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In graph theory, the graph removal lemma states that when a graph contains few copies of a given subgraph, then all of the copies can be eliminated by removing a small number of edges. [1] The special case in which the subgraph is a triangle is known as the triangle removal lemma .
A balanced tripartite graph with the unique triangle property can be made into a partitioned bipartite graph by removing one of its three subsets of vertices, and making an induced matching on the neighbors of each removed vertex. To convert a graph with a unique triangle per edge into a triple system, let the triples be the triangles of the graph.
When modelling relations between two different classes of objects, bipartite graphs very often arise naturally. For instance, a graph of football players and clubs, with an edge between a player and a club if the player has played for that club, is a natural example of an affiliation network, a type of bipartite graph used in social network analysis.
In graph theory, a split of an undirected graph is a cut whose cut-set forms a complete bipartite graph.A graph is prime if it has no splits. The splits of a graph can be collected into a tree-like structure called the split decomposition or join decomposition, which can be constructed in linear time.
For bipartite graphs, the Erdős–Stone theorem only tells us that (,) = (). The forbidden subgraph problem for bipartite graphs is known as the Zarankiewicz problem, and it is unsolved in general. Progress on the Zarankiewicz problem includes following theorem:
Any regular bipartite graph. [1] Hall's marriage theorem can be used to show that a k-regular bipartite graph contains a perfect matching. One can then remove the perfect matching to obtain a (k − 1)-regular bipartite graph, and apply the same reasoning repeatedly. Any complete graph with an even number of nodes (see below). [2]
Let G be a bipartite graph, M a maximum-cardinality matching in G, and V 0 the set of vertices of G unmatched by M (the "free vertices"). Then G can be partitioned into three parts: The E-O-U decomposition. E - the even vertices - the vertices reachable from V 0 by an M-alternating path of even length.
Alternatively, describing the problem using graph theory: The assignment problem consists of finding, in a weighted bipartite graph, a matching of a given size, in which the sum of weights of the edges is minimum. If the numbers of agents and tasks are equal, then the problem is called balanced assignment.