#!/usr/bin/python
# -*- coding: utf8 -*-

import matplotlib.pyplot as plt
import matplotlib as mpl
import numpy as np
from math import *

code_website = 'http://commons.wikimedia.org/wiki/User:Geek3/mplwp'
try:
    import mplwp
except ImportError, er:
    print 'ImportError:', er
    print 'You need to download mplwp.py from', code_website
    exit(1)

name = 'mplwp_Fabry-Perot_transmission_R.svg'
fig = mplwp.fig_standard(mpl)

# add pi to xaxis labels
def flabel(x, i):
    if x != int(x):
        return ''
    return u'{}\u03C0'.format(int(x)).replace('-', u'\u2212')
fig.gca().xaxis.set_major_formatter(mpl.ticker.FuncFormatter(flabel))

xlim = 0,5; fig.gca().set_xlim(xlim)
ylim = 0, 1.1; fig.gca().set_ylim(ylim)
mplwp.mark_axeszero(fig.gca())

def Te(delta, R):
    return (1 - R)**2 / (1 + R**2 - 2 * R * cos(delta))

for R in [0.5, 0.8, 0.95]:
    x = np.linspace(xlim[0], xlim[1], 10001)
    y = [Te(xx*pi, R) for xx in x]
    plt.plot(x, y, label='$R={}$'.format(R))

plt.legend(loc='upper left').get_frame().set_alpha(0.9)
plt.savefig(name)
mplwp.postprocess(name)