SV is the second spatial derivative of height.

In the classical (slow-moving) limit it is possible to ignore the time compared with spatial derivatives so that the last equation reduces to.

A gravity gradient is simply the spatial derivative of the gravity vector.

Ordinary differential equations - continuous time, continuous state space, no spatial derivatives.

Partial differential equations - continuous time, continuous state space, spatial derivatives.

When a function also depends on a parameter such as time, the gradient often refers simply to the vector of its spatial derivatives only.

Such voids can cause computational problems, e.g. when calculating spatial derivatives of various quantities.

Note that the corrector step uses backward finite difference approximations for spatial derivative.

Changes in intensity thus relate to the first spatial derivative of the refractive index.

The spatial derivatives can then be approximated by two first order and a second order central finite differences.