψ(v9)) is a weak induced subhypergraph of Δ. Hence Δ1RΔ2={Z(v9)} is a soft directed hypergraph of Δ and is given in Figure 12.

Figure 12 Δ1RΔ2={Z(v9)}
Theorem 7.3. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ and Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then their restricted intersection Δ1RΔ2 is also a soft directed hypergraph of Δ.

Proof. The restricted intersection Δ1RΔ2 is defined as Δ1RΔ2=Δ=(Δ,Ω,Ψ,Π), where Π=Π1Π2ϕ is the parameter set and for all πΠ, Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. Here Ω is a mapping from Π to P(Γ) and Ψ is a mapping from Π to P(Ξs). Also (Ω,Π) is a soft set over Γ and (Ψ,Π) is a soft set over Ξs. When πΠ=Π1Π2 , the corresponding dh-part of Δ1RΔ2 is Z(π)=(Ω(π),B(π)) where Ω(π)=Ω1(π)Ω2(π) and Ψ(π)={(T(e)Ω(π),H(e)Ω(π))|eΞandT(e)Ω(π)ϕandH(e)Ω(π)ϕ}. We have Ω1(π)Ω2(π)Γ and each hyperarc in Ψ(π) is a subhyperarc of Δ for all πΠ=Π1Π2. So Z(π)=(Ω(π),Ψ(π)) is a weak induced subhypergraph of Δ for all πΠ=Π1Π2. That is, Δ1RΔ2=(Δ,Ω,Ψ,Π) is a soft directed hypergraph of Δ since all the conditions for a soft directed hypergraph are satisfied. ◻

Theorem 7.4. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ and Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2.

Proof. By Theorems 5.3 and 7.3, we have Δ1EΔ2 and Δ1RΔ2 are soft directed hypergraphs of Δ. Assume that Δ1EΔ2=ΔEI=(Δ,ΩEI,ΨEI,ΠEI) and Δ1RΔ2=ΔRI=(Δ,ΩRI,ΨRI,ΠRI). By the definitions of extended intersection and restricted intersection of two soft directed hypergraphs, the parameter set ΠEI of ΔEI is Π1Π2 and the parameter set ΠRI of ΔRI is Π1Π2. Clearly we have ΠRIΠEI since Π1Π2Π1Π2. If πΠRI=Π1Π2, ZRI(π)=(ΩRI(π),ΨRI(π)), where ΩRI(π)=Ω1(π)Ω2(π) and ΨRI(π)={(T(e)ΩRI(π),H(e)ΩRI(π))|eΞandT(e)ΩRI(π)ϕandH(e)ΩRI(π)ϕ} and ZEI(π)=(ΩEI(π),ΨEI(π)), where ΩEI(π)=Ω1(π)Ω2(π) and ΨEI(π)={(T(e)ΩEI(π),H(e)ΩEI(π))|eΞandT(e)ΩEI(π)ϕandH(e)ΩEI(π)ϕ}. Clearly ZRI(π) is a weak induced subhypergraph of ZEI(π),πΠRI=Π1Π2, since both dh-parts are identical. That is, we have

  1. ΠRIΠEI,

  2. For all πΠRI, ZRI(π)=(ΩRI(π),ΩRI(π)) is a weak induced subhypergraph of ZEI(π)=(ΩEI(π),ΨEI(π)).

Hence Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2. ◻

Theorem 7.5. Let Δ=(Γ,Ξ) be a simple directed hypergraph and Δ1=(Δ,Ω1,Ψ1,Π1) and Δ2=(Δ,Ω2,Ψ2,Π2) be two soft directed hypergraphs of Δ such that Π1Π2ϕ and Ω1(π)Ω2(π)ϕ for all πΠ1Π2. Then Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2.

Proof. By Theorems 4.3 and 7.3, we have Δ1EΔ2 and Δ1RΔ2 are soft directed hypergraphs of Δ. Assume that Δ1EΔ2=ΔEU=(Δ,ΩEU,ΨEU,ΠEU) and Δ1RΔ2=ΔRI=(Δ,ΩRI,ΨRI,ΠRI). By the definitions of extended union and restricted intersection of two soft directed hypergraphs, the parameter set ΠEU of ΔEU is Π1Π2 and the parameter set ΠRI of ΔRI is Π1Π2. Clearly we have ΠRIΠEU since Π1Π2Π1Π2. If πΠRI=Π1Π2, ZRI(π)=(ΩRI(π),ΨRI(π)), where ΩRI(π)=Ω1(π)Ω2(π) and ΨRI(π)={(T(e)ΩRI(π),H(e)ΩRI(π))|eΞandT(e)ΩRI(π)ϕandH(e)ΩRI(π)ϕ} and ZEU(π)=(ΩEU(π),ΨEU(π)), where ΩEU(π)=Ω1(π)Ω2(π) and ΨEU(π)={(T(e)ΩEU(π),H(e)ΩEU(π))|eΞandT(e)ΩEU(π)ϕandH(e)ΩEU(π)ϕ}. Clearly ZRI(π) is a weak induced subhypergraph of ZEU(π),πΠRI=Π1Π2. That is, we have

  1. ΠRIΠEU,

  2. For all πΠRI, ZRI(π)=(ΩRI(π),ΨRI(π)) is a weak induced subhypergraph of ZEU(π)=(ΩEU(π),ΨEU(π)).

Hence Δ1RΔ2 is a soft weak induced subhypergraph of Δ1EΔ2. ◻

8. Conclusion

The introduction of soft directed hypergraphs stemmed from incorporating soft set principles into directed hypergraphs. Through parameterization, soft directed hypergraphs generate a sequence of descriptions for intricate relations depicted by directed hypergraphs. Undoubtedly, the incorporation of parameterization tools renders soft directed hypergraphs a pivotal component in the realm of directed hypergraph theory.

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