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In mathematical group theory, the root datum of a connected split reductive algebraic group over a field is a generalization of a root system that determines the group up to isomorphism. They were introduced by Michel Demazure in SGA III, published in 1970. ==Definition== A root datum consists of a quadruple :, where * and are free abelian groups of finite rank together with a perfect pairing between them with values in which we denote by ( , ) (in other words, each is identified with the dual lattice of the other). * is a finite subset of and is a finite subset of and there is a bijection from onto , denoted by . * For each , . * For each , the map induces an automorphism of the root datum (in other words it maps to and the induced action on maps to ) The elements of are called the roots of the root datum, and the elements of are called the coroots. The elements of are sometimes called weights and those of accordingly coweights. If does not contain for any , then the root datum is called reduced. 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「root datum」の詳細全文を読む スポンサード リンク
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