from numpy import *
from scipy.optimize import curve_fit

def func(x, a, b, c):
    return a*exp(-(x-b)**2/(2*c**2))
file = loadtxt("angdist1.xvg", skiprows = 18, dtype = float)
x = []
y = []
for i in range(shape(file)[0]):
    x.append(file[i,0])
    y.append(file[i,1])

popt, pcov = curve_fit(func, x, y)

plt.plot(x, func(x, *popt), color = 'red', linewidth=2)
plt.legend(['Original','fitting'], loc=0)
plt.show()