Frad = 1e-12 * (1 - rad / L) * np.exp(-rad / L)
Fx = -np.sin(phi) * Fphi + np.cos(phi) * Frad
Fy = np.cos(phi) * Fphi + np.sin(phi) * Frad
return np.array([Fx, Fy])
sim = fokker_planck(temperature=300,
drag=drag,
extent=[800 * nm, 800 * nm],
resolution=10 * nm,
boundary=boundary.reflecting,
force=F)
### time-evolved solution
pdf = gaussian_pdf(center=(-150 * nm, -150 * nm), width=30 * nm)
p0 = pdf(*sim.grid)
Nsteps = 200
time, Pt = sim.propagate_interval(pdf, 20e-3, Nsteps=Nsteps)
### animation
fig = plt.figure(figsize=plt.figaspect(1 / 2))
ax1 = fig.add_subplot(1, 2, 1, projection='3d')
surf = ax1.plot_surface(*sim.grid / nm, p0, cmap='viridis')
ax1.set_zlim([0, np.max(Pt) / 5])
ax1.autoscale(False)
ax1.set(xlabel='x (nm)', ylabel='y (nm)', zlabel='normalized PDF')
L = 20 * nm
F = lambda x: 5e-21 * (np.sin(x / L) + 4) / L
sim = fokker_planck(temperature=300,
drag=drag,
extent=600 * nm,
resolution=10 * nm,
boundary=boundary.periodic,
force=F)
### steady-state solution
steady = sim.steady_state()
### time-evolved solution
pdf = gaussian_pdf(-150 * nm, 30 * nm)
p0 = pdf(sim.grid[0])
Nsteps = 200
time, Pt = sim.propagate_interval(pdf, 2e-3, Nsteps=Nsteps)
### animation
fig, ax = plt.subplots(constrained_layout=True)
ax.plot(sim.grid[0] / nm,
p0,
color='red',
ls='--',
alpha=.3,
lw=2,
label='initial PDF')
ax.plot(sim.grid[0] / nm,