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In mathematics, an Igusa group or Igusa subgroup is a subgroup of the Siegel modular group defined by some congruence conditions. They were introduced by . ==Definition== The symplectic group Sp2''g''(Z) consists of the matrices : such that ''ABt'' and ''CDt'' are symmetric, and ''ADt − ''CDt'' = ''I'' (the identity matrix). The Igusa group Γg(''n'',2''n'') = Γ''n'',2''n'' consists of the matrices : in Sp2''g''(Z) such that ''B'' and ''C'' are congruent to 0 mod ''n'', ''A'' and ''D'' are congruent to the identity matrix ''I'' mod ''n'', and the diagonals of ''ABt'' and ''CDt'' are congruent to 0 mod 2''n''. We have Γg(2''n'')⊆ Γg(''n'',2''n'') ⊆ Γg(''n'') where Γg(''n'') is the subgroup of matrices congruent to the identity modulo ''n''. 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「Igusa group」の詳細全文を読む スポンサード リンク
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