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monodromy
In mathematics, monodromy is the study of how objects from mathematical analysis, algebraic topology, algebraic geometry and differential geometry behave as they 'run round' a singularity. As the name implies, the fundamental meaning of ''monodromy'' comes from 'running round singly'. It is closely associated with covering maps and their degeneration into ramification; the aspect giving rise to monodromy phenomena is that certain functions we may wish to define fail to be ''single-valued'' as we 'run round' a path encircling a singularity. The failure of monodromy is best measured by defining a monodromy group: a group of transformations acting on the data that encodes what does happen as we 'run round'. ==Definition== Let ''X'' be a connected and locally connected based topological space with base point ''x'', and let be a covering with fiber . For a loop based at ''x'', denote a lift under the covering map (starting at a point ) by . Finally, we denote by the endpoint , which is generally different from . There are theorems which state that this construction gives a well-defined group action of the fundamental group π1(''X'', ''x'') on ''F'', and that the stabilizer of is exactly , that is, an element () fixes a point in ''F'' if and only if it is represented by the image of a loop in based at . This action is called the monodromy action and the corresponding homomorphism π1(''X'', ''x'') → Aut(''H'' *(''Fx'')) into the automorphism group on ''F'' is the algebraic monodromy. The image of this homomorphism is the monodromy group. There is another map π1(''X'', ''x'') → Diff(''Fx'')/Is(''Fx'') whose image is called the geometric monodromy group.
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「monodromy」の詳細全文を読む
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