圆锥面

$z = \sqrt{x^2+y^2}$

import matplotlib.pyplot as plt
import numpy as np

x = np.linspace(-5, 5, 101)
y = np.linspace(-5, 5, 101)
X, Y = np.meshgrid(x, y)
Z = np.sqrt(X ** 2 + Y ** 2)

X_below, Y_below = -X, -Y  # 画下半部分
Z_below = -Z

ax = plt.axes(projection='3d')
ax.plot_surface(X, Y, Z, cmap='rainbow')
ax.plot_surface(X_below, Y_below, Z_below, cmap='rainbow')
plt.show()