eps_eq = [   9.9484608457   0.0000000000   0.0000000000
             0.0000000000   9.9484608457   0.0000000000
             0.0000000000   0.0000000000   9.9484608457];
eps_pos = [  9.9488281596   0.0000000009   0.0000000009
             0.0000000004   9.9486321634  -0.0133978975
             0.0000000004  -0.0133978970   9.9486321630];
eps_neg = [  9.9488281561   0.0000000000   0.0000000000
             0.0000000000   9.9486321602   0.0133978972
             0.0000000000   0.0133978972   9.9486321602];

dchi_dtau = (eps_pos - eps_neg)/(0.02*4*%pi);
disp(dchi_dtau)

quit
