|
In mathematics, the longest element of a Coxeter group is the unique element of maximal length in a finite Coxeter group with respect to the chosen generating set consisting of simple reflections. It is often denoted by ''w''0. See and . == Properties == * A Coxeter group has a longest element if and only if it is finite; "only if" is because the size of the group is bounded by the number of words of length less than or equal to the maximum. * The longest element of a Coxeter group is the unique maximal element with respect to the Bruhat order. * The longest element is an involution (has order 2: ), by uniqueness of maximal length (the inverse of an element has the same length as the element). * For any the length satisfies 〔 * A reduced expression for the longest element is not in general unique. * In a reduced expression for the longest element, every simple reflection must occur at least once.〔 * If the Coxeter group is a finite Weyl group then the length of ''w''0 is the number of the positive roots. * The open cell ''Bw''0''B'' in the Bruhat decomposition of a semisimple algebraic group ''G'' is dense in Zariski topology; topologically, it is the top dimensional cell of the decomposition, and represents the fundamental class. * The longest element is the central element –1 except for (), for ''n'' odd, and for ''p'' odd, when it is –1 multiplied by the order 2 automorphism of the Coxeter diagram. 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「Longest element of a Coxeter group」の詳細全文を読む スポンサード リンク
|