import numpy as np import matplotlib.pyplot as plt from mpl_toolkits.mplot3d import Axes3D  x, y = np.mgrid[-1:1:31j, -1:1:31j] xs, ys = np.mgrid[-1:1:9j, -1:1:9j]  z = x*np.exp(-x**2 - y**2) zs = xs*np.exp(-xs**2 - ys**2) u = -(1 - 2*xs**2)*np.exp(-xs**2 - ys**2) v = 2*ys*zs w = np.ones_like(xs)  fig = plt.figure() ax = fig.add_subplot(111, projection='3d') ax.view_init(azim=145, elev=45) ax.plot_surface(x, y, z, rstride=1, cstride=1, cmap="summer", lw=0.3,                 edgecolors="k") ax.quiver(xs, ys, zs, u, v, w, colors='k', pivot='tail', length=0.3) plt.axis("off") plt.savefig("Surface normals.svg", bbox_inches="tight", transparent=True) plt.show()