Subplot_mosaic constrained_layout problem

[laurence.molloy]

Hi Folks,

I’ve been experimenting with the new subplot_mosaic functionality( loving the simplicity, btw) and I’ve hit a problem.

With this layout, constrained_layout=True copes just fine.

layout = “”"
BCCE
BCCE
BADE
“”"
However, with this layout (extending D to a 2x1), I get the warning shown below

layout = “”"
BCCE
BCCE
BADD
“”"

[WARNING]
UserWarning: constrained_layout not applied. At least one axes collapsed to zero width or height.

Can someone explain to me what might cause this?

Incidentally, D is just a stacked bar graph

and E is a simple bar graph.

I also get the same warning when I extend A to (2x1) instead of extending D.

layout = “”"
BCCE
BCCE
BAAD
“”"

Cheers
Laurence

[tacaswell]

Can you try this from the default branch? @jklymak completely re-wrote how the we set up the constraints to avoid this sort of collapse (see https://github.com/matplotlib/matplotlib/pull/17494 for details).

This problem is at the Axes layout level and should be independent of what is in the Axes.

[jklymak]

yes, this indeed fails to converge for 3.3.3, but works fine on master (3.4.0).

The problem here is a difficult one to set up constraints for - the CEAD axes all need to have matching sizes (C==D, A==E) but they do not share inner axes edges. Fixing this case was actually a good whack of relatively complicated code in _constrained_layout.py called _match_submerged_margins. Along with colorbars, it turns what should be 20 lines of code into a few hundred.

[laurence.molloy]

Thanks Thomas/Jody

Useful to know this is a failure mode of the constrained_layouts, and not just something I’ve overlooked in my code.

When is 3.4.0 pencilled in for official release? - It’s not available to me in Google Colab via %pip ATM. (not urgent - just a request for info)

Cheers
Laurence