@@ -108,12 +108,12 @@ def stability_margins(sysdata, returnall=False, epsw=0.0):
108108 Linear SISO system
109109 mag, phase, omega : sequence of array_like
110110 Arrays of magnitudes (absolute values, not dB), phases (degrees),
111- and corresponding frequencies.
111+ and corresponding frequencies. Crossover frequencies returned are
112112 in the same units as those in `omega` (e.g., rad/sec or Hz).
113113 returnall: bool, optional
114- If true, return all margins found. Iffalse (default), return only the
115- minimum stability margins. one
116- margin is found and returned.
114+ If true, return all margins found. IfFalse (default), return only the
115+ minimum stability margins. For frequency data or FRD systems, only
116+ margins in the given frequency region can be found and returned.
117117 epsw: float, optional
118118 Frequencies below this value (default 0.0) are considered static gain,
119119 and not returned as margin.
@@ -127,11 +127,11 @@ def stability_margins(sysdata, returnall=False, epsw=0.0):
127127 sm: float or array_like
128128 Stability margin, the minimum distance from the Nyquist plot to -1
129129 wg: float or array_like
130- Gain margin crossover frequency (where phasecrosses -180 degrees)
130+ Frequency for gain margin (at phasecrossover, phase = -180 degrees)
131131 wp: float or array_like
132- Phase margin crossover frequency (where gaincrosses 0 dB)
132+ Frequency for phase margin (at gaincrossover, gain = 0 dB)
133133 ws: float or array_like
134- Stability margin frequency (where Nyquist plot is closest to -1)
134+ Frequency for stability margin (complex gain closest to -1)
135135 """
136136
137137try :
@@ -340,18 +340,22 @@ def margin(*args):
340340 Gain margin
341341 pm : float
342342 Phase margin (in degrees)
343- Wcg : float
344- Gain crossover frequency (corresponding to phasemargin )
345- Wcp : float
346- Phase crossover frequency (corresponding to gainmargin) (in rad/sec )
343+ wg : float
344+ Frequency for gain margin (at phase crossover, phase= -180 degrees )
345+ wp : float
346+ Frequency for phase margin (at gain crossover, gain= 0 dB )
347347
348- Margins are of SISO open-loop. If more than one crossover frequency is
349- detected, returns the lowest corresponding margin.
348+ Margins are calculated for a SISO open-loop system.
349+
350+ If there is more than one gain crossover, the one at the smallest
351+ margin (deviation from gain=0dB), in absolute sense, is
352+ returned. Likewise the smallest phase margin (in absolute sense)
353+ is returned.
350354
351355 Examples
352356 --------
353357 >>> sys = tf(1, [1, 2, 1, 0])
354- >>> gm, pm,Wcg, Wcp = margin(sys)
358+ >>> gm, pm,wg, wp = margin(sys)
355359
356360 """
357361if len (args )== 1 :