# View more python tutorials on my Youtube and Youku channel!!!

# Youtube video tutorial: https://www.youtube.com/channel/UCdyjiB5H8Pu7aDTNVXTTpcg

# Youku video tutorial: http://i.youku.com/pythontutorial

# 8 - annotation

"""

Please note, this script is for python3+.

If you are using python2+, please modify it accordingly.

Tutorial reference:

http://www.scipy-lectures.org/intro/matplotlib/matplotlib.html

Mathematical expressions:

http://matplotlib.org/users/mathtext.html#mathtext-tutorial

"""

import matplotlib.pyplot as plt

import numpy as np

x = np.linspace(-3, 3, 50)

y = 2*x + 1

plt.figure(num=1, figsize=(8, 5),)

plt.plot(x, y,)

ax = plt.gca()

ax.spines['right'].set_color('none')

ax.spines['top'].set_color('none')

ax.spines['top'].set_color('none')

ax.xaxis.set_ticks_position('bottom')

ax.spines['bottom'].set_position(('data', 0))

ax.yaxis.set_ticks_position('left')

ax.spines['left'].set_position(('data', 0))

x0 = 1

y0 = 2*x0 + 1

plt.plot([x0, x0,], [0, y0,], 'k--', linewidth=2.5)

plt.scatter([x0, ], [y0, ], s=50, color='b')

# method 1:

#####################

plt.annotate(r'$2x+1=%s$' % y0, xy=(x0, y0), xycoords='data', xytext=(+30, -30),

             textcoords='offset points', fontsize=16,

             arrowprops=dict(arrowstyle='->', connectionstyle="arc3,rad=.2"))

# method 2:

########################

plt.text(-3.7, 3, r'$This\ is\ the\ some\ text. \mu\ \sigma_i\ \alpha_t$',

         fontdict={'size': 16, 'color': 'r'})

plt.show()