GfsPhysicalParams
From Gerris
Use GfsPhysicalParams to set the gravitational field strength g (a number) and the specific volume (the reciprocal of density) alpha (a scalar field).
For example, from the Geostrophic adjustment test case
PhysicalParams { g = 9.4534734306584e-4 }
and from the Rayleigh--Taylor example
VariableTracerVOF {} T
InitFraction {} T (0.05*cos (2.*M_PI*x) + y) { ty = 0.5 }
PhysicalParams { alpha = 1./(T*1.225 + (1. - T)*0.1694) }
(here the fluid with characteristic function T has density 1.225 and the other fluid has density 0.1694).

