An abstract type representing the initial conditions and the boundary conditions for a
P should define the methods below.
init_state_prognostic!( ::P, ::BalanceLaw, state_prognostic::Vars, state_auxiliary::Vars, localgeo, t, args..., )
Initialize the prognostic state variables at $t = 0$.
init_state_auxiliary!( ::P, ::BalanceLaw, state_auxiliary::Vars, geom::LocalGeometry, )
Initialize the auxiliary state, at $t = 0$.