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:''For a closed immersion in algebraic geometry, see closed immersion.'' In mathematics, an immersion is a differentiable function between differentiable manifolds whose derivative is everywhere injective.〔This definition is given by , , , , , , , .〕 Explicitly, ''f'' : ''M'' → ''N'' is an immersion if : is an injective function at every point ''p'' of ''M'' (where ''TpX'' denotes the tangent space of a manifold ''X'' at a point ''p'' in ''X''). Equivalently, ''f'' is an immersion if its derivative has constant rank equal to the dimension of ''M'':〔This definition is given by , .〕 : The function ''f'' itself need not be injective, only its derivative. A related concept is that of an embedding. A smooth embedding is an injective immersion ''f'' : ''M'' → ''N'' which is also a topological embedding, so that ''M'' is diffeomorphic to its image in ''N''. An immersion is precisely a local embedding – i.e. for any point ''x'' ∈ ''M'' there is a neighbourhood, ''U'' ⊂ ''M'', of ''x'' such that ''f'' : ''U'' → ''N'' is an embedding, and conversely a local embedding is an immersion.〔This kind of definition, based on local diffeomorphisms, is given by , .〕 For infinite dimensional manifolds, this is sometimes taken to be the definition of an immersion.〔This kind of infinite-dimensional definition is given by .〕 If ''M'' is compact, an injective immersion is an embedding, but if ''M'' is not compact then injective immersions need not be embeddings; compare to continuous bijections versus homeomorphisms. ==Regular homotopy== A regular homotopy between two immersions ''f'' and ''g'' from a manifold ''M'' to a manifold ''N'' is defined to be a differentiable function ''H'' : ''M'' × () → ''N'' such that for all ''t'' in (1 ) the function ''Ht'' : ''M'' → ''N'' defined by ''Ht''(''x'') = ''H''(''x'', ''t'') for all ''x'' ∈ ''M'' is an immersion, with ''H''0 = ''f'', ''H''1 = ''g''. A regular homotopy is thus a homotopy through immersions. 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「Immersion (mathematics)」の詳細全文を読む スポンサード リンク
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