Almost Complex Manifold

In mathematics, an almost complex manifold is a smooth manifold equipped with smooth linear complex structure on each tangent space. The existence of this structure is a necessary, but not sufficient, condition for a manifold to be a complex manifold. That is, every complex manifold is an almost complex manifold, but not vice-versa. Almost complex structures have important applications in symplectic geometry.

The concept is due to Ehresmann and Hopf in the 1940s.

Read more about Almost Complex Manifold:  Formal Definition, Examples, Differential Topology of Almost Complex Manifolds, Integrable Almost Complex Structures, Compatible Triples, Generalized Almost Complex Structure

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