def error_norm(self, N):
"Return the infinity norm of errors for the u and v components (as a tuple)."
geometry, enthalpy, yield_stress = self.inputs(N)
grid = enthalpy.grid()
u_exact = self.exact_solution(grid)
# no variation in the Z direction, so it's OK to use 2 vertical levels
blatter_Mz = 2
coarsening_factor = 1
model = PISM.BlatterTestXY(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)
# compute the error
error = PISM.IceModelVec2V(grid, "error", PISM.WITHOUT_GHOSTS)
error.copy_from(u_exact)
error.add(-1.0, model.velocity())
return error.norm(PISM.PETSc.NormType.NORM_INFINITY)
