# Vlak

import matplotlib.pyplot as plt
import numpy as np

plt.figure (figsize = (8, 8))

ax = plt.axes (projection = "3d")

phi = np.arange (0, 2 * np.pi, 0.05)
rho = np.arange (0.1, 5, 0.05)

phi, rho = np.meshgrid (phi, rho)
div = np.cos (phi) / (np.sin (phi) * rho)

ax.plot_surface (phi, rho, div, color = "lightgreen")

ax.set_zlim3d (-100, 100)

plt.show ()