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.
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 consists of a vertex set and a set of directed hyperedges or hyperarcs and , where and . The sets and are called tail and head of the hyperarc , respectively. A directed hypergraph is called k-uniform if for all . Two hyperarcs and are said to be parallel if and . A hyperarc is said to be a loop if . A directed hypergraph is called simple if it has no parallel hyperarcs and loops. A directed hypergraph is called trivial if and . If the two vertices and of are such that and then we say that is adjacent from or is adjacent to. The indegree of a vertex in , denoted by is the number of hyperarcs that contain in their head. The outdegree of a vertex in , denoted by is the number of hyperarcs that contain in their tail. A directed hypergraph is a weak subhypergraph of the directed hypergraph if and consists of hyperarcs with and for some . A directed hypergraph is a weak induced subhypergraph of the directed hypergraph if and hyperarc set andand.”
In 1999 Molodtsov [27] initiated the concept of soft sets. Let be an initial universe set and let be a set of parameters. A pair is called a soft set (over ) if and only is a mapping of into the set of all subsets of the set . That is, .
3. Soft directed hypergraphs
Definition 3.1 Let be a simple directed hypergraph with vertex set and directed hyperedge(hyperarc) set . Then a where and are nonempty subsets of , is said to be a subhyperarc of if there exists a hyperarc in such that and . We also say that is a subhyperarc of . Clearly, a hyperarc is a subhyperarc of itself. is said to be a proper subhyperarc of if either or .
Definition 3.2 Consider as a simple directed hypergraph comprising a vertex set and a set of directed hyperedges (or hyperarcs) , and let denote any nonempty set. Denote as the collection of all subhyperarcs of . Let represent an arbitrary relation between elements from and those from . That is . A mapping can be defined as where denotes the powerset of . Also define a mapping by andand where denotes the powerset of . The pair is a soft set over and the pair is a soft set over . Then the 4 -tuple is called a soft directed hypergraph if it satisfies the following conditions:
is a simple directed hypergraph having vertex set and hyperarc set ,
is a nonempty set of parameters,
is a soft set over ,
is a soft set over ,
(e) is a weak induced subhypergraph of for all .
If we represent by , then the soft directed hypergraph is also given by . Then corresponding to a parameter in is called a directed hyperpart or simply dh-part of the soft directed hypergraph .
Example 3.3 Consider a directed hypergraph given in Figure 1.
Figure 1 Directed hypergraph
Let be a parameter set. Define a function defined by or is adjacent from or is adjacent to } for all . That is, and . Then is a soft set over . Define another function defined by andand. That is, and . Then is a soft set over . Also and are weak induced subhypergraphs of as shown in Figure 2. Hence is a soft directed hypergraph of .
Figure 2 Soft directed hypergraph
Definition 3.4 Let be a simple hypergraph having vertex set and hyperarc set . Also let and be two soft directed hypergraphs of . Then is a soft weak induced subhypergraph of if
,
is a weak induced subhypergraph of for all .
Example 3.5 Consider a directed hypergraph given in Figure 3.
Figure 3 Directed hypergraph
Let be a parameter set. Define a function defined by or is adjacent from or is adjacent to } for all . That is, and .
Then is a soft set over . Define another function defined by andand. That is, and . Then is a soft set over . Also and are weak induced subhypergraphs of as shown in Figure 4. Hence is a soft directed hypergraph of .
Figure 4 Soft Directed hypergraph
Let be another parameter set. Define a function defined by or is adjacent to } for all . That is, . Then is a soft set over . Define another function defined by andand. That is, . Then is a soft set over . Also is a weak induced subhypergraph of as shown in Figure 5. Hence is a soft directed hypergraph of .
Figure 5 Soft Directed hypergraph
Here is a soft weak induced subhypergraph of since
,
is a weak induced subhypergraph of .
4. Extended union of two soft directed hypergraphs
Definition 4.1. Let be a simple directed hypergraph having vertex set and hyperarc set . Also let and be two soft directed hypergraphs of . Then the \textit{extended union} of and denoted by is defined as , where and for all , and If , then
Example 4.2. Consider a simple directed hypergraph given in Figure 6.
Figure 6 Directed hypergraph
Let be a parameter set. Define a function defined by or is adjacent from or is adjacent to }, for all . That is, and . Then is a soft set over . Define another function defined by andand. That is, and . Then is a soft set over . Also and are weak induced subhypergraphs of as shown in Figure 7.
Hence is a soft directed hypergraph of .
Figure 7 Soft Directed hypergraph
Let be another parameter set. Define a function defined by or is adjacent from }, for all . That is, and . Then is a soft set over . Define another function defined by andand. That is, and . Then is a soft set over . Also and are weak induced subhypergraphs of as shown in Figure 8.
Hence is a soft directed hypergraph of .
Figure 8 Soft Directed Hypergraph
The extended union of two soft directed hypergraphs and is where . Also , , , andand, and . Here is a soft set over and is a soft set over . Also and are weak induced subhypergraphs of . Hence is a soft directed hypergrah of and is given in Figure 9.
Figure 9
Theorem 4.3. Let be a simple directed hypergraph having vertex set and hyperarc set . Also let and be two soft directed hypergraphs of . Then their extended union is also a soft directed hypergraph of .
Proof. The extended union of and is given by , where and for all ,< and
That is, in , is a parameter set, is a mapping from to and is a mapping from to . Here is a soft set over and is a soft set over . When , the corresponding dh-part of is . This is a weak induced subhypergraph of since is a soft directed hypergraph of . When , the corresponding dh-part of is . This is a weak induced subhypergraph of since is a soft directed hypergraph of . When , the corresponding dh-part of is where and andand. We have and each hyperarc in is a subhyperarc of for all . So is a weak induced subhypergraph of for all . That is, is a weak induced subhypergraph of for all . That is, is a soft directed hypergraph of since the following conditions are satisfied:
is a simple directed hypergraph,
is a nonempty set of parameters,
is a soft set over ,
is a soft set over ,
is a weak induced subhypergraph of for all .
5. Extended
intersection of two soft directed hypergraphs
Definition 5.1. Consider as a simple directed hypergraph with a vertex set and a set of hyperarcs . Let and represent two soft directed
hypergraphs derived from ,
with the condition that for all . Then, the
extended intersection of
and , denoted by , is defined as
, where and for all ,
and
If , then
Example 5.2. Examine a simple directed hypergraph depicted in
Figure 6, along with its
corresponding soft directed hypergraphs illustrated in Figure 7 and depicted in Figure 8. The extended
intersection of these two soft directed hypergraphs and is where . Also , , , andand, and
Here is
a soft set over and is a soft set over . Also and
are weak induced subhypergraphs of . Hence is a soft directed hypergrah of and is given in Figure 10.
Figure 10
Theorem 5.3. Let be a simple
directed hypergraph having vertex set and hyperarc set . Also let and be two soft hypergraphs of
such that for all . Then their extended intersection is also a soft
directed hypergraph of .
Proof. The extended intersection of and is given by , where and for all ,
and
That is, in , is a parameter set, is a mapping from to and is a mapping from to . Here is a soft set over and is a soft set over . When , the corresponding
dh-part of is .
This is a weak induced subhypergraph of since is a soft directed hypergraph of
. When , the corresponding
dh-part of
is . This is a weak induced subhypergraph of since is a soft directed hypergraph of
. When , the
corresponding dh-part of is where and andand. We have and each hyperarc in is a subhyperarc of for all . So is a weak induced subhypergraph of
for all . That is, is a
weak induced subhypergraph of , for all . That is,
is a soft directed hypergraph of since the following conditions
are satisfied:
is a
simple directed hypergraph,
is a
nonempty set of parameters,
is a soft set
over ,
is a soft set
over ,
is a
weak induced subhypergraph of for all .
Theorem 5.4. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
for all . Then is a soft weak induced subhypergraph of .
Proof. By Theorems 4.3 and 5.3, we have and are soft directed
hypergraphs of . Assume
that and . By the definitions of
extended union and the extended intersection of two soft directed
hypergraphs, . Therefore we have .
We divide the parameter set into three parts: (i) (ii) (iii) . We consider the three
cases one by one.
If ,
the corresponding dh-parts and of and respectively are equal to
. That is, is a weak induced
subhypergraph of , since both dh-parts are identical.
If ,
the corresponding dh-parts and of and respectively are equal to
. That is, is a weak induced
subhypergraph of , since both dh-parts are identical.
If ,
, where and andand and , where and andand. Clearly and each hyperarc present in is a subhyperarc of a
hyperarc present in .
So is a weak induced
subhypergraph of .
That is, we have
,
For all ,
is a weak induced subhypergraph of .
Hence is
a soft weak induced subhypergraph of .
6. Restricted
union of two soft directed hypergraphs
Definition 6.1. Consider as a simple directed hypergraph with a vertex set and a set of hyperarcs . Let and represent two soft directed
hypergraphs derived from
such that . Then, the restricted union of and , denoted by , is defined as
, where and for all , and andand. If , then
Example 6.2. Examine a simple directed hypergraph as illustrated
in Figure 6, along with its soft
directed hypergraphs
depicted in Figure 7 and shown in Figure 8. The restricted union of
these two soft directed hypergraphs and is where . Also
, andand Here is a soft set over and is a soft set over . Also is a weak
induced subhypergraph of .
Hence is a soft directed hypergrah of and is given in Figure 11.
Figure 11
Theorem 6.3. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
. Then
their restricted union is also a soft directed hypergraph of .
Proof. The restricted union is defined as
, where is the
parameter set and for all , and andand. Here is a mapping from to and is a mapping from to . Also is a soft set over and is a soft set over . When , the
corresponding dh-part of is where and andand. We have and each hyperarc in is a subhyperarc of for all . So is a
weak induced subhypergraph of for all . That is,
is a soft directed hypergraph of since all the conditions for a
soft directed hypergraph are satisfied.
Theorem 6.4. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
. Then
is a soft
weak induced subhypergraph of .
Proof. By Theorems 4.3 and 6.3, we have and are soft directed
hypergraphs of . Assume
that and . By the definitions of
extended union and restricted union of two soft directed hypergraphs,
the parameter set of is and the parameter set
of is . Clearly we have since . If , , where and andand and , where and andand. Clearly is a weak induced
subhypergraph of , since both dh-parts are
identical. That is, we have
,
For all ,
is a weak induced subhypergraph of .
Hence is
a soft weak induced subhypergraph of .
7. Restricted
intersection of two soft directed hypergraphs
Definition 7.1. Let be
a simple directed hypergraph having vertex set and hyperarc set . Also let and be two soft directed
hypergraphs of such that
and for all . Then the restricted intersection of and denoted by is defined as
, where and for all , and andand. If , then
Example 7.2. Take into account a simple directed hypergraph as depicted in
Figure 6, along with its soft
directed hypergraphs
presented in Figure 7 and illustrated in Figure 8, correspondingly. The
restricted intersection of these two soft directed hypergraphs and is where . Also
, andand. Here is
a soft set over and is a soft set over . Also is a weak
induced subhypergraph of .
Hence is a soft directed hypergraph of and is given in Figure 12.
Figure 12
Theorem 7.3. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
and for all . Then their restricted intersection is also a soft
directed hypergraph of .
Proof. The restricted intersection is defined as
, where is the
parameter set and for all , and andand. Here is a mapping from to and is a mapping from to . Also is a soft set over and is a soft set over . When , the
corresponding dh-part of is where and andand. We have and each hyperarc in is a subhyperarc of for all . So is a
weak induced subhypergraph of for all . That is,
is a soft directed hypergraph of since all the conditions for a
soft directed hypergraph are satisfied.
Theorem 7.4. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
and for all . Then is a soft weak induced subhypergraph of .
Proof. By Theorems 5.3 and 7.3, we have and are soft directed
hypergraphs of . Assume
that and . By the definitions of
extended intersection and restricted intersection of two soft directed
hypergraphs, the parameter set of is and the parameter set
of is . Clearly we have since . If , , where and andand and , where and andand. Clearly is a weak induced
subhypergraph of , since both dh-parts are
identical. That is, we have
,
For all ,
is a weak induced subhypergraph of .
Hence is
a soft weak induced subhypergraph of .
Theorem 7.5. Let be a simple
directed hypergraph and and be two soft directed
hypergraphs of such that
and for all . Then is a soft weak induced subhypergraph of .
Proof. By Theorems 4.3 and 7.3, we have and are soft directed
hypergraphs of . Assume
that and . By the definitions of
extended union and restricted intersection of two soft directed
hypergraphs, the parameter set of is and the parameter set
of is . Clearly we have since . If , , where and andand and , where and andand. Clearly is a weak induced
subhypergraph of . That is, we have
,
For all ,
is a weak induced subhypergraph of .
Hence is
a soft weak induced subhypergraph of .
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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