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In mathematics, the signature operator is an elliptic differential operator defined on a certain subspace of the space of differential forms on an even-dimensional compact Riemannian manifold, whose analytic index is the same as the topological signature of the manifold if the dimension of the manifold is a multiple of four. It is an instance of a Dirac-type operator. ==Definition in the even-dimensional case== Let be a compact Riemannian manifold of even dimension . Let : be the exterior derivative on -th order differential forms on . The Riemannian metric on allows us to define the Hodge star operator and with it the inner product : on forms. Denote by : the adjoint operator of the exterior differential . This operator can be expressed purely in terms of the Hodge star operator as follows: : Now consider acting on the space of all forms . One way to consider this as a graded operator is the following: Let be an involution on the space of ''all'' forms defined by: : It is verified that anti-commutes with and, consequently, switches the -eigenspaces of Consequently, : Definition: The operator with the above grading respectively the above operator is called the signature operator 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「Signature operator」の詳細全文を読む スポンサード リンク
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