'''

================

Parametric Curve

================

This example demonstrates plotting a parametric curve in 3D.

'''

# This import registers the 3D projection, but is otherwise unused.

from mpl_toolkits.mplot3d import Axes3D # noqa: F401 unused import

import numpy as np

import matplotlib.pyplot as plt

plt.rcParams['legend.fontsize'] = 10

fig = plt.figure()

ax = fig.gca(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.show()