 ```python
import argparse
import sys
import numpy as np
import matplotlib.pyplot as plt
from scipy.sparse.linalg import spsolve
from mumps import *
import fealpy.functionspace as fncs
import fealpy.timeintegrator as timeint
import fealpy.timehistory as th
import fealpy.tool as tool
import navier_stokes_mold_2d as ns

parser = argparse.ArgumentParser()
parser.add_argument('--degree_u', type=int, default=2, help='degree of motion finite element space')
parser.add_argument('--degree_p', type=int, default=1, help='degree of pressure finite element space')
parser.add_argument('--time_divisions', type=int, default=100, help='number of time divisions')
parser.add_argument('--end_time', type=float, default=1.0, help='evolution end time')
parser.add_argument('--output_dir', type=str, default='./output', help='output directory')
parser.add_argument('--steps', type=int, default=10, help='number of time steps to output')
parser.add_argument('--nonlinear_method', type=str, default='explicit', help='non-linearization method')
args = parser.parse_args()

degree_u = args.degree_u
degree_p = args.degree_p
time_divisions = args.time_divisions
end_time = args.end_time
output_dir = args.output_dir
steps = args.steps
nonlinear_method = args.nonlinear_method

mesh = fncs.TriangleMesh.unit_square()
time_line = timeint.UniformTimeLine(0, end_time, time_divisions)

U = fncs.LagrangeFiniteElementSpace(mesh, ('DQ', degree_u))
P = fncs.LagrangeFiniteElementSpace(mesh, ('DQ', degree_p))

ndof_u = U.number_of_global_dofs()
ndof_p = P.number_of_global_dofs()

fes = U + P

bilinear_form = fncs.BilinearForm(fes)
bilinear_form += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space())
bilinear_form += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space(), form='dual')
bilinear_form += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space())
bilinear_form += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space(), form='dual')
bilinear_form += fncs.PressureIntegrator(ns.pressure, u=P.extract_sub_space())

mixed_bilinear_form = fncs.MixedBilinearForm(fes)
mixed_bilinear_form += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space(), v=U.extract_sub_space())
mixed_bilinear_form += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space(), v=U.extract_sub_space(), form='dual')
mixed_bilinear_form += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space(), v=U.extract_sub_space())
mixed_bilinear_form += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space(), v=U.extract_sub_space(), form='dual')
mixed_bilinear_form += fncs.PressureIntegrator(ns.pressure, u=P.extract_sub_space(), v=P.extract_sub_space())

A = bilinear_form.assemble()
M = mixed_bilinear_form.assemble()

error_matrix = np.zeros((ndof_u + ndof_p, ndof_u + ndof_p))

for t in time_line.time_points():
    if nonlinear_method == 'explicit':
        bilinear_form_new = fncs.BilinearForm(fes)
        bilinear_form_new += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space(), t=t)
        bilinear_form_new += fncs.ConvectionIntegrator(ns.velocity, u=U.extract_sub_space(), t=t, form='dual')
        bilinear_form_new += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space(), t=t)
        bilinear_form_new += fncs.DiffusionIntegrator(ns.diffusion, u=U.extract_sub_space(), t=t, form='dual')
        bilinear_form_new += fncs.PressureIntegrator(ns.pressure, u=P.extract_sub_space(), t=t)

        A_new = bilinear_form_new.assemble()

        div_matrix = tool.div_matrix(A_new, U.extract_sub_space(), P.extract_sub_space())
        M_new = tool.mass_matrix(U.extract_sub_space())

        source = tool.source(ns.source_term, U.extract_sub_space(), t)

        boundary_condition = ns.dirichlet_boundary_condition(U.extract_sub_space(), t)

        lu = MUMPS(M_new + div_matrix.transpose() @ div_matrix)
        lu.solve(M_new @ U.function.data, source)

        U.function.data += source

        error_matrix = tool.error_matrix(U.extract_sub_space(), ns.exact_solution(ndof_u, t), error_matrix)

        U.function.data -= source

        U.function.data[boundary_condition.indices] = boundary_condition.values

        P.function.data = tool.divergence(U.extract_sub_space(), div_matrix)

        L2_error = np.linalg.norm(error_matrix, ord=2)
        max_error = np.linalg.norm(error_matrix, ord=np.inf)

        print(f't = {t:.4f}, L2_error = {L2_error:.4e}, max_error = {max_error:.4e}')

    elif nonlinear_method == 'implicit':
        # Implement implicit method here
        pass

motion_function = U.function
print(f'sum of absolute values of the motion function: {np.sum(np.abs(motion_function.data)):.4f}')
```