"""
This code will not show an animation, but will save an image file
for each frame, which can later be turned into a movie
by external software, for instance from the ImageMagick suite.
"""

import numpy as np
import matplotlib.pyplot as plt

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

m = 0   #midpoint of curve

"""
We will animate how the curve changes shape as s goes from
2 to 0.2, so we create an array of s values in this interval:
"""
s_start = 2
s_stop = 0.2
s_values = np.linspace(s_start,s_stop,20)

x = np.linspace(-3*s_start,3*s_start,100)

#calculate the highest value  of f and fix the axes
f_max = f(m,m,s_stop)
plt.axis([-3*s_start,3*s_start,0,f_max])

y = f(x,m,s_start)
"""
We want to update the plot, so we keep the object return
from plt.plot in a variable:"""
lines = plt.plot(x,y)

# we need a counter to create unique filenames:
counter = 0

"""
for loop over s values to update the y data, draw the
plot and save it to file:"""
for s in s_values:
    y = f(x,m,s)
    lines[0].set_ydata(y)
    plt.draw()
    plt.savefig('tmp_%04d.png' %(counter))
    counter += 1

"""
Terminal> python animate_gauss2.py
(No plot is shown, but a number of files named "tmp_xxxx.png" should
be created. These can be combined into a movie with external software.)
"""