diff --git a/control/freqplot.py b/control/freqplot.py
index c53e83f31..a71d44cce 100644
--- a/control/freqplot.py
+++ b/control/freqplot.py
@@ -171,22 +171,47 @@ def bode_plot(syslist, omega=None, dB=None, Hz=None, deg=None,
#! TODO: Not current implemented; just use subplot for now
if (Plot):
+ # Set up the axes with labels so that multiple calls to
+ # bode_plot will superimpose the data. This was implicit
+ # before matplotlib 2.1, but changed after that (See
+ # https://github.com/matplotlib/matplotlib/issues/9024).
+ # The code below should work on all cases.
+
+ # Get the current figure
+ fig = plt.gcf()
+ ax_mag = None
+ ax_phase = None
+
+ # Get the current axes if they already exist
+ for ax in fig.axes:
+ if ax.get_label() == 'control-bode-magnitude':
+ ax_mag = ax
+ elif ax.get_label() == 'control-bode-phase':
+ ax_phase = ax
+
+ # If no axes present, create them from scratch
+ if ax_mag is None or ax_phase is None:
+ plt.clf()
+ ax_mag = plt.subplot(211, label = 'control-bode-magnitude')
+ ax_phase = plt.subplot(212, label = 'control-bode-phase',
+ sharex=ax_mag)
+
# Magnitude plot
- ax_mag = plt.subplot(211);
if dB:
- pltline = ax_mag.semilogx(omega_plot, 20 * np.log10(mag), *args, **kwargs)
+ pltline = ax_mag.semilogx(omega_plot, 20 * np.log10(mag),
+ *args, **kwargs)
else:
pltline = ax_mag.loglog(omega_plot, mag, *args, **kwargs)
if nyquistfrq_plot:
- ax_mag.axvline(nyquistfrq_plot, color=pltline[0].get_color())
+ ax_mag.axvline(nyquistfrq_plot,
+ color=pltline[0].get_color())
# Add a grid to the plot + labeling
ax_mag.grid(True, which='both')
ax_mag.set_ylabel("Magnitude (dB)" if dB else "Magnitude")
# Phase plot
- ax_phase = plt.subplot(212, sharex=ax_mag);
if deg:
phase_plot = phase * 180. / math.pi
else:
@@ -353,28 +378,50 @@ def gangof4_plot(P, C, omega=None):
L = P * C;
S = feedback(1, L);
T = L * S;
-
+
+ # Set up the axes with labels so that multiple calls to
+ # gangof4_plot will superimpose the data. See details in bode_plot.
+ plot_axes = {'t' : None, 's' : None, 'ps' : None, 'cs' : None}
+ for ax in plt.gcf().axes:
+ label = ax.get_label()
+ if label.startswith('control-gangof4-'):
+ key = label[len('control-gangof4-'):]
+ if key not in plot_axes:
+ raise RuntimeError("unknown gangof4 axis type '{}'".format(label))
+ plot_axes[key] = ax
+
+ # if any of the axes are missing, start from scratch
+ if any((ax is None for ax in plot_axes.values())):
+ plt.clf()
+ plot_axes = {'t' : plt.subplot(221,label='control-gangof4-t'),
+ 'ps' : plt.subplot(222,label='control-gangof4-ps'),
+ 'cs' : plt.subplot(223,label='control-gangof4-cs'),
+ 's' : plt.subplot(224,label='control-gangof4-s')}
+
+ #
# Plot the four sensitivity functions
+ #
+
#! TODO: Need to add in the mag = 1 lines
mag_tmp, phase_tmp, omega = T.freqresp(omega);
mag = np.squeeze(mag_tmp)
phase = np.squeeze(phase_tmp)
- plt.subplot(221); plt.loglog(omega, mag);
+ plot_axes['t'].loglog(omega, mag);
mag_tmp, phase_tmp, omega = (P * S).freqresp(omega);
mag = np.squeeze(mag_tmp)
phase = np.squeeze(phase_tmp)
- plt.subplot(222); plt.loglog(omega, mag);
+ plot_axes['ps'].loglog(omega, mag);
mag_tmp, phase_tmp, omega = (C * S).freqresp(omega);
mag = np.squeeze(mag_tmp)
phase = np.squeeze(phase_tmp)
- plt.subplot(223); plt.loglog(omega, mag);
+ plot_axes['cs'].loglog(omega, mag);
mag_tmp, phase_tmp, omega = S.freqresp(omega);
mag = np.squeeze(mag_tmp)
phase = np.squeeze(phase_tmp)
- plt.subplot(224); plt.loglog(omega, mag);
+ plot_axes['s'].loglog(omega, mag);
#
# Utility functions
diff --git a/control/statesp.py b/control/statesp.py
index c71f5cd49..bff14d241 100644
--- a/control/statesp.py
+++ b/control/statesp.py
@@ -1078,18 +1078,18 @@ def ss(*args):
output equations:
.. math::
- \dot x = A \cdot x + B \cdot u
+ \\dot x = A \\cdot x + B \\cdot u
- y = C \cdot x + D \cdot u
+ y = C \\cdot x + D \\cdot u
``ss(A, B, C, D, dt)``
Create a discrete-time state space system from the matrices of
its state and output equations:
.. math::
- x[k+1] = A \cdot x[k] + B \cdot u[k]
+ x[k+1] = A \\cdot x[k] + B \\cdot u[k]
- y[k] = C \cdot x[k] + D \cdot u[ki]
+ y[k] = C \\cdot x[k] + D \\cdot u[ki]
The matrices can be given as *array like* data types or strings.
Everything that the constructor of :class:`numpy.matrix` accepts is
diff --git a/control/tests/freqresp_test.py b/control/tests/freqresp_test.py
index aa3670d8c..9e8dd44ce 100644
--- a/control/tests/freqresp_test.py
+++ b/control/tests/freqresp_test.py
@@ -8,6 +8,7 @@
import unittest
import numpy as np
+import control as ctrl
from control.statesp import StateSpace
from control.matlab import ss, tf, bode
from control.exception import slycot_check
@@ -34,6 +35,50 @@ def test_siso(self):
systf = tf(sys)
bode(systf)
+ def test_superimpose(self):
+ # Test to make sure that multiple calls to plots superimpose their
+ # data on the same axes unless told to do otherwise
+
+ # Generate two plots in a row; should be on the same axes
+ plt.figure(1); plt.clf()
+ ctrl.bode_plot(ctrl.tf([1], [1,2,1]))
+ ctrl.bode_plot(ctrl.tf([5], [1, 1]))
+
+ # Check to make sure there are two axes and that each axes has two lines
+ assert len(plt.gcf().axes) == 2
+ for ax in plt.gcf().axes:
+ # Make sure there are 2 lines in each subplot
+ assert len(ax.get_lines()) == 2
+
+ # Generate two plots as a list; should be on the same axes
+ plt.figure(2); plt.clf();
+ ctrl.bode_plot([ctrl.tf([1], [1,2,1]), ctrl.tf([5], [1, 1])])
+
+ # Check to make sure there are two axes and that each axes has two lines
+ assert len(plt.gcf().axes) == 2
+ for ax in plt.gcf().axes:
+ # Make sure there are 2 lines in each subplot
+ assert len(ax.get_lines()) == 2
+
+ # Generate two separate plots; only the second should appear
+ plt.figure(3); plt.clf();
+ ctrl.bode_plot(ctrl.tf([1], [1,2,1]))
+ plt.clf()
+ ctrl.bode_plot(ctrl.tf([5], [1, 1]))
+
+ # Check to make sure there are two axes and that each axes has one line
+ assert len(plt.gcf().axes) == 2
+ for ax in plt.gcf().axes:
+ # Make sure there is only 1 line in the subplot
+ assert len(ax.get_lines()) == 1
+
+ # Now add a line to the magnitude plot and make sure if is there
+ for ax in plt.gcf().axes:
+ if ax.get_label() == 'control-bode-magnitude':
+ break
+ ax.semilogx([1e-2, 1e1], 20 * np.log10([1, 1]), 'k-')
+ assert len(ax.get_lines()) == 2
+
def test_doubleint(self):
# 30 May 2016, RMM: added to replicate typecast bug in freqresp.py
A = np.matrix('0, 1; 0, 0');
diff --git a/doc/control.rst b/doc/control.rst
index ec35f6626..c12936f42 100644
--- a/doc/control.rst
+++ b/doc/control.rst
@@ -44,6 +44,15 @@ Frequency domain plotting
gangof4_plot
nichols_plot
+Note: For plotting commands that create multiple axes on the same plot, the
+individual axes can be retrieved using the axes label (retrieved using the
+`get_label` method for the matplotliib axes object). The following labels
+are currently defined:
+
+* Bode plots: `control-bode-magnitude`, `control-bode-phase`
+* Gang of 4 plots: `control-gangof4-s`, `control-gangof4-cs`,
+ `control-gangof4-ps`, `control-gangof4-t`
+
Time domain simulation
======================
diff --git a/examples/pvtol-nested.py b/examples/pvtol-nested.py
index 934f4b5ca..e02d86352 100644
--- a/examples/pvtol-nested.py
+++ b/examples/pvtol-nested.py
@@ -81,26 +81,45 @@
T = feedback(L, 1);
# Compute stability margins
-#! Not yet implemented
-# (gm, pm, wgc, wpc) = margin(L);
+(gm, pm, wgc, wpc) = margin(L);
+print("Gain margin: %g at %g" % (gm, wgc))
+print("Phase margin: %g at %g" % (pm, wpc))
-#! TODO: this figure has something wrong; axis limits mismatch
figure(6); clf;
-bode(L);
+bode(L, logspace(-4, 3));
-# Add crossover line
-subplot(211); hold(True);
-loglog([1e-4, 1e3], [1, 1], 'k-')
+# Add crossover line to the magnitude plot
+#
+# Note: in matplotlib before v2.1, the following code worked:
+#
+# subplot(211); hold(True);
+# loglog([1e-4, 1e3], [1, 1], 'k-')
+#
+# In later versions of matplotlib the call to subplot will clear the
+# axes and so we have to extract the axes that we want to use by hand.
+# In addition, hold() is deprecated so we no longer require it.
+#
+for ax in gcf().axes:
+ if ax.get_label() == 'control-bode-magnitude':
+ break
+ax.semilogx([1e-4, 1e3], 20 * np.log10([1, 1]), 'k-')
+#
# Replot phase starting at -90 degrees
-bode(L, logspace(-4, 3));
+#
+# Get the phase plot axes
+for ax in gcf().axes:
+ if ax.get_label() == 'control-bode-phase':
+ break
+
+# Recreate the frequency response and shift the phase
(mag, phase, w) = freqresp(L, logspace(-4, 3));
phase = phase - 360;
-subplot(212);
-semilogx([1e-4, 1e3], [-180, -180], 'k-')
-hold(True);
-semilogx(w, np.squeeze(phase), 'b-')
-axis([1e-4, 1e3, -360, 0]);
+
+# Replot the phase by hand
+ax.semilogx([1e-4, 1e3], [-180, -180], 'k-')
+ax.semilogx(w, np.squeeze(phase), 'b-')
+ax.axis([1e-4, 1e3, -360, 0]);
xlabel('Frequency [deg]'); ylabel('Phase [deg]');
# set(gca, 'YTick', [-360, -270, -180, -90, 0]);
# set(gca, 'XTick', [10^-4, 10^-2, 1, 100]);
@@ -109,7 +128,6 @@
# Nyquist plot for complete design
#
figure(7); clf;
-axis([-700, 5300, -3000, 3000]); hold(True);
nyquist(L, (0.0001, 1000));
axis([-700, 5300, -3000, 3000]);
@@ -118,7 +136,6 @@
# Expanded region
figure(8); clf; subplot(231);
-axis([-10, 5, -20, 20]); hold(True);
nyquist(L);
axis([-10, 5, -20, 20]);
@@ -136,7 +153,7 @@
figure(9);
(Yvec, Tvec) = step(T, linspace(0, 20));
-plot(Tvec.T, Yvec.T); hold(True);
+plot(Tvec.T, Yvec.T);
(Yvec, Tvec) = step(Co*S, linspace(0, 20));
plot(Tvec.T, Yvec.T);
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