PR summary

Discovered when I was trying to wrap my head around#30089. Given

importmatplotlib.pyplotaspltmosaic1="AC;BC"mosaic2="ACDE;BCDE"formosaicinmosaic1,mosaic2:fig,ax_dir=plt.subplot_mosaic(mosaic,layout='constrained',facecolor='skyblue')fig.get_layout_engine().set(h_pad=0.2)plt.show()

Onmain, the gap between the rows of the first column is larger when there are more other columns

Currently the "submerged margins" function works out the required size of the margin by summing the main margin and the "cb" margin (which includes our initial pad). If I have understood, we then apply that required size to only the main margin. So the "cb" margin size gets added on each time we pass through the loop.

Here I just subtract the "cb" values we started with from the target margin size. So the total margin should be what we are aiming for. So the above code now gives:

Given that some test images changed, I'm unsure if this would count as an API change.

PR checklist

• [n/a] "closes #0000" is in the body of the PR description tolink the related issue
• new and changed code istested
• [n/a]Plotting related features are demonstrated in anexample
• New Features andAPI Changes are noted with adirective and release note
• Documentation complies withgeneral anddocstring guidelines