Matplotlib Colorbar科学记数法偏移

Question

When plotting a colorbar, the top label (I guess this would be called the offset) is mis-centred. This didn't use to happen, I have examples of old code where it was centred above the colorbar, but I have no clue what has changed.

Example:

import numpy as np
import matplotlib.pyplot as plt

z = np.random.random((10,10))

fig, ax = plt.subplots()
im = ax.imshow(z)
cb = fig.colorbar(im)

cb.formatter.set_powerlimits((0, 0))
cb.update_ticks()

plt.show()

Gives this:

As an example of how it used to look (taken from one of my old papers, so different data etc.)

Using the most recent anaconda python 2.7, on MacOSX, mpl version 1.5.0

Edit: I should also note, tight_layout() does not improve this either, though it is missing from the working example.

Answer 1

You can simply use set_offset_position for the y-axis of the colorbar. Compare:

fig, ax = plt.subplots()                
im = ax.imshow(np.random.random((10,10)))                    
cb = fig.colorbar(im)     
cb.formatter.set_powerlimits((0, 0))
cb.ax.yaxis.set_offset_position('right')                         
cb.update_ticks()
plt.show()

versus

fig, ax = plt.subplots()
im = ax.imshow(np.random.random((10,10)))
cb = fig.colorbar(im)
cb.formatter.set_powerlimits((0, 0))
cb.ax.yaxis.set_offset_position('left')
cb.update_ticks()
plt.show()

All in all, it simply looks like the default has changed from right to left.

Answer 2

Using your above code and matplotlib version 1.4.3 I get the following plot

So this may be a version issue. One possible work around could be to use cb.ax.text()

# -*- coding: utf-8 -*-
import numpy as np
import matplotlib.pyplot as plt

z = np.random.random((10,10))

fig, ax = plt.subplots()
im = ax.imshow(z)
cb = fig.colorbar(im)
cb.ax.text(-0.25, 1, r'$\times$10$^{-1}$', va='bottom', ha='left')

plt.show()

This way you have more control over the centring. The above code gives me the following plot Note that I use an r at the start of the string so that $\\times$ produces the correct symbol.