too much white space around Root Locus with omega-damping grid

When I turn on the omega-damping grid for root locus plot with grid=True (turned on by default), it adds too much white space around the actual plot, which is very annoying. With this grid turned off, plot is tight and nice.

I would like root locus to not have this extra white space around when grid is turned on, I am pretty sure this is some sort of platform-specific bug. Would appreciate any help 🙏

grid turned on (probably bug):

grid turned off (expected behavior):

Libraries:

control 0.10.1
matplotlib 3.10.0

I'm using python control in Google Colab.

I cannot reproduce on the current tip of main branch, so this must have been fixed already. There is a new release coming soon: #1130

@slivingston

@slivingston Did you run inside a Jupyter notebook? What version?

I tried running this using the following versions and got the same problem as @datacurse noted:

IPython          : 8.31.0
ipykernel        : 6.29.5
ipywidgets       : 8.1.5
jupyter_client   : 8.6.3
jupyter_core     : 5.7.2
jupyter_server   : 2.14.2
jupyterlab       : 4.3.3
nbclient         : 0.10.1
nbconvert        : 7.16.4
nbformat         : 5.10.4
notebook         : 7.3.1
qtconsole        : not installed
traitlets        : 5.14.3

I also tried running this on Colab and I get the same problem using the following commands:

!pip install git+https://github.com/python-control/python-control.git

import control as ct
import matplotlib.pyplot as plt

sys = ct.tf([1, 2], [1, 0, 0])
cplt = ct.root_locus(sys, grid=True)

No, I ran it in IPython in a terminal, so the Matplotlib backend would be different. I just tried in Colab and reproduced it (like you), so now I think it is something new.

With matplotlib 3.10.0, I can reproduce this. (Also happens in Colab, at time of writing, and Colab is also running matplotlib 3.10.0)

With matplotlib 3.11.0, there's no extra whitespace, but the damping grid lines look wrong.

Other installed packages at end; apologies for long list, I also installed jupyterlab.

matplotlib 3.10.0

matplotlib 3.11.0

packages

changing matplotlib versions didn't result in any upgrade or downgrade of other packages. This list is for matplotlib 3.11.0.

Package                   Version                 Editable project location
------------------------- ----------------------- ------------------------------
anyio                     4.14.1
argon2-cffi               25.1.0
argon2-cffi-bindings      25.1.0
arrow                     1.4.0
asttokens                 3.0.1
async-lru                 2.3.0
attrs                     26.1.0
babel                     2.18.0
beautifulsoup4            4.15.0
bleach                    6.4.0
certifi                   2026.6.17
cffi                      2.1.0
charset-normalizer        3.4.9
comm                      0.2.3
contourpy                 1.3.3
control                   0.10.3.dev20+g7d5019e0b /home/roryy/src/python-control
cycler                    0.12.1
debugpy                   1.8.21
decorator                 5.3.1
defusedxml                0.7.1
executing                 2.2.1
fastjsonschema            2.21.2
fonttools                 4.63.0
fqdn                      1.5.1
h11                       0.16.0
httpcore                  1.0.9
httpx                     0.28.1
idna                      3.18
ipykernel                 7.3.0
ipython                   9.15.0
ipython_pygments_lexers   1.1.1
isoduration               20.11.0
jedi                      0.20.0
Jinja2                    3.1.6
json5                     0.15.0
jsonpointer               3.1.1
jsonschema                4.26.0
jsonschema-specifications 2025.9.1
jupyter_builder           1.1.0
jupyter_client            8.9.1
jupyter_core              5.9.1
jupyter-events            0.12.1
jupyter-lsp               2.3.1
jupyter_server            2.20.0
jupyter_server_terminals  0.5.4
jupyterlab                4.6.1
jupyterlab_pygments       0.3.0
jupyterlab_server         2.28.0
kiwisolver                1.5.0
lark                      1.3.1
MarkupSafe                3.0.3
matplotlib                3.11.0
matplotlib-inline         0.2.2
mistune                   3.3.3
nbclient                  0.11.0
nbconvert                 7.17.1
nbformat                  5.10.4
nest-asyncio2             1.7.2
notebook                  7.6.0
notebook_shim             0.2.4
numpy                     2.5.1
packaging                 26.2
pandocfilters             1.5.1
parso                     0.8.7
pexpect                   4.9.0
pillow                    12.3.0
pip                       25.1.1
platformdirs              4.10.0
prometheus_client         0.25.0
prompt_toolkit            3.0.52
psutil                    7.2.2
ptyprocess                0.7.0
pure_eval                 0.2.3
pycparser                 3.0
Pygments                  2.20.0
pyparsing                 3.3.2
python-dateutil           2.9.0.post0
python-json-logger        4.1.0
PyYAML                    6.0.3
pyzmq                     27.1.0
referencing               0.37.0
requests                  2.34.2
rfc3339-validator         0.1.4
rfc3986-validator         0.1.1
rfc3987-syntax            1.1.0
rpds-py                   2026.6.3
scipy                     1.18.0
Send2Trash                2.1.0
six                       1.17.0
soupsieve                 2.8.4
stack-data                0.6.3
terminado                 0.18.1
tinycss2                  1.5.1
tornado                   6.5.7
traitlets                 5.15.1
typing_extensions         4.16.0
tzdata                    2026.3
uri-template              1.3.0
urllib3                   2.7.0
wcwidth                   0.8.2
webcolors                 25.10.0
webencodings              0.5.1
websocket-client          1.9.0

control's grid.py defines ModifiedExtremeCycleFinder, subclassing matplotlib's angle_helper.ExtremeFinderCycle, and overrides __call__. ExtremeFinderCycle is a subclass of ExtremeFinderSimple.

Somewhere between matplotlib 3.10.0 and 3.11.0, matplotlib moved the extreme finder logic into _find_transformed_bbox, which is called by ExtremeFinderSimple's __call__, and _find_transformed_bbox is directly called in some places, e.g., GridFinder.get_grid_info. In control, _find_transformed_bbox is not overridden, so we're getting the "finder" behaviour of ExtremeFinderCycle.

See https://gist.github.com/roryyorke/655741c97b6bb6062f6fcb037151cac1/revisions for diff of grid_finder.py between 3.10.0 and 3.11.0 (this is "by-hand" created in Github gist; Github doesn't have easily accessible file-diff-between-version capability).

I did a cursory search of matplotlib's issues for ExtremeFinderSimple and _find_transformed_bbox, but nothing is mentioned. The docs for this corner of matplotlib are a bit thin.

Anyway, the fix on the control side is to move the calcs in ModifiedExtremeCycleFinder.__call__ to _find_transformed_bbox, and (to be confirmed) just omit the __call__ override.

That doesn't solve the extra whitespace question for Matplotlib 3.10.0, of course - I've hijacked the discussion around that a bit, sorry.

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too much white space around Root Locus with omega-damping grid #1147

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too much white space around Root Locus with omega-damping grid #1147

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slivingston commented on Apr 26, 2025

murrayrm commented on Apr 26, 2025

slivingston commented on Apr 26, 2025

roryyorke commented on Jul 11, 2026

matplotlib 3.10.0

matplotlib 3.11.0

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roryyorke commented on Jul 12, 2026

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