Mean curvature
= Mean curvature
{title2=$H$}
{wiki}
The mean curvature vector of an $n$-dimensional embedded submanifold is the trace $\mathbf H=\sum_iA(e_i,e_i)$. For a surface in $\mathbb R^3$, the scalar mean curvature is half the trace of the shape operator:
$$
H=\frac{eG-2fF+gE}{2(EG-F^2)}.
$$