from numpy import *
import matplotlib.pyplot as plt

f = genfromtxt("modes.dat", delimiter=",")
plt.plot(f[:,0],f[:,1:],'b-',f[:,0],f[:,0],'k-')
plt.xlabel("wavevector k_x (units of 2π/a)")
plt.ylabel("frequency (units of 2πc/a)")
plt.axis([0,0.5,0,0.4])
plt.xticks([t for t in np.arange(0,0.6,0.1)])
plt.yticks([t for t in np.arange(0,0.5,0.1)])
plt.show()