6. Animations

• Download the full notebook [v2]
• Download the teaching notebook [v2]

Use the “v2” files in older versions of IPython, e.g. 0.12

Matplotlib Tutorial: 6. Animations

Matplotlib 1.1 introduced the animation framework: the following will only work with this newest version. This is a backend-independent framework for creating animated plots, and is very powerful (for some interesting examples, see the blog posts here and here)

Here we'll just create a basic example of an animated sine wave.

Here it's vital that we don't use pylab inline mode, because the inline figures are static.

In [1]:

%pylab
from matplotlib import animation

Welcome to pylab, a matplotlib-based Python environment [backend: TkAgg].
For more information, type 'help(pylab)'.

There are a few different ways to call the animator. ArtistAnimation animates a list of artist elements, showing only one at a time. TimedAnimation can be subclassed to create very flexible animations. FuncAnimation animates using a user-defined function which updates the plot elements at each frame step. We'll use FuncAnimation below, because it makes very clear how the animations work.

In [2]:

# First set up the figure, the axis, and the plot element we want to animate
fig, ax = plt.subplots()
ax.set_xlim(0, 2)
ax.set_ylim(-2, 2)

x = np.linspace(0, 2, 1000)
y = np.zeros_like(x)

line, = ax.plot(x, y, lw=2)

# initialization function: plot the background of each frame
def init():
    line.set_data([], [])
    return line,

# animation function.  This is called sequentially
def animate(i):
    y = np.sin(2 * np.pi * (x - 0.01 * i))
    line.set_data(x, y)
    return line,

# call the animator.  blit=True means only re-draw the parts that have changed.
anim = animation.FuncAnimation(fig, animate, init_func=init,
                               frames=200, interval=20, blit=True)

# save the animation as an mp4.  This requires ffmpeg or mencoder to be
# installed.  The codec argument ensure that the x264 codec is used, so that
# the video can be embedded in html5.  You may need to adjust this for
# your system: for more information, see
# http://matplotlib.sourceforge.net/api/animation_api.html
#anim.save('basic_animation.mp4', fps=30, codec='libx264')

Exercise: Modify the above code to add a second wave which travels to the left rather than to the right.