diff --git a/control/freqplot.py b/control/freqplot.py
index 448814a55..5a03694db 100644
--- a/control/freqplot.py
+++ b/control/freqplot.py
@@ -78,6 +78,7 @@
'bode.deg': True, # Plot phase in degrees
'bode.Hz': False, # Plot frequency in Hertz
'bode.grid': True, # Turn on grid for gain and phase
+ 'bode.wrap_phase': False, # Wrap the phase plot at a given value
}
@@ -131,7 +132,19 @@ def bode_plot(syslist, omega=None,
grid : bool
If True, plot grid lines on gain and phase plots. Default is set by
`config.defaults['bode.grid']`.
-
+ initial_phase : float
+ Set the reference phase to use for the lowest frequency. If set, the
+ initial phase of the Bode plot will be set to the value closest to the
+ value specified. Units are in either degrees or radians, depending on
+ the `deg` parameter. Default is -180 if wrap_phase is False, 0 if
+ wrap_phase is True.
+ wrap_phase : bool or float
+ If wrap_phase is `False`, then the phase will be unwrapped so that it
+ is continuously increasing or decreasing. If wrap_phase is `True` the
+ phase will be restricted to the range [-180, 180) (or [:math:`-\\pi`,
+ :math:`\\pi`) radians). If `wrap_phase` is specified as a float, the
+ phase will be offset by 360 degrees if it falls below the specified
+ value. Default to `False`, set by config.defaults['bode.wrap_phase'].
The default values for Bode plot configuration parameters can be reset
using the `config.defaults` dictionary, with module name 'bode'.
@@ -171,6 +184,10 @@ def bode_plot(syslist, omega=None,
grid = config._get_param('bode', 'grid', kwargs, _bode_defaults, pop=True)
plot = config._get_param('bode', 'grid', plot, True)
margins = config._get_param('bode', 'margins', margins, False)
+ wrap_phase = config._get_param(
+ 'bode', 'wrap_phase', kwargs, _bode_defaults, pop=True)
+ initial_phase = config._get_param(
+ 'bode', 'initial_phase', kwargs, None, pop=True)
# If argument was a singleton, turn it into a list
if not getattr(syslist, '__iter__', False):
@@ -209,11 +226,47 @@ def bode_plot(syslist, omega=None,
# TODO: What distance to the Nyquist frequency is appropriate?
else:
nyquistfrq = None
+
# Get the magnitude and phase of the system
mag_tmp, phase_tmp, omega_sys = sys.freqresp(omega_sys)
mag = np.atleast_1d(np.squeeze(mag_tmp))
phase = np.atleast_1d(np.squeeze(phase_tmp))
- phase = unwrap(phase)
+
+ #
+ # Post-process the phase to handle initial value and wrapping
+ #
+
+ if initial_phase is None:
+ # Start phase in the range 0 to -360 w/ initial phase = -180
+ # If wrap_phase is true, use 0 instead (phase \in (-pi, pi])
+ initial_phase = -math.pi if wrap_phase is not True else 0
+ elif isinstance(initial_phase, (int, float)):
+ # Allow the user to override the default calculation
+ if deg:
+ initial_phase = initial_phase/180. * math.pi
+ else:
+ raise ValueError("initial_phase must be a number.")
+
+ # Shift the phase if needed
+ if abs(phase[0] - initial_phase) > math.pi:
+ phase -= 2*math.pi * \
+ round((phase[0] - initial_phase) / (2*math.pi))
+
+ # Phase wrapping
+ if wrap_phase is False:
+ phase = unwrap(phase) # unwrap the phase
+ elif wrap_phase is True:
+ pass # default calculation OK
+ elif isinstance(wrap_phase, (int, float)):
+ phase = unwrap(phase) # unwrap the phase first
+ if deg:
+ wrap_phase *= math.pi/180.
+
+ # Shift the phase if it is below the wrap_phase
+ phase += 2*math.pi * np.maximum(
+ 0, np.ceil((wrap_phase - phase)/(2*math.pi)))
+ else:
+ raise ValueError("wrap_phase must be bool or float.")
mags.append(mag)
phases.append(phase)
@@ -270,7 +323,9 @@ def bode_plot(syslist, omega=None,
label='control-bode-phase',
sharex=ax_mag)
+ #
# Magnitude plot
+ #
if dB:
pltline = ax_mag.semilogx(omega_plot, 20 * np.log10(mag),
*args, **kwargs)
@@ -285,19 +340,22 @@ def bode_plot(syslist, omega=None,
ax_mag.grid(grid and not margins, which='both')
ax_mag.set_ylabel("Magnitude (dB)" if dB else "Magnitude")
+ #
# Phase plot
- if deg:
- phase_plot = phase * 180. / math.pi
- else:
- phase_plot = phase
+ #
+ phase_plot = phase * 180. / math.pi if deg else phase
+
+ # Plot the data
ax_phase.semilogx(omega_plot, phase_plot, *args, **kwargs)
# Show the phase and gain margins in the plot
if margins:
+ # Compute stability margins for the system
margin = stability_margins(sys)
- gm, pm, Wcg, Wcp = \
- margin[0], margin[1], margin[3], margin[4]
- # TODO: add some documentation describing why this is here
+ gm, pm, Wcg, Wcp = (margin[i] for i in (0, 1, 3, 4))
+
+ # Figure out sign of the phase at the first gain crossing
+ # (needed if phase_wrap is True)
phase_at_cp = phases[0][(np.abs(omegas[0] - Wcp)).argmin()]
if phase_at_cp >= 0.:
phase_limit = 180.
@@ -307,6 +365,7 @@ def bode_plot(syslist, omega=None,
if Hz:
Wcg, Wcp = Wcg/(2*math.pi), Wcp/(2*math.pi)
+ # Draw lines at gain and phase limits
ax_mag.axhline(y=0 if dB else 1, color='k', linestyle=':',
zorder=-20)
ax_phase.axhline(y=phase_limit if deg else
@@ -315,6 +374,7 @@ def bode_plot(syslist, omega=None,
mag_ylim = ax_mag.get_ylim()
phase_ylim = ax_phase.get_ylim()
+ # Annotate the phase margin (if it exists)
if pm != float('inf') and Wcp != float('nan'):
if dB:
ax_mag.semilogx(
@@ -327,7 +387,7 @@ def bode_plot(syslist, omega=None,
if deg:
ax_phase.semilogx(
- [Wcp, Wcp], [1e5, phase_limit+pm],
+ [Wcp, Wcp], [1e5, phase_limit + pm],
color='k', linestyle=':', zorder=-20)
ax_phase.semilogx(
[Wcp, Wcp], [phase_limit + pm, phase_limit],
@@ -343,6 +403,7 @@ def bode_plot(syslist, omega=None,
math.radians(phase_limit)],
color='k', zorder=-20)
+ # Annotate the gain margin (if it exists)
if gm != float('inf') and Wcg != float('nan'):
if dB:
ax_mag.semilogx(
@@ -360,11 +421,11 @@ def bode_plot(syslist, omega=None,
if deg:
ax_phase.semilogx(
- [Wcg, Wcg], [1e-8, phase_limit],
+ [Wcg, Wcg], [0, phase_limit],
color='k', linestyle=':', zorder=-20)
else:
ax_phase.semilogx(
- [Wcg, Wcg], [1e-8, math.radians(phase_limit)],
+ [Wcg, Wcg], [0, math.radians(phase_limit)],
color='k', linestyle=':', zorder=-20)
ax_mag.set_ylim(mag_ylim)
diff --git a/control/tests/freqresp_test.py b/control/tests/freqresp_test.py
index 29c67d9af..111d4296c 100644
--- a/control/tests/freqresp_test.py
+++ b/control/tests/freqresp_test.py
@@ -9,6 +9,7 @@
import matplotlib.pyplot as plt
import numpy as np
from numpy.testing import assert_allclose
+import math
import pytest
import control as ctrl
@@ -173,7 +174,7 @@ def test_bode_margin(dB, maginfty1, maginfty2, gminv,
rtol=1e-5)
phase_to_infinity = (np.array([Wcg, Wcg]),
- np.array([1e-8, p0]))
+ np.array([0, p0]))
assert_allclose(phase_to_infinity, allaxes[1].lines[4].get_data(),
rtol=1e-5)
@@ -271,3 +272,67 @@ def test_options(editsdefaults):
# Make sure we got the right number of points
assert numpoints1 != numpoints3
assert numpoints3 == 13
+
+@pytest.mark.parametrize(
+ "TF, initial_phase, default_phase, expected_phase",
+ [pytest.param(ctrl.tf([1], [1, 0]),
+ None, -math.pi/2, -math.pi/2, id="order1, default"),
+ pytest.param(ctrl.tf([1], [1, 0]),
+ 180, -math.pi/2, 3*math.pi/2, id="order1, 180"),
+ pytest.param(ctrl.tf([1], [1, 0, 0]),
+ None, -math.pi, -math.pi, id="order2, default"),
+ pytest.param(ctrl.tf([1], [1, 0, 0]),
+ 180, -math.pi, math.pi, id="order2, 180"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0]),
+ None, -3*math.pi/2, -3*math.pi/2, id="order2, default"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0]),
+ 180, -3*math.pi/2, math.pi/2, id="order2, 180"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0]),
+ None, 0, 0, id="order4, default"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0]),
+ 180, 0, 0, id="order4, 180"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0]),
+ -360, 0, -2*math.pi, id="order4, -360"),
+ ])
+def test_initial_phase(TF, initial_phase, default_phase, expected_phase):
+ # Check initial phase of standard transfer functions
+ mag, phase, omega = ctrl.bode(TF)
+ assert(abs(phase[0] - default_phase) < 0.1)
+
+ # Now reset the initial phase to +180 and see if things work
+ mag, phase, omega = ctrl.bode(TF, initial_phase=initial_phase)
+ assert(abs(phase[0] - expected_phase) < 0.1)
+
+ # Make sure everything works in rad/sec as well
+ if initial_phase:
+ plt.clf() # clear previous figure (speeds things up)
+ mag, phase, omega = ctrl.bode(
+ TF, initial_phase=initial_phase/180. * math.pi, deg=False)
+ assert(abs(phase[0] - expected_phase) < 0.1)
+
+
+@pytest.mark.parametrize(
+ "TF, wrap_phase, min_phase, max_phase",
+ [pytest.param(ctrl.tf([1], [1, 0]),
+ None, -math.pi/2, 0, id="order1, default"),
+ pytest.param(ctrl.tf([1], [1, 0]),
+ True, -math.pi, math.pi, id="order1, True"),
+ pytest.param(ctrl.tf([1], [1, 0]),
+ -270, -3*math.pi/2, math.pi/2, id="order1, -270"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0]),
+ None, -3*math.pi/2, 0, id="order3, default"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0]),
+ True, -math.pi, math.pi, id="order3, True"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0]),
+ -270, -3*math.pi/2, math.pi/2, id="order3, -270"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0, 0]),
+ True, -3*math.pi/2, 0, id="order5, default"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0, 0]),
+ True, -math.pi, math.pi, id="order5, True"),
+ pytest.param(ctrl.tf([1], [1, 0, 0, 0, 0, 0]),
+ -270, -3*math.pi/2, math.pi/2, id="order5, -270"),
+ ])
+def test_phase_wrap(TF, wrap_phase, min_phase, max_phase):
+ mag, phase, omega = ctrl.bode(TF, wrap_phase=wrap_phase)
+ assert(min(phase) >= min_phase)
+ assert(max(phase) <= max_phase)
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