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In mathematics, the Iwasawa decomposition KAN of a semisimple Lie group generalises the way a square real matrix can be written as a product of an orthogonal matrix and an upper triangular matrix (a consequence of Gram–Schmidt orthogonalization). It is named after Kenkichi Iwasawa, the Japanese mathematician who developed this method. ==Definition== *''G'' is a connected semisimple real Lie group. * is the Lie algebra of ''G'' * is the complexification of . *θ is a Cartan involution of * is the corresponding Cartan decomposition * is a maximal abelian subalgebra of *Σ is the set of restricted roots of , corresponding to eigenvalues of acting on . *Σ+ is a choice of positive roots of Σ * is a nilpotent Lie algebra given as the sum of the root spaces of Σ+ *''K'', ''A'', ''N'', are the Lie subgroups of ''G'' generated by and . Then the Iwasawa decomposition of is : and the Iwasawa decomposition of ''G'' is : The dimension of ''A'' (or equivalently of ) is called the real rank of ''G''. Iwasawa decompositions also hold for some disconnected semisimple groups ''G'', where ''K'' becomes a (disconnected) maximal compact subgroup provided the center of ''G'' is finite. The restricted root space decomposition is : where is the centralizer of in and is the root space. The number is called the multiplicity of . 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「Iwasawa decomposition」の詳細全文を読む スポンサード リンク
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