Hypergraph

In mathematics, a hypergraph is a generalization of a graph in which an edge can join any number of vertices. Formally, a hypergraph H {displaystyle H} is a pair H = ( X , E ) {displaystyle H=(X,E)} where X {displaystyle X} is a set of elements called nodes or vertices, and E {displaystyle E} is a set of non-empty subsets of X {displaystyle X} called hyperedges or edges. Therefore, E {displaystyle E} is a subset of P ( X ) ∖ { ∅ } {displaystyle {mathcal {P}}(X)setminus {emptyset }} , where P ( X ) {displaystyle {mathcal {P}}(X)} is the power set of X {displaystyle X} . The size of vertex set is called the order of the hypergraph, and the size of edges set is the size of the hypergraph. In mathematics, a hypergraph is a generalization of a graph in which an edge can join any number of vertices. Formally, a hypergraph H {displaystyle H} is a pair H = ( X , E ) {displaystyle H=(X,E)} where X {displaystyle X} is a set of elements called nodes or vertices, and E {displaystyle E} is a set of non-empty subsets of X {displaystyle X} called hyperedges or edges. Therefore, E {displaystyle E} is a subset of P ( X ) ∖ { ∅ } {displaystyle {mathcal {P}}(X)setminus {emptyset }} , where P ( X ) {displaystyle {mathcal {P}}(X)} is the power set of X {displaystyle X} . The size of vertex set is called the order of the hypergraph, and the size of edges set is the size of the hypergraph. While graph edges are 2-element subsets of nodes, hyperedges are arbitrary sets of nodes, and can therefore contain an arbitrary number of nodes. However, it is often desirable to study hypergraphs where all hyperedges have the same cardinality; a k-uniform hypergraph is a hypergraph such that all its hyperedges have size k. (In other words, one such hypergraph is a collection of sets, each such set a hyperedge connecting k nodes.) So a 2-uniform hypergraph is a graph, a 3-uniform hypergraph is a collection of unordered triples, and so on. A hypergraph is also called a set system or a family of sets drawn from the universal set. Hypergraphs can be viewed as incidence structures. In particular, there is a bipartite 'incidence graph' or 'Levi graph' corresponding to every hypergraph, and conversely, most, but not all, bipartite graphs can be regarded as incidence graphs of hypergraphs. Hypergraphs have many other names. In computational geometry, a hypergraph may sometimes be called a range space and then the hyperedges are called ranges.In cooperative game theory, hypergraphs are called simple games (voting games); this notion is applied to solve problems in social choice theory. In some literature edges are referred to as hyperlinks or connectors. Special kinds of hypergraphs include: k-uniform ones, as discussed briefly above; clutters, where no edge appears as a subset of another edge; and abstract simplicial complexes, which contain all subsets of every edge. The collection of hypergraphs is a category with hypergraph homomorphisms as morphisms. There are different types of hypergraphs such as: Because hypergraph links can have any cardinality, there are several notions of the concept of a subgraph, called subhypergraphs, partial hypergraphs and section hypergraphs. Let H = ( X , E ) {displaystyle H=(X,E)} be the hypergraph consisting of vertices