#!/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_Langevin-function.svg'
fig = mplwp.fig_standard(mpl)

xlim = -10,10; fig.gca().set_xlim(xlim)
ylim = -1.1,1.1; fig.gca().set_ylim(ylim)
mplwp.mark_axeszero(fig.gca())

def L(x):
    if abs(x) < 1e-6:
        return x / 3.0
    return 1.0 / tanh(x) - 1.0 / x
x = np.linspace(xlim[0], xlim[1], 5001)
y = [L(xx) for xx in x]
plt.plot(x, y, label='L(x)')

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