Frontpage contour example

This example reproduces the frontpage contour example.

import matplotlib.pyplot as plt
import numpy as np
from matplotlib import cm

extent = (-3, 3, -3, 3)

delta = 0.5
x = np.arange(-3.0, 4.001, delta)
y = np.arange(-4.0, 3.001, delta)
X, Y = np.meshgrid(x, y)
Z1 = np.exp(-X**2 - Y**2)
Z2 = np.exp(-(X - 1)**2 - (Y - 1)**2)
Z = Z1 - Z2

norm = cm.colors.Normalize(vmax=abs(Z).max(), vmin=-abs(Z).max())

fig, ax = plt.subplots()
cset1 = ax.contourf(
    X, Y, Z, 40,
    norm=norm)
ax.set_xlim(-2, 2)
ax.set_ylim(-2, 2)
ax.set_xticks([])
ax.set_yticks([])
fig.savefig("contour_frontpage.png", dpi=25)  # results in 160x120 px image
plt.show()