def test_sim(do_plot=False):
mesh = df.BoxMesh(0, 0, 0, 2, 2, 2, 1, 1, 1)
sim = Sim(mesh, 8.6e5, unit_length=1e-9)
alpha = 0.1
sim.alpha = alpha
sim.set_m((1, 0, 0))
sim.set_up_solver()
H0 = 1e5
sim.add(Zeeman((0, 0, H0)))
exchange = Exchange(13.0e-12)
sim.add(exchange)
dt = 1e-12
ts = np.linspace(0, 500 * dt, 100)
precession_coeff = sim.gamma / (1 + alpha**2)
mz_ref = []
mz = []
real_ts = []
for t in ts:
sim.run_until(t)
real_ts.append(sim.t)
mz_ref.append(np.tanh(precession_coeff * alpha * H0 * sim.t))
mz.append(sim.m[-1]) # same as m_average for this macrospin problem
mz = np.array(mz)
if do_plot:
ts_ns = np.array(real_ts) * 1e9
plt.plot(ts_ns, mz, "b.", label="computed")
plt.plot(ts_ns, mz_ref, "r-", label="analytical")
plt.xlabel("time (ns)")
plt.ylabel("mz")
plt.title("integrating a macrospin")
plt.legend()
plt.savefig(os.path.join(MODULE_DIR, "test_sllg.png"))
print("Deviation = {}, total value={}".format(np.max(np.abs(mz - mz_ref)),
mz_ref))
assert np.max(np.abs(mz - mz_ref)) < 8e-7
