[Bug]: Layout Managers are confused by complex arrangement of sub-figures and gridspec's #30076

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1. tacaswell commented on May 19, 2025

   

   tacaswell

   on May 19, 2025

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   I have seen similar things with code that set a fixed aspect ratio and manually adjusted the locations before running the layout code.

   dropping to either the figures rows or cols being 1 makes it work and

   import matplotlib.pyplot as plt
   
   
   def test(layout):
       fig = plt.figure(figsize=(12, 16), layout=layout)
       figures = fig.subfigures(4, 2)
       fig.suptitle(layout)
       for f in figures.flatten():
           axd = fig.subplot_mosaic('AD;BD;CD')
           for ax in axd.values():
               ax.plot()
       # fig.savefig(layout + ".png")
   
   
   test("compressed")
   test("constrained")
   test("none")
   test("tight")

   is broken even worse
2. tacaswell

   added this to the v3.11.0 milestone on May 19, 2025
3. tacaswell

   added

   status: confirmed bug

   on May 19, 2025
4. jklymak commented on May 19, 2025

   

   jklymak

   on May 19, 2025

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   Hmmm, well somehow the margin for the first subfigure is the starting point for the second figure, and then the margin gets made even larger for the second.

   import matplotlib.pyplot as plt
   
   
   
   def test(layout, labelled=False):
       ll = labelled
       fig = plt.figure(figsize=(4, 5), layout=layout)
       fig.suptitle(f'Labelled = {not labelled}', fontsize='small')
       figures = fig.subfigures(2, 1)
       for f in figures.flatten():
           gs = f.add_gridspec(2, 2)
           for i in range(2):
               ax = f.add_subplot(gs[i, 0])
               ax.plot()
               if not labelled:
                   ax.set_xlabel('BOOO', fontsize='large')
                   labelled = True
           f.add_subplot(gs[:, 1]).plot()
       fig.savefig(f'fig_{not ll}.png')
   test("constrained")
   test("constrained", labelled=True)
   plt.show()
   

   No label

   

   big label

   
5. jklymak commented on May 19, 2025

   

   jklymak

   on May 19, 2025

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   I played with this for a while, and I do not see any obvious error in the logic.

   At its root, I think this is a limitation with the we we have chosen to set up the constraint solver, in that the behaviour above is following the constraints we have given it, but they are not rigorous enough to narrow the gap.

   I appreciate that it would be more sensible for the subfigures to not care about each other's layout, but practically, that is not how the constraint engine is set up, and the constraints are all solved at the same time.

   If you want deterministic behaviour here without changing the internals of constrained layout, you can simply create more subfigures so that the left-hand axes are not tied to what the right-hand column is doing:

   import matplotlib.pyplot as plt
   
   def test(layout):
       fig = plt.figure(figsize=(4, 5), layout='constrained')
       figures = fig.subfigures(2, 1)
       figures[0].set_facecolor('grey')
       figures[1].set_facecolor('red')
       for nn, f in enumerate(figures.flatten()):
           ffigs = f.subfigures(1, 2)
           ffigs[0].set_facecolor('lightgreen')
           ax = ffigs[0].subplots(2, 1)
           for i in range(2):
               ax[i].plot()
               if (nn==0) and (i == 0):
                   ax[i].set_xlabel('BOOOOO', fontsize=20)
           ffigs[1].set_facecolor('lightblue')
           ax = ffigs[1].add_subplot()
           ax.plot()
       fig.savefig(f'Fixed.png')
   
   test("constrained")
   plt.show()

   

   We can keep this open, but not sure anything will be done about it in the near future. If we were to do anything, it might be to try and make subfigure1 independent of subfigure2. The other thing that could be improved is the assignment of space between axes in one column when the other column does not have any axes spines at that row (eg the case here). That case is mildly under constrained, and as shown here doesn't work consistently.
6. jklymak

   added

   topic: geometry managerLayoutEngine, Constrained layout, Tight layoutLayoutEngine, Constrained layout, Tight layout

   on May 19, 2025
7. jklymak commented on May 20, 2025

   

   jklymak

   on May 20, 2025

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   Actually I found the bug #30089 is an easy fix.
8. rcomer

   closed this as completedin #30089on May 25, 2025
9. rcomer

   modified the milestones: v3.11.0, v3.10.4 on May 25, 2025