import matplotlib.pyplot as plt
from numpy import *
def optical_force(mpb_data):
wavg = 0.5*(mpb_data[:-1,1]+mpb_data[1:,1])
dw = mpb_data[1:,1]-mpb_data[:-1,1]
vg = 0.5*(mpb_data[:-1,2]+mpb_data[1:,2])
ds = mpb_data[1,0]-mpb_data[0,0]
return multiply(multiply(-1/wavg, dw/ds), 1/vg)
odd_data = genfromtxt('parallel-wvgs-yodd.dat', delimiter=",");
force_odd = optical_force(odd_data)
s_odd = odd_data[:-1,0]
even_data = genfromtxt('parallel-wvgs-yeven.dat', delimiter=",");
force_even = optical_force(even_data)
s_even = even_data[:-1,0]
plt.plot(s_odd,force_odd,'b-',label='antisymmetric');
plt.plot(s_even,force_even,'r-',label='symmetric');
plt.xlabel("waveguide separation s/a");
plt.ylabel("optical force (F/L)(ac/P)");
plt.legend(loc='upper right');
plt.xticks(arange(0,1.2,0.2));
plt.yticks(arange(-1.5,1.0,0.5));
plt.show()