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In mathematics, Lie algebroids serve the same role in the theory of Lie groupoids that Lie algebras serve in the theory of Lie groups: reducing global problems to infinitesimal ones. Just as a Lie groupoid can be thought of as a "Lie group with many objects", a Lie algebroid is like a "Lie algebra with many objects". More precisely, a Lie algebroid is a triple consisting of a vector bundle over a manifold , together with a Lie bracket on its module of sections and a morphism of vector bundles called the anchor. Here is the tangent bundle of . The anchor and the bracket are to satisfy the Leibniz rule: : where and is the derivative of along the vector field . It follows that : for all . == Examples == * Every Lie algebra is a Lie algebroid over the one point manifold. * The tangent bundle of a manifold is a Lie algebroid for the Lie bracket of vector fields and the identity of as an anchor. * Every integrable subbundle of the tangent bundle — that is, one whose sections are closed under the Lie bracket — also defines a Lie algebroid. * Every bundle of Lie algebras over a smooth manifold defines a Lie algebroid where the Lie bracket is defined pointwise and the anchor map is equal to zero. * To every Lie groupoid is associated a Lie algebroid, generalizing how a Lie algebra is associated to a Lie group (see also below). For example, the Lie algebroid comes from the pair groupoid whose objects are , with one isomorphism between each pair of objects. Unfortunately, going back from a Lie algebroid to a Lie groupoid is not always possible,〔Marius Crainic, Rui L. Fernandes. (Integrability of Lie brackets ), Ann. of Math. (2), Vol. 157 (2003), no. 2, 575--620〕 but every Lie algebroid gives a stacky Lie groupoid.〔Hsian-Hua Tseng and Chenchang Zhu, Integrating Lie algebroids via stacks, Compositio Mathematica, Volume 142 (2006), Issue 01, pp 251-270, available as (arXiv:math/0405003 )〕〔Chenchang Zhu, Lie II theorem for Lie algebroids via stacky Lie groupoids, available as (arXiv:math/0701024 )〕 * Given the action of a Lie algebra g on a manifold M, the set of g -invariant vector fields on M is a Lie algebroid over the space of orbits of the action. * The Atiyah algebroid of a principal ''G''-bundle ''P'' over a manifold ''M'' is a Lie algebroid with short exact sequence: *: : The space of sections of the Atiyah algebroid is the Lie algebra of ''G''-invariant vector fields on ''P''. 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「Lie algebroid」の詳細全文を読む スポンサード リンク
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