import numpy as np
import matplotlib.pyplot as plt

[X, Y] = np.mgrid[-2.5:2.5:51j, -3:3:61j]
Z = X**2 - Y**2
curves = plt.contour(X, Y, Z, 12, colors="k")
plt.clabel(curves)
plt.suptitle(r"The level contours of $z=xˆ2-yˆ2$’0", fontsize=20)
plt.show()


plt.contourf(X, Y, Z, 12)
plt.colorbar()
plt.show()


plt.imshow(Z)
plt.show()