from mpl_toolkits.mplot3d import Axes3D
from matplotlib import cm
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure(figsize=(10,10))
ax = fig.add_subplot(111, projection="3d")
ax.set_xlabel("x")
ax.set_ylabel("y")
ax.set_zlabel("z")

X = np.arange(-15, 15, 0.5)
Y = np.arange(-15, 15, 0.5)
X, Y = np.meshgrid(X, Y)
Z = -(X**2 + Y**3)

surf = ax.plot_surface(X, Y, Z, rstride=1, cstride=1, cmap=cm.jet, linewidth=0, antialiased=True)

plt.show()