#210 Parametric curve in 3D

import numpy as np
import matplotlib.pyplot as plt
ax = plt.figure().add_subplot(projection='3d')
# Prepare arrays x, y, z
theta = np.linspace(-4 * np.pi, 4 * np.pi, 100)
z = np.linspace(-2, 2, 100)
r = z**2 + 1
x = r * np.sin(theta)
y = r * np.cos(theta)
ax.plot(x, y, z, label='parametric curve')
ax.legend()
plt.savefig('ex210.png', dpi=72)
plt.show()