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Commitbe59f62

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Merge pull request#264 from don4get/refactor/cleaning-nichols
Clean up nichols.py
2 parents5ff1184 +9179e89 commitbe59f62

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‎control/nichols.py

Lines changed: 34 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,13 @@
1+
"""nichols.py
2+
3+
Functions for plotting Black-Nichols charts.
4+
5+
Routines in this module:
6+
7+
nichols.nichols_plot aliased as nichols.nichols
8+
nichols.nichols_grid
9+
"""
10+
111
# nichols.py - Nichols plot
212
#
313
# Contributed by Allan McInnes <Allan.McInnes@canterbury.ac.nz>
@@ -45,17 +55,17 @@
4555
from .ctrlutilimportunwrap
4656
from .freqplotimportdefault_frequency_range
4757

48-
__all__= ['nichols_plot','nichols']
58+
__all__= ['nichols_plot','nichols','nichols_grid']
59+
4960

50-
# Nichols plot
51-
defnichols_plot(syslist,omega=None,grid=True):
61+
defnichols_plot(sys_list,omega=None,grid=True):
5262
"""Nichols plot for a system
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5464
Plots a Nichols plot for the system over a (optional) frequency range.
5565
5666
Parameters
5767
----------
58-
syslist : list of LTI, or LTI
68+
sys_list : list of LTI, or LTI
5969
List of linear input/output systems (single system is OK)
6070
omega : array_like
6171
Range of frequencies (list or bounds) in rad/sec
@@ -68,14 +78,14 @@ def nichols_plot(syslist, omega=None, grid=True):
6878
"""
6979

7080
# If argument was a singleton, turn it into a list
71-
if(notgetattr(syslist,'__iter__',False)):
72-
syslist= (syslist,)
81+
ifnotgetattr(sys_list,'__iter__',False):
82+
sys_list= (sys_list,)
7383

7484
# Select a default range if none is provided
7585
ifomegaisNone:
76-
omega=default_frequency_range(syslist)
86+
omega=default_frequency_range(sys_list)
7787

78-
forsysinsyslist:
88+
forsysinsys_list:
7989
# Get the magnitude and phase of the system
8090
mag_tmp,phase_tmp,omega=sys.freqresp(omega)
8191
mag=np.squeeze(mag_tmp)
@@ -100,9 +110,8 @@ def nichols_plot(syslist, omega=None, grid=True):
100110
ifgrid:
101111
nichols_grid()
102112

103-
# Nichols grid
104-
#! TODO: Consider making linestyle configurable
105-
defnichols_grid(cl_mags=None,cl_phases=None):
113+
114+
defnichols_grid(cl_mags=None,cl_phases=None,line_style='dotted'):
106115
"""Nichols chart grid
107116
108117
Plots a Nichols chart grid on the current axis, or creates a new chart
@@ -116,6 +125,8 @@ def nichols_grid(cl_mags=None, cl_phases=None):
116125
cl_phases : array-like (degrees), optional
117126
Array of closed-loop phases defining the iso-phase lines on a custom
118127
Nichols chart. Must be in the range -360 < cl_phases < 0
128+
line_style : string, optional
129+
.. seealso:: https://matplotlib.org/gallery/lines_bars_and_markers/linestyles.html
119130
120131
Returns
121132
-------
@@ -137,12 +148,12 @@ def nichols_grid(cl_mags=None, cl_phases=None):
137148
# The key set of magnitudes are always generated, since this
138149
# guarantees a recognizable Nichols chart grid.
139150
key_cl_mags=np.array([-40.0,-20.0,-12.0,-6.0,-3.0,-1.0,-0.5,0.0,
140-
0.25,0.5,1.0,3.0,6.0,12.0])
151+
0.25,0.5,1.0,3.0,6.0,12.0])
141152
# Extend the range of magnitudes if necessary. The extended arange
142153
# will end up empty if no extension is required. Assumes that closed-loop
143154
# magnitudes are approximately aligned with open-loop magnitudes beyond
144155
# the value of np.min(key_cl_mags)
145-
cl_mag_step=-20.0# dB
156+
cl_mag_step=-20.0# dB
146157
extended_cl_mags=np.arange(np.min(key_cl_mags),
147158
ol_mag_min+cl_mag_step,cl_mag_step)
148159
cl_mags=np.concatenate((extended_cl_mags,key_cl_mags))
@@ -163,12 +174,12 @@ def nichols_grid(cl_mags=None, cl_phases=None):
163174
# Find the M-contours
164175
m=m_circles(cl_mags,phase_min=np.min(cl_phases),phase_max=np.max(cl_phases))
165176
m_mag=20*sp.log10(np.abs(m))
166-
m_phase=sp.mod(sp.degrees(sp.angle(m)),-360.0)# Unwrap
177+
m_phase=sp.mod(sp.degrees(sp.angle(m)),-360.0)# Unwrap
167178

168179
# Find the N-contours
169180
n=n_circles(cl_phases,mag_min=np.min(cl_mags),mag_max=np.max(cl_mags))
170181
n_mag=20*sp.log10(np.abs(n))
171-
n_phase=sp.mod(sp.degrees(sp.angle(n)),-360.0)# Unwrap
182+
n_phase=sp.mod(sp.degrees(sp.angle(n)),-360.0)# Unwrap
172183

173184
# Plot the contours behind other plot elements.
174185
# The "phase offset" is used to produce copies of the chart that cover
@@ -182,10 +193,10 @@ def nichols_grid(cl_mags=None, cl_phases=None):
182193

183194
forphase_offsetinphase_offsets:
184195
# Draw M and N contours
185-
plt.plot(m_phase+phase_offset,m_mag,color='gray',
186-
linestyle='dotted',zorder=0)
187-
plt.plot(n_phase+phase_offset,n_mag,color='gray',
188-
linestyle='dotted',zorder=0)
196+
plt.plot(m_phase+phase_offset,m_mag,color='lightgray',
197+
linestyle=line_style,zorder=0)
198+
plt.plot(n_phase+phase_offset,n_mag,color='lightgray',
199+
linestyle=line_style,zorder=0)
189200

190201
# Add magnitude labels
191202
forx,y,minzip(m_phase[:][-1]+phase_offset,m_mag[:][-1],cl_mags):
@@ -203,7 +214,7 @@ def nichols_grid(cl_mags=None, cl_phases=None):
203214
# generating Nichols plots
204215
#
205216

206-
# Compute contours of a closed-loop transfer function
217+
207218
defclosed_loop_contours(Gcl_mags,Gcl_phases):
208219
"""Contours of the function Gcl = Gol/(1+Gol), where
209220
Gol is an open-loop transfer function, and Gcl is a corresponding
@@ -229,7 +240,7 @@ def closed_loop_contours(Gcl_mags, Gcl_phases):
229240
# Invert Gcl = Gol/(1+Gol) to map the contours into the open-loop space
230241
returnGcl/(1.0-Gcl)
231242

232-
# M-circle
243+
233244
defm_circles(mags,phase_min=-359.75,phase_max=-0.25):
234245
"""Constant-magnitude contours of the function Gcl = Gol/(1+Gol), where
235246
Gol is an open-loop transfer function, and Gcl is a corresponding
@@ -255,7 +266,7 @@ def m_circles(mags, phase_min=-359.75, phase_max=-0.25):
255266
Gcl_mags,Gcl_phases=sp.meshgrid(10.0**(mags/20.0),phases)
256267
returnclosed_loop_contours(Gcl_mags,Gcl_phases)
257268

258-
# N-circle
269+
259270
defn_circles(phases,mag_min=-40.0,mag_max=12.0):
260271
"""Constant-phase contours of the function Gcl = Gol/(1+Gol), where
261272
Gol is an open-loop transfer function, and Gcl is a corresponding
@@ -281,5 +292,6 @@ def n_circles(phases, mag_min=-40.0, mag_max=12.0):
281292
Gcl_phases,Gcl_mags=sp.meshgrid(sp.radians(phases),mags)
282293
returnclosed_loop_contours(Gcl_mags,Gcl_phases)
283294

295+
284296
# Function aliases
285297
nichols=nichols_plot

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