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In graph theory, a book graph (often written ) may be any of several kinds of graph. One kind, which may be called a quadrilateral book, consists of ''p'' quadrilaterals sharing a common edge (known as the "spine" or "base" of the book).〔(Eric W. Weisstein, "Book Graph." ) From MathWorld–A Wolfram Web Resource.〕 A book of this type is the Cartesian product of a star and ''K''2 . A second type, which might be called a triangular book, is the complete tripartite graph ''K''1,1,''p''. It is a graph consisting of triangles sharing a common edge.〔Lingsheng Shi and Zhipeng Song, Upper bounds on the spectral radius of book-free and/or ''K''2,l-free graphs. ''Linear Algebra and its Applications'', vol. 420 (2007), pp. 526–529. 〕 A book of this type is a split graph. This graph has also been called a . Given a graph , one may write for the largest book (of the kind being considered) contained within . The term "book-graph" has been employed for other uses. Barioli〔Francesco Barioli, Completely positive matrices with a book-graph. ''Linear Algebra and its Applications'', vol. 277 (1998), pp. 11–31. 〕 used it to mean a graph composed of a number of arbitrary subgraphs having two vertices in common. (Barioli did not write for his book-graph.) ==Theorems on books== Denote the Ramsey number of two (triangular) books by * If , then (proved by Rousseau and Sheehan). * There exists a constant such that whenever . * If , and is large, the Ramsey number is given by . * Let be a constant, and . Then every graph on vertices and edges contains a (triangular) .〔P. Erdos, (On a theorem of Rademacher-Turán ). ''Illinois Journal of Mathematics'', vol. 6 (1962), pp. 122–127.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Book (graph theory)」の詳細全文を読む スポンサード リンク
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