f := gp.mass.inertial(gp)

Get the gridpoint inertial mass.

The inertial mass is calculated during the equations-of-motion calculation for a gridpoint. In static (default) mode, it is calculated from the accumulated gridpoint stiffness, as described in Mechanical Timestep Determination for Numerical Stability. In dynamic mode, it is assigned the value of the gravitational mass. To adjust the inertial mass, see the gp.mass.add intrinsic.

Returns:f - the inertial mass of the gridpoint
Arguments:gp - a zone gridpoint pointer

[DR: please confirm link to mechtimestepdetermination above is going where wanted]