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In mathematics, a quiver is a directed graph where loops and multiple arrows between two vertices are allowed, i.e. a multidigraph. They are commonly used in representation theory: a representation ''V'' of a quiver assigns a vector space ''V''(''x'') to each vertex ''x'' of the quiver and a linear map ''V''(''a'') to each arrow ''a''. In category theory, a quiver can be understood to be an underlying structure of a category, but without identity morphisms and composition. That is, there is a forgetful functor from Cat to Quiv. Its left adjoint is a free functor which, from a quiver, makes the corresponding free category. ==Definition== A quiver Γ consists of: * The set ''V'' of vertices of Γ * The set ''E'' of edges of Γ * Two functions: ''s'': ''E'' → ''V'' giving the ''start'' or ''source'' of the edge, and another function, ''t'': ''E'' → ''V'' giving the ''target'' of the edge. This definition is identical to that of a multidigraph. A morphism of quivers is defined as follows. If and are two quivers, then a morphism of quivers consist of two functions and such that following diagrams commute: : and : 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「Quiver (mathematics)」の詳細全文を読む スポンサード リンク
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