# Compute solution u^n+1, use bcs u_D^n+1, u^n and coupling bcs
solve(a == L, u_np1, bcs)
# Write data to preCICE according to which problem is being solved
if problem is ProblemType.DIRICHLET:
# Dirichlet problem reads temperature and writes flux on boundary to Neumann problem
determine_gradient(V_g, u_np1, flux)
precice.write_data(flux)
elif problem is ProblemType.NEUMANN:
# Neumann problem reads flux and writes temperature on boundary to Dirichlet problem
precice.write_data(u_np1)
precice_dt = precice.advance(dt(0))
if precice.is_action_required(precice.action_read_iteration_checkpoint()): # roll back to checkpoint
u_cp, t_cp, n_cp = precice.retrieve_checkpoint()
u_n.assign(u_cp)
t = t_cp
n = n_cp
else: # update solution
u_n.assign(u_np1)
t += float(dt)
n += 1
if precice.is_time_window_complete():
u_ref = interpolate(u_D, V)
u_ref.rename("reference", " ")
error, error_pointwise = compute_errors(u_n, u_ref, V, total_error_tol=error_tol)
print('n = %d, t = %.2f: L2 error on domain = %.3g' % (n, t, error))
# output solution and reference solution at t_n+1
# Update the coupling expression with the new read data
precice.update_coupling_expression(coupling_expression, read_data)
dt.assign(np.min([fenics_dt, precice_dt]))
# Compute solution
solve(a == L, u_np1, bcs)
# Dirichlet problem obtains flux from solution and sends flux on boundary to Neumann problem
determine_heat_flux(V_g, u_np1, k, fluxes)
fluxes_y = fluxes.sub(1) # only exchange y component of flux.
precice.write_data(fluxes_y)
precice_dt = precice.advance(dt(0))
if precice.is_action_required(precice.action_read_iteration_checkpoint()
): # roll back to checkpoint
u_cp, t_cp, n_cp = precice.retrieve_checkpoint()
u_n.assign(u_cp)
t = t_cp
n = n_cp
else: # update solution
u_n.assign(u_np1)
t += float(dt)
n += 1
if precice.is_time_window_complete():
tol = 10e-5 # we need some tolerance, since otherwise output might be skipped.
if abs((t + tol) %
dt_out) < 2 * tol: # output if t is a multiple of dt_out
print("output vtk for time = {}".format(float(t)))