# Vlak

import matplotlib.pyplot as plt
import numpy as np

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

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

y = np.arange (-2, 2, 0.05)
z = np.arange (-2, 2, 0.05)

y, z = np.meshgrid (y, z)
u = y**2 + 3 * z**2

ax.plot_surface (y, z, u, color = "red")

plt.show ()