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Add documentation about use of axis('equal') in pzmap, rlocus #685

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11 changes: 9 additions & 2 deletions control/pzmap.py
Original file line number Diff line number Diff line change
Expand Up @@ -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
----------
Expand All @@ -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:
Expand Down
8 changes: 8 additions & 0 deletions control/rlocus.py
Original file line number Diff line number Diff line change
Expand Up @@ -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:
Expand Down