"""
Contour plot of the Himmelblau function.
"""
from __future__ import division
import numpy as np
import matplotlib.pyplot as plt
from matplotlib import rcParams

rcParams['font.size'] = 12

npts = 201
x, y = np.mgrid[-6:6:npts*1j, -6:6:npts*1j]
z = (x**2 + y - 11)**2 + (x + y**2 - 7)**2

fig = plt.figure(figsize=(5, 5))
levels = np.logspace(0.3, 3.5, 15)
plt.contour(x, y, z, levels, cmap="viridis")
plt.xlabel(r"$x$", fontsize=14)
plt.ylabel(r"$y$", fontsize=14)
plt.xticks([-6, -3, 0, 3, 6])
plt.yticks([-6, -3, 0, 3, 6])
plt.xlim([-6, 6])
plt.ylim([-6, 6])
plt.savefig("Himmelblau_contour.svg", bbox_inches="tight")
plt.show()