import numpy as np
import matplotlib.pyplot as plt

plt.xkcd()
fig = plt.figure( figsize=(6,3.5) )

# the line:
slope = 2.0
xx = np.arange(0.0, 4.1, 0.1)
yy = slope*xx
# the data:
n = 80
rng = np.random.RandomState(218)
sigma = 1.5
x = 4.0*rng.rand(n)
y = slope*x+rng.randn(n)*sigma
# fit:
slopef = np.sum(x*y)/np.sum(x*x)
yf = slopef*xx

# plot it:
ax = fig.add_subplot( 1, 1, 1 )
ax.spines['left'].set_position('zero')
ax.spines['bottom'].set_position('zero')
ax.spines['right'].set_visible(False)
ax.spines['top'].set_visible(False)
ax.get_xaxis().set_tick_params(direction='inout', length=10, width=2)
ax.get_yaxis().set_tick_params(direction='inout', length=10, width=2)
ax.yaxis.set_ticks_position('left')
ax.xaxis.set_ticks_position('bottom')
ax.set_xticks(np.arange(0.0, 4.1))
ax.set_xlim(0.0, 4.2)
#ax.set_ylim(-1, 5)
#ax.set_xticks( np.arange(0, 5))
#ax.set_yticks( np.arange(0, 0.9, 0.2))
ax.set_xlabel('x')
ax.set_ylabel('y')
#ax.annotate('', xy=(mu, 0.02), xycoords='data',
#            xytext=(mu, 0.75), textcoords='data',
#            arrowprops=dict(arrowstyle="->", relpos=(0.5,0.5),
#            connectionstyle=cs), zorder=1 )
ax.scatter(x, y, label='data', s=50, zorder=10)
ax.plot(xx, yy, 'r', lw=6.0, color='#ff0000', label='original', zorder=5)
ax.plot(xx, yf, '--', lw=2.0, color='#ffcc00', label='fit', zorder=7)
ax.legend(loc='upper left', frameon=False)

plt.tight_layout();
plt.savefig('mlepropline.pdf')
#plt.show();