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fix rlocus timeout due to inefficient _default_wn calculation #527

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Merged
merged 1 commit into from
Feb 5, 2021
Merged

fix rlocus timeout due to inefficient _default_wn calculation #527

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28 changes: 18 additions & 10 deletions control/rlocus.py
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Original file line number Diff line number Diff line change
Expand Up @@ -646,8 +646,9 @@ def _sgrid_func(fig=None, zeta=None, wn=None):
else:
ax = fig.axes[1]

# Get locator function for x-axis tick marks
# Get locator function for x-axis, y-axis tick marks
xlocator = ax.get_xaxis().get_major_locator()
ylocator = ax.get_yaxis().get_major_locator()

# Decide on the location for the labels (?)
ylim = ax.get_ylim()
Expand Down Expand Up @@ -690,7 +691,7 @@ def _sgrid_func(fig=None, zeta=None, wn=None):
# omega-constant lines
angles = np.linspace(-90, 90, 20) * np.pi/180
if wn is None:
wn = _default_wn(xlocator(), ylim)
wn = _default_wn(xlocator(), ylocator())

for om in wn:
if om < 0:
Expand Down Expand Up @@ -746,7 +747,7 @@ def _default_zetas(xlim, ylim):
return zeta.tolist()


def _default_wn(xloc, ylim):
def _default_wn(xloc, yloc, max_lines=7):
"""Return default wn for root locus plot

This function computes a list of natural frequencies based on the grid
Expand All @@ -758,23 +759,30 @@ def _default_wn(xloc, ylim):
List of x-axis tick values
ylim : array_like
List of y-axis limits [min, max]
max_lines : int, optional
Maximum number of frequencies to generate (default = 7)

Returns
-------
wn : list
List of default natural frequencies for the plot

"""
sep = xloc[1]-xloc[0] # separation between x-ticks

# Decide whether to use the x or y axis for determining wn
if yloc[-1] / sep > max_lines*10:
# y-axis scale >> x-axis scale
wn = yloc # one frequency per y-axis tick mark
else:
wn = xloc # one frequency per x-axis tick mark

wn = xloc # one frequency per x-axis tick mark
sep = xloc[1]-xloc[0] # separation between ticks

# Insert additional frequencies to span the y-axis
while np.abs(wn[0]) < ylim[1]:
wn = np.insert(wn, 0, wn[0]-sep)
# Insert additional frequencies to span the y-axis
while np.abs(wn[0]) < yloc[-1]:
wn = np.insert(wn, 0, wn[0]-sep)

# If there are too many values, cut them in half
while len(wn) > 7:
while len(wn) > max_lines:
wn = wn[0:-1:2]

return wn
Expand Down
29 changes: 29 additions & 0 deletions control/tests/rlocus_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@
from numpy.testing import assert_array_almost_equal
import pytest

import control as ct
from control.rlocus import root_locus, _RLClickDispatcher
from control.xferfcn import TransferFunction
from control.statesp import StateSpace
Expand Down Expand Up @@ -74,3 +75,31 @@ def test_root_locus_zoom(self):

assert_array_almost_equal(zoom_x, zoom_x_valid)
assert_array_almost_equal(zoom_y, zoom_y_valid)

def test_rlocus_default_wn(self):
"""Check that default wn calculation works properly"""
#
# System that triggers use of y-axis as basis for wn (for coverage)
#
# This system generates a root locus plot that used to cause the
# creation (and subsequent deletion) of a large number of natural
# frequency contours within the `_default_wn` function in `rlocus.py`.
# This unit test makes sure that is fixed by generating a test case
# that will take a long time to do the calculation (minutes).
#
import scipy as sp
import signal

# Define a system that exhibits this behavior
sys = ct.tf(*sp.signal.zpk2tf(
[-1e-2, 1-1e7j, 1+1e7j], [0, -1e7j, 1e7j], 1))

# Set up a timer to catch execution time
def signal_handler(signum, frame):
raise Exception("rlocus took too long to complete")
signal.signal(signal.SIGALRM, signal_handler)

# Run the command and reset the alarm
signal.alarm(2) # 2 second timeout
ct.root_locus(sys)
signal.alarm(0) # reset the alarm