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Fix margin() documentation to address issue #195 #198

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Merged
merged 3 commits into from
Jul 2, 2018
Merged

Fix margin() documentation to address issue #195 #198

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2646ead
Fix margin() documentation to address issue #195
murrayrm Feb 24, 2018
9fd6ae7
DOC: remove extraneous ininfo from docstring (margin always returns s…
murrayrm Feb 24, 2018
1593391
Clarify comments on margin and stability_margins functions
repagh Jul 2, 2018
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32 changes: 18 additions & 14 deletions control/margins.py
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Original file line number Diff line number Diff line change
Expand Up @@ -108,12 +108,12 @@ def stability_margins(sysdata, returnall=False, epsw=0.0):
Linear SISO system
mag, phase, omega : sequence of array_like
Arrays of magnitudes (absolute values, not dB), phases (degrees),
and corresponding frequencies. Crossover frequencies returned are
and corresponding frequencies. Crossover frequencies returned are
in the same units as those in `omega` (e.g., rad/sec or Hz).
returnall: bool, optional
If true, return all margins found. If false (default), return only the
minimum stability margins. For frequency data or FRD systems, only one
margin is found and returned.
If true, return all margins found. If False (default), return only the
minimum stability margins. For frequency data or FRD systems, only
margins in the given frequency region can be found and returned.
epsw: float, optional
Frequencies below this value (default 0.0) are considered static gain,
and not returned as margin.
Expand All @@ -127,11 +127,11 @@ def stability_margins(sysdata, returnall=False, epsw=0.0):
sm: float or array_like
Stability margin, the minimum distance from the Nyquist plot to -1
wg: float or array_like
Gain margin crossover frequency (where phase crosses -180 degrees)
Frequency for gain margin (at phase crossover, phase = -180 degrees)
wp: float or array_like
Phase margin crossover frequency (where gain crosses 0 dB)
Frequency for phase margin (at gain crossover, gain = 0 dB)
ws: float or array_like
Stability margin frequency (where Nyquist plot is closest to -1)
Frequency for stability margin (complex gain closest to -1)
"""

try:
Expand Down Expand Up @@ -340,18 +340,22 @@ def margin(*args):
Gain margin
pm : float
Phase margin (in degrees)
Wcg : float
Gain crossover frequency (corresponding to phase margin)
Wcp : float
Phase crossover frequency (corresponding to gain margin) (in rad/sec)
wg: float
Frequency for gain margin (at phase crossover, phase = -180 degrees)
wp: float
Frequency for phase margin (at gain crossover, gain = 0 dB)

Margins are of SISO open-loop. If more than one crossover frequency is
detected, returns the lowest corresponding margin.
Margins are calculated for a SISO open-loop system.

If there is more than one gain crossover, the one at the smallest
margin (deviation from gain=0dB), in absolute sense, is
returned. Likewise the smallest phase margin (in absolute sense)
is returned.

Examples
--------
>>> sys = tf(1, [1, 2, 1, 0])
>>> gm, pm, Wcg, Wcp = margin(sys)
>>> gm, pm, wg, wp = margin(sys)

"""
if len(args) == 1:
Expand Down