imshow in subplot with interactive mode

Question

I cannot get matshow() or imshow() to actually display the plot when both of the following conditions are true: (1) interactive mode is on: import matplotlib.pyplot as plot; plot.ion(), and (2) I am trying to use matshow on a specific subplot: fig = plot.figure(); ax = fig.add_subplot(111); ax.matshow([[1,2],[3,0]]).

Using plot.matshow([[1,2],[3,0]]) (note: no explicit axes) works find in interactive mode, but will always create a new figure window with a single axes object. The above code with the subplot also works fine without interactive mode using plot.show(), and will put the image on the correct axes.

More oddly, the above code with the subplot will show the image if I interact with the figure, such as by using the zoom tool and clicking randomly in the figure window (there is no visible axes object, but I just click somewhere in the middle of the figure window).

Any ideas what might be causing this, how I could fix it, or how I could get around it to use matshow or imshow on a specified subplot (the end use case is to have more than 1 subplot in the figure)? This occurs in python (2.7.6) and ipython (1.1.1)

DrV DrV · Accepted Answer · 2014-07-02T21:01:36

This may have something to do with this documentation:

Display an array as a matrix in a new figure window.

However, you may as well use imshow with suitable arguments:

import matplotlib.pyplot as plt

plt.imshow(mat, interpolation='nearest', origin='upper', aspect='equal')

This should do the same thing while being a bit less odd. This is actually exactly what matshow does internally. It just adds a few tick markers to the image.

Also, by having a look at the source (or closely reading the help string), you may try to do:

plt.matshow(mat, fignum=0)

This should force it use current axis, which it picks by using gca.

In addition to this, there is ax.matshow which you used, as well. Actually plt.matshow is a very thin wrapper around ax.matshow, mostly to create the new image.

If you still have problems with matshow or imshow in subplots, please make a minimal complete example for us to try! Here is something I tried in the interactive shell (IPython):

figure()
ax = subplot(121)
ax2 = subplot(122)
ax.matshow(random.random((20,30)))
ax2.plot(linspace(-1,1,100), linspace(-1,1,100)**2)
draw()

(Could the problem be a missing draw?)

What I got:

enter image description here

imshow in subplot with interactive mode

1 Answers