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In mathematics, differential forms provide a unified approach to define integrands over curves, surfaces, solids, and higher-dimensional manifolds. The modern notion of differential forms was pioneered by Élie Cartan. It has many applications, especially in geometry, topology and physics.
In mathematics, especially vector calculus and differential topology, a closed form is a differential form α whose exterior derivative is zero (dα = 0), and an exact form is a differential form, α, that is the exterior derivative of another differential form β. Thus, an exact form is in the image of d, and a closed form is in the kernel of d.
The exterior derivative is a notion of differentiation of differential forms which generalizes the differential of a function (which is a differential 1-form). Pullback is, in particular, a geometric name for the chain rule for composing a map between manifolds with a differential form on the target manifold.
The most basic non-trivial differential one-form is the "change in angle" form . This is defined as the derivative of the angle "function" θ ( x , y ) {\\displaystyle \\theta (x,y)} (which is only defined up to an additive constant), which can be explicitly defined in terms of the atan2 function.
The wedge product of complex differential forms is defined in the same way as with real forms. Let p and q be a pair of non-negative integers ≤ n. The space Ω p,q of (p, q)-forms is defined by taking linear combinations of the wedge products of p elements from Ω 1,0 and q elements from Ω 0,1. Symbolically,
In multivariate calculus, a differential or differential form is said to be exact or perfect (exact differential), as contrasted with an inexact differential, if it is equal to the general differential for some differentiable function in an orthogonal coordinate system (hence is a multivariable function whose variables are independent, as they are always expected to be when treated in ...
Explicitly, a differential graded algebra is a graded associative algebra with a chain complex structure that is compatible with the algebra structure. In geometry, the de Rham algebra of differential forms on a manifold has the structure of a differential graded algebra, and it encodes the de Rham cohomology of the manifold.
More generally, any covariant tensor field – in particular any differential form – on may be pulled back to using . When the map ϕ {\displaystyle \phi } is a diffeomorphism , then the pullback, together with the pushforward , can be used to transform any tensor field from N {\displaystyle N} to M {\displaystyle M} or vice versa.