From 29f2e5c7874eb9ff8efd66e2e3c82e4519562a27 Mon Sep 17 00:00:00 2001
From: Richard Murray <murray@cds.caltech.edu>
Date: Thu, 30 Dec 2021 22:28:33 -0800
Subject: [PATCH] add documentation about use of axis('equal') in pzmap, rlocus
---
control/pzmap.py | 11 +++++++++--
control/rlocus.py | 8 ++++++++
2 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/control/pzmap.py b/control/pzmap.py
index d1323e103..ae8db1241 100644
--- a/control/pzmap.py
+++ b/control/pzmap.py
@@ -59,8 +59,7 @@
# http://matplotlib.sourceforge.net/examples/axes_grid/demo_axisline_style.html
# http://matplotlib.sourceforge.net/examples/axes_grid/demo_curvelinear_grid.html
def pzmap(sys, plot=None, grid=None, title='Pole Zero Map', **kwargs):
- """
- Plot a pole/zero map for a linear system.
+ """Plot a pole/zero map for a linear system.
Parameters
----------
@@ -78,6 +77,14 @@ def pzmap(sys, plot=None, grid=None, title='Pole Zero Map', **kwargs):
The systems poles
zeros: array
The system's zeros.
+
+ Notes
+ -----
+ The pzmap function calls matplotlib.pyplot.axis('equal'), which means
+ that trying to reset the axis limits may not behave as expected. To
+ change the axis limits, use matplotlib.pyplot.gca().axis('auto') and
+ then set the axis limits to the desired values.
+
"""
# Check to see if legacy 'Plot' keyword was used
if 'Plot' in kwargs:
diff --git a/control/rlocus.py b/control/rlocus.py
index 4b1af57f7..23122fe72 100644
--- a/control/rlocus.py
+++ b/control/rlocus.py
@@ -114,6 +114,14 @@ def root_locus(sys, kvect=None, xlim=None, ylim=None,
Computed root locations, given as a 2D array
klist : ndarray or list
Gains used. Same as klist keyword argument if provided.
+
+ Notes
+ -----
+ The root_locus function calls matplotlib.pyplot.axis('equal'), which
+ means that trying to reset the axis limits may not behave as expected.
+ To change the axis limits, use matplotlib.pyplot.gca().axis('auto') and
+ then set the axis limits to the desired values.
+
"""
# Check to see if legacy 'Plot' keyword was used
if 'Plot' in kwargs: