# Symplectic manifold

(Redirected from Symplectic form)

In mathematics, a symplectic manifold is a smooth manifold M equipped with a closed, nondegenerate, 2-form ω called the symplectic form. The study of symplectic manifolds is called symplectic topology. Symplectic manifolds arise naturally in abstract formulations of classical mechanics and analytical mechanics as the cotangent bundles of manifolds, e.g. in the Hamiltonian formulation of classical mechanics, which provides one of the major motivations for the field: The set of all possible configurations of a system is modelled as a manifold, and this manifold's cotangent bundle describes the phase space of the system.

Any real-valued differentiable function H on a symplectic manifold can serve as an energy function or Hamiltonian. Associated to any Hamiltonian is a Hamiltonian vector field; the integral curves of the the Hamiltonian vector field are solutions to the Hamilton-Jacobi equations. The Hamiltonian vector field defines a flow on the symplectic manifold, called a Hamiltonian flow or symplectomorphism. By Liouville's theorem, Hamiltonian flows preserve the volume form on the phase space.

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## Linear symplectic manifold

There is a standard 'local' model, namely R2n with ωi,n+i = 1; ωn+i,i = -1; ωj,k = 0 for all i = 0,...,n-1; j,k=0,...,2n-1 (kj+n or jk+n). This is an example of a linear symplectic space. See symplectic vector space. A proposition known as Darboux's theorem says that locally any symplectic manifold resembles this simple one.

## Volume form

Directly from the definition, one can show that every symplectic manifold M is of even dimension 2n; this follows because ωn is a nowhere vanishing form, the symplectic volume form. It follows that every symplectic manifold is canonically oriented and comes with a canonical measure, the Liouville measure.

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