accumulation_impl adjust_mass_flux define_model_state_impl ForceThickness init_impl m_alpha m_alpha_ice_free_factor m_ftt_mask m_ice_free_thickness_threshold m_mass_flux m_start_time m_target_thickness mass_flux_impl max_timestep_impl melt_impl runoff_impl update_impl write_model_state_impl ~ForceThickness

max_timestep_impl() MaxTimestep pism::surface::ForceThickness::max_timestep_impl ( double  my_t ) const protectedvirtual The timestep restriction is, by direct analogy, the same as for $$\frac{dy}{dt} = - \alpha y$$ with explicit (forward) Euler. If $\Delta t$ is the time step then Euler is $y_{n+1} = (1-\alpha \Delta t) y_n$. We require for stability that $|y_{n+1}|\le |y_n|$, which is to say $|1-\alpha \Delta t|\le 1$. Equivalently (since $\alpha \Delta t>0$), $$\alpha \Delta t\le 2$$ Therefore we set here $$\Delta t = \frac{2}{\alpha}.$$ Reimplemented from pism::surface::SurfaceModel. Definition at line 292 of file ForceThickness.cc. References m_alpha, and pism::surface::SurfaceModel::m_input_model.