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

fig = plt.figure()
ax = fig.add_subplot(111)
x= np.linspace(-math.pi,math.pi,30)
y= np.linspace(-math.pi,math.pi,30)
xx,yy = np.meshgrid(x,y)

X_grid, Y_grid = np.meshgrid(x,y)
print("X_grid shape: ",X_grid.shape)
zz =-2*(np.cos(xx) + np.cos(yy))

#ax = plt.axes(projection='3d')
ax = Axes3D(fig)
ax.plot_surface(xx,yy,zz)

plt.xticks([x[0],x[int(len(s)/2)], x[-1]], [r'$-\pi$',  r'$0$', r'$-\pi$' ])
plt.yticks([y[0],y[int(len(s)/2)], y[-1]], [r'$-\pi$',  r'$0$', r'$-\pi$' ])
plt.xlabel("kx")
plt.ylabel("ky")