def error_norm(self, N, n_mg):
"Return the infinity norm of errors for the u component."
geometry, enthalpy, yield_stress = self.inputs(N)
# set the number of multigrid levels
self.opt.setValue("-bp_pc_mg_levels", n_mg)
grid = enthalpy.grid()
blatter_Mz = N
coarsening_factor = 4
model = PISM.BlatterTestXZ(grid, blatter_Mz, coarsening_factor)
model.init()
inputs = PISM.StressBalanceInputs()
inputs.geometry = geometry
inputs.basal_yield_stress = yield_stress
inputs.enthalpy = enthalpy
# run the solver
model.update(inputs, True)
u_model_z = model.velocity_u_sigma().levels()
u_model = PISM.IceModelVec3(grid, "u_model", PISM.WITHOUT_GHOSTS,
u_model_z)
u_model.set_attrs("model", "modeled velocity", "m / s", "m / year", "",
0)
u_model.copy_from(model.velocity_u_sigma())
u_exact = self.exact_solution(grid, geometry.bed_elevation, u_model_z)
# compute the error
u_error = PISM.IceModelVec3(grid, "error", PISM.WITHOUT_GHOSTS,
u_model_z)
u_error.copy_from(u_exact)
u_error.add(-1.0, model.velocity_u_sigma())
return u_error.norm(PISM.PETSc.NormType.NORM_INFINITY)[0]
