Bug summary

Updating a GridSpec's width or height ratios after axes have already been added to it has no visible effect — the figure layout silently stays unchanged, even though the internal state is updated correctly.

Code for reproduction

import matplotlib.pyplot as plt
import matplotlib.gridspec as gridspec

fig = plt.figure()
gs = gridspec.GridSpec(1, 3, figure=fig, width_ratios=[1, 2, 1])
ax1 = fig.add_subplot(gs[0, 0])
ax2 = fig.add_subplot(gs[0, 1])
ax3 = fig.add_subplot(gs[0, 2])
fig.canvas.draw()

print("Before:", round(ax2.get_position().width, 4))

gs.set_width_ratios([1, 1, 1])
fig.canvas.draw()

print("After: ", round(ax2.get_position().width, 4))

fig.savefig('test.png')
plt.show()

Actual outcome

Before: 0.3419
After: 0.3419

Expected outcome

After the ratios are updated, all three axes should become equal width:

Before: 0.3419
After: 0.2279

Additional information

No response

Operating system

Ubuntu 24.04

Matplotlib Version

3.12.0.dev230+g1845e6647

Matplotlib Backend

tkagg

Python version

3.12.3

Jupyter version

No response

Installation

git checkout