Plotting with Python

matplotlib and pylab

There are nice tools for making plots of 1d and 2d data (curves, contour plots, etc.) in the module matplotlib. Many of these plot commands are very similar to those in Matlab.

To see some of what’s possible (and learn how to do it), visit the matplotlib gallery. Clicking on a figure displays the Python commands needed to create it.

The best way to get matplotlib working interactively in a standard Python shell is to do:

$ python
>>> import pylab
>>> pylab.interactive(True)

pylab includes not only matplotlib but also numpy. Then you should be able to do:

>>> x = pylab.linspace(-1, 1, 20)
>>> pylab.plot(x, x**2, 'o-')

and see a plot of a parabola appear. You should also be able to use the buttons at the bottom of the window, e.g click the magnifying glass and then use the mouse to select a rectangle in the plot to zoom in.

Alternatively, you could do:

>>> from pylab import *
>>> interactive(True)

With this approach you don’t need to start every pylab function name with pylab, e.g.:

>>> x = linspace(-1, 1, 20)
>>> plot(x, x**2, 'o-')

In these notes we’ll generally use module names just so it’s clear where things come from.

If you use the IPython shell, you can do:

$ ipython --pylab

In [1]: x = linspace(-1, 1, 20)
In [2]: plot(x, x**2, 'o-')

The –pylab flag causes everything to be imported from pylab and set up for interactive plotting.

Mayavi and mlab

Mayavi is a Python plotting package designed primarily for 3d plots. See:

• Documentation
• Gallery

See Downloading and installing software for this class for some ways to install Mayavi.

VisIt

VisIt is an open source visualization package being developed at Lawrence Livermore National Laboratory. It is designed for industrial-strength visualization problems and can deal with very large distributed data sets using MPI.

There is a GUI interface and also a Python interface for scripting.

See:

• Documentation
• Gallery
• Tutorial

ParaView

ParaView is another open source package developed originally for work at the National Labs.

There is a GUI interface and also a Python interface for scripting.

See:

• Documentation
• Gallery