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・ Signature crime
・ Signature defect
・ Signature dish
・ Signature Drinks
・ Signature file
・ Signature forgery
・ Signature Half-Step a Retrospective 2000-2014
・ Signature in the Cell
・ Signature island
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・ Signature mark
・ Signature matrix
・ Signature move
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・ Signature of Divine (Yahweh)
Signature operator
・ Signature Place
・ Signature program
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・ Signature Record Type Definition
・ Signature Records
・ Signature School
・ Signature Select
・ Signature song
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・ Signature Sounds Recordings
・ Signature tag
・ Signature Team
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・ Signature Theatre (Arlington, Virginia)


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Signature operator : ウィキペディア英語版
Signature operator
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 M be a compact Riemannian manifold of even dimension 2l. Let
: d : \Omega^p(M)\rightarrow \Omega^(M)
be the exterior derivative on i-th order differential forms on M. The Riemannian metric on M allows us to define the Hodge star operator \star and with it the inner product
:\langle\omega,\eta\rangle=\int_M\omega\wedge\star\eta
on forms. Denote by
: d^
*: \Omega^(M)\rightarrow \Omega^p(M)
the adjoint operator of the exterior differential d. This operator can be expressed purely in terms of the Hodge star operator as follows:
:d^
*= (-1)^ \star d \star= - \star d \star
Now consider d + d^
* acting on the space of all forms \Omega(M)=\bigoplus_^\Omega^(M).
One way to consider this as a graded operator is the following: Let \tau be an involution on the space of ''all'' forms defined by:
: \tau(\omega)=i^\star \omega\quad,\quad\omega \in \Omega^p(M)
It is verified that d + d^
* anti-commutes with \tau and, consequently, switches the (\pm 1) -eigenspaces \Omega_(M) of \tau
Consequently,
: d + d^
* = \begin 0 & D \\ D^
* & 0 \end
Definition: The operator d + d^
* with the above grading respectively the above operator D: \Omega_+(M) \rightarrow \Omega_-(M) is called the signature operator of M.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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