"""
Animation recipe 2.
Instead of viewing the individual plots we save them in 
files with unique filenames. Then we can use external 
software, for instance from the ImageMagick suite, 
to create a movie file from the images.
"""

import matplotlib.pyplot as plt
import numpy as np

def f(x, m, s):
    return (1.0/(np.sqrt(2*np.pi)*s))*np.exp(-0.5*((x-m)/s)**2)

m = 0;  s_start = 2;  s_stop = 0.2
s_values = np.linspace(s_start, s_stop, 30)

x = np.linspace(m -3*s_start, m + 3*s_start, 1000)

# Largest f is at the midpoint (x=m) and for the smallest values of s
max_f = f(m, m, s_stop)

y = f(x,m,s_stop)
lines = plt.plot(x,y)

plt.axis([x[0], x[-1], -0.1, max_f])
plt.xlabel('x')
plt.ylabel('f')

frame_counter = 0
for s in s_values:
    y = f(x, m, s)
    lines[0].set_ydata(y) # update plot data for the new image
    plt.draw()
    plt.savefig(f'tmp_{frame_counter:04d}.png') # unique file name
    frame_counter += 1