Discrete exterior calculus
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(February 2009)

In mathematics, the discrete exterior calculus (DEC) is the extension of the exterior calculus to discrete spaces including graphs and finite element meshes. DEC methods have proved to be very powerful in improving and analyzing finite element methods: for instance, DECbased methods allow the use of highly nonuniform meshes to obtain accurate results. Nonuniform meshes are advantageous because they allow the use of large elements where the process to be simulated is relatively simple, as opposed to a fine resolution where the process may be complicated (e.g., near an obstruction to a fluid flow), while using less computational power than if a uniformly fine mesh were used.
The discrete exterior derivative
Stokes' theorem relates the integral of a differential (n − 1)form ω over the boundary ∂M of an ndimensional manifold M to the integral of dω (the exterior derivative of ω, and a differential nform on M) over M itself:
One could think of differential kforms as linear operators that act on kdimensional "bits" of space, in which case one might prefer to use the bra–ket notation for a dual pairing. In this notation, Stokes' theorem reads as
In finite element analysis, the first stage is often the approximation of the domain of interest by a triangulation, T. For example, a curve would be approximated as a union of straight line segments; a surface would be approximated by a union of triangles, whose edges are straight line segments, which themselves terminate in points. Topologists would refer to such a construction as a simplicial complex. The boundary operator on this triangulation/simplicial complex T is defined in the usual way: for example, if L is a directed line segment from one point, a, to another, b, then the boundary ∂L of L is the formal difference b − a.
A kform on T is a linear operator acting on kdimensional subcomplexes of T; e.g., a 0form assigns values to points, and extends linearly to linear combinations of points; a 1form assigns values to line segments in a similarly linear way. If S is a (k + 1)dimensional subcomplex of T and ω is a kform on T, then the discrete exterior derivative dω of ω is the unique (k + 1)form defined so that Stokes' theorem holds:
Other concepts such as the discrete wedge product and the discrete Hodge star can also be defined.
See also
References
 Discrete Calculus, Grady, Leo J., Polimeni, Jonathan R., ISBN 9781849962896, 2010
 Discrete Exterior Calculus with Convergence to the Smooth Continuum
 Hirani Thesis on Discrete Exterior Calculus
 On geometric discretization of elasticity, Arash Yavari, J. Math. Phys. 49, 022901 (2008), DOI:10.1063/1.2830977