Mean curvature

of a surface in -dimensional Euclidean space Half of the sum of the principal curvatures (cf. Principal curvature) and , calculated at a point of this surface: For a hypersurface in the Euclidean space , this formula is generalized in the following way: where , , are the principal curvatures of the hypersurface, calculated at a point .

The mean curvature of a surface in can be expressed by means of the coefficients of the first and second fundamental forms of this surface: where are the coefficients of the first fundamental form, and are the coefficients of the second fundamental form, calculated at a point . In the particular case where the surface is defined by an equation , the mean curvature is calculated using the formula:  which is generalized for a hypersurface in , defined by the equation , as follows: where For an -dimensional submanifold of an -dimensional Euclidean space of codimension , the mean curvature generalizes to the notion of the mean curvature normal where is an orthonormal frame of the normal space (cf. Normal space (to a surface)) of at and ( denotes the tangent space to at ) is the shape operator of at in the direction , which is related to the second fundamental tensor of at by .