A formula that expresses the connection between the flow of a vector field through a two-dimensional oriented manifold and the circulation of this field along the correspondingly oriented boundary of this manifold. Let be an oriented piecewise-smooth surface, let be the unit normal to (at those points, of course, where it exists), which defines the orientation of , and let the boundary of consist of a finite number of piecewise-smooth contours. The boundary of is denoted by , and is oriented by means of the unit tangent vector , such that the orientation of obtained is compatible with the orientation of .
If is a continuously-differentiable vector field in a neighbourhood of , then
( is the area element of , is the differential of the arc length of the boundary of ) or, in coordinate form,
Stated by G. Stokes (1854).
Stokes' formula is also the name given to a generalization of formula , which represents the equality between the integral of the exterior differential of a differential form over an oriented compact manifold and the integral of the form itself along the boundary of (the orientation of is taken to be compatible with that of ):
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Stokes formula. Encyclopedia of Mathematics. URL: http://www.encyclopediaofmath.org/index.php?title=Stokes_formula&oldid=28270