height of colorbar in subplot (matplotlib) - matplotlib

Question

We can change the height and width and position of colorbar by using :
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import make_axes_locatable
import numpy as np
fig = plt.figure()
ax = plt.subplot(111)
im = ax.imshow(np.arange(100).reshape((10, 10)))
c = plt.colorbar(im, cax = fig.add_axes([0.78, 0.5, 0.03, 0.38]))
from here,
I am going to use this in subplots with add_axes and transorm:
fig, axs = plt.subplots(nrows=1, ncols=2)
im0 = axs[0].imshow(np.arange(100).reshape((10, 10)), cmap='afmhot')
c = plt.colorbar(im0, cax=fig.add_axes([0.45, 0.52, 0.03, 0.2],
transform=axs[0].transAxes))
# transform=axs[0].transAxes) does not make any difference
im1 = axs[1].imshow(np.arange(100).reshape((10, 10)), cmap='afmhot_r')
c = plt.colorbar(im1, cax=fig.add_axes([0.87, 0.52, 0.03, 0.2]))
I am going to use transform (transAxes) option to set the location from axes not the figure, but it does not work.

Answer 1

First of all, from the add_axes documentation,
rect : sequence of float
The dimensions [left, bottom, width, height] of the new axes. All quantities are in
fractions of figure width and height.
This is the reason your code doesn't work.
You may instead use an inset_axes.
inset_axes(self, bounds, transform=None, ...)
bounds : [x0, y0, width, height]
Lower-left corner of inset axes, and its width and height.
transform : Transform
Defaults to ax.transAxes, i.e. the units of rect are in axes-relative coordinates.
Here the bounds default to units of axes coordinates, but can be changed if needed.
import matplotlib.pyplot as plt
import numpy as np
fig, ax = plt.subplots()
im = ax.imshow(np.arange(100).reshape((10, 10)))
cax = ax.inset_axes([0.78, 0.5, 0.03, 0.38])
cb = fig.colorbar(im, cax = cax)
plt.show()
An alternative to the above is to use mpl_toolkits.axes_grid1.inset_locator.inset_axes.
import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1.inset_locator import inset_axes
import numpy as np
fig, ax = plt.subplots()
im = ax.imshow(np.arange(100).reshape((10, 10)))
cax = inset_axes(ax, "100%", "100%", bbox_to_anchor=[0.78, 0.5, 0.03, 0.38],
bbox_transform=ax.transAxes, borderpad=0)
cb = fig.colorbar(im, cax = cax)
plt.show()