Knight's graph
In graph theory, a knight's graph, or a knight's tour graph, is a graph that represents all legal moves of the knight chess piece on a chessboard. Each vertex of this graph represents a square of the chessboard, and each edge connects two squares that are a knight's move apart from each other.
More specifically, an knight's graph is a knight's graph of an chessboard.
Its vertices can be represented as the points of the Euclidean plane whose Cartesian coordinates are integers with and , and with two
vertices connected by an edge when their Euclidean distance is.
For an knight's graph, the number of vertices is. For an knight's graph, the number of vertices is and the number of edges is.
A Hamiltonian cycle on the knight's graph is a knight's tour. A chessboard with an odd number of squares has no tour, because the knight's graph is a bipartite graph and only the bipartite graphs with an even number of vertices can have Hamiltonian cycles. All but finitely many chessboards with an even number of squares have a knight's tour; Schwenk's theorem provides an exact listing of which ones do and which do not.
When it is modified to have toroidal boundary conditions the knight's graph is the same as the four-dimensional hypercube graph.
