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In contexts including complex manifolds and algebraic geometry, a logarithmic differential form is a meromorphic differential form with poles of a certain kind. Let ''X'' be a complex manifold, and ''D'' ⊂ ''X'' a divisor and ω a holomorphic ''p''-form on ''X''−''D''. If ω and ''d''ω have a pole of order at most one along ''D'', then ω is said to have a logarithmic pole along ''D''. ω is also known as a logarithmic ''p''-form. The logarithmic ''p''-forms make up a subsheaf of the meromorphic ''p''-forms on ''X'' with a pole along ''D'', denoted : In the theory of Riemann surfaces, one encounters logarithmic one-forms which have the local expression : for some meromorphic function (resp. rational function) , where ''g'' is holomorphic and non-vanishing at 0, and ''m'' is the order of ''f'' at ''0''. That is, for some open covering, there are local representations of this differential form as a logarithmic derivative (modified slightly with the exterior derivative ''d'' in place of the usual differential operator ''d/dz''). Observe that ω has only simple poles with integer residues. On higher-dimensional complex manifolds, the Poincaré residue is used to describe the distinctive behavior of logarithmic forms along poles. ==Holomorphic log complex== By definition of and the fact that exterior differentiation ''d'' satisfies ''d''2 = 0, one has :. This implies that there is a complex of sheaves , known as the ''holomorphic log complex'' corresponding to the divisor ''D''. This is a subcomplex of , where is the inclusion and is the complex of sheaves of holomorphic forms on ''X''−''D''. Of special interest is the case where ''D'' has simple normal crossings. Then if are the smooth, irreducible components of ''D'', one has with the meeting transversely. Locally ''D'' is the union of hyperplanes, with local defining equations of the form in some holomorphic coordinates. One can show that the stalk of at ''p'' satisfies〔Chris A.M. Peters; Joseph H.M. Steenbrink (2007). Mixed Hodge Structures. Springer. ISBN 978-3-540-77017-6〕 : and that :. Some authors, e.g.,〔Phillip A. Griffiths; Joseph Harris (1979). Principles of Algebraic Geometry. Wiley-Interscience. ISBN 0-471-05059-8.〕 use the term ''log complex'' to refer to the holomorphic log complex corresponding to a divisor with normal crossings. 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「logarithmic form」の詳細全文を読む スポンサード リンク
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