solve(a == L, u, bc)
# Plot solution
# plot(u)
# axi.triplot(u)
vtkfile << u
# Compute error at vertices
# u_e = interpolate(u_D, V)
# error = np.abs(u_e.vector().array() - u.vector().array()).max()
# print('t = %.2f: error = %.3g' % (t, error))
# Update previous solution
u_n.assign(u)
# Compute error in L2 norm
error_L2 = errornorm(u_D, u, 'L2')
# Compute maximum error at vertices
vertex_values_u_D = u_D.compute_vertex_values(mesh)
vertex_values_u = u.compute_vertex_values(mesh)
error_max = np.max(np.abs(vertex_values_u_D - vertex_values_u))
# Print errors
print('error_L2 =', error_L2)
print('error_max =', error_max)
# Hold plot
# interactive()
# plt.show()
