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bode_utils.py
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bode_utils.py
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from scipy import log10, angle, squeeze, r_, where
import matplotlib
import numpy as np
from numpy import pi
import matplotlib.ticker
from matplotlib.ticker import MultipleLocator, FormatStrFormatter
def unwrap_deg(phase):
phaser = phase*pi/180
phaseru = np.unwrap(phaser)
phase_uw = phaseru*180/pi
return phase_uw
def find_dB_mag_and_phase(Gjw):
dB_mag = 20.0*log10(abs(Gjw))
phase = angle(Gjw,1)
return dB_mag, phase
def _get_fig(fig=None, fignum=1, figsize=None):
if fig is None:
import matplotlib.pyplot as plt
fig = plt.figure(fignum, figsize=figsize)
return fig
def mygrid(ax):
ax.grid(1, which="both",ls=":", color='0.75')
def set_log_ticks(ax,nullx=False):
locmaj = matplotlib.ticker.LogLocator(base=10,numticks=12)
ax.xaxis.set_major_locator(locmaj)
if nullx:
ax.xaxis.set_major_formatter(matplotlib.ticker.NullFormatter())
mysubs = np.arange(0.1,0.99,0.1)
locmin = matplotlib.ticker.LogLocator(base=10.0,subs=mysubs,numticks=12)
ax.xaxis.set_minor_locator(locmin)
ax.xaxis.set_minor_formatter(matplotlib.ticker.NullFormatter())
def set_db_ticks(ax, db):
dbmin = db.min()
dbmax = db.max()
# aim for less than 6 ticks in muliples of 10, 20, 40 , ...
myspan = dbmax-dbmin
maxticks = 6
ticklist = [10,20,40,60,80]
N = None
for tick in ticklist:
if myspan/tick < maxticks:
N = tick
break
if N is None:
N = 100
majorLocator = MultipleLocator(N)
majorFormatter = FormatStrFormatter('%d')
ax.yaxis.set_major_locator(majorLocator)
ax.yaxis.set_major_formatter(majorFormatter)
def set_phase_ticks(ax, phase):
phmin = phase.min()
phmax = phase.max()
# if 4 or 5 multiples of 45 is enough, use 45 as the base
mul45 = (phmax-phmin)/45
if mul45 < 6:
N = 45
elif mul45 < 12:
N = 90
else:
N = 180
majorLocator = MultipleLocator(N)
majorFormatter = FormatStrFormatter('%d')
ax.yaxis.set_major_locator(majorLocator)
ax.yaxis.set_major_formatter(majorFormatter)
def bode_plot(freq, dB_mag, phase, fig=None, fignum=1, clear=True, xlim=None, \
label=None, fmt='-', grid=True, figsize=None, unwrap=False, \
**kwargs):
"""This function plots a very nice Bode plot. freq is a vector in
Hz. dB_mag and phase are vectors with the same length as freq."""
fig = _get_fig(fig, fignum, figsize=figsize)
if clear:
fig.clf()
if len(fig.axes) > 1:
ax = fig.axes[0]
else:
ax = fig.add_subplot(211)
if unwrap:
phase = unwrap_deg(phase)
ax.semilogx(freq, dB_mag, fmt, label=label, **kwargs)
ax.set_ylabel('dB Mag.')
set_log_ticks(ax,nullx=True)
set_db_ticks(ax, dB_mag)
if grid:
mygrid(ax)
#ax.grid(1)
if xlim:
ax.set_xlim(xlim)
if len(fig.axes) > 1:
ax2 = fig.axes[1]
else:
ax2 = fig.add_subplot(212)
ax2.semilogx(freq, phase, fmt, label=label, **kwargs)
ax2.set_ylabel('Phase (deg.)')
ax2.set_xlabel('Freq. (Hz)')
set_log_ticks(ax2)
set_phase_ticks(ax2, phase)
if grid:
#ax2.grid(1)
mygrid(ax2)
if xlim:
ax2.set_xlim(xlim)
def bode_plot2(freq, Gjw, *args, **kwargs):
"""calculate dB_mag and phase from Gjw and then plot a Bode plot
using the bode_plot function, passing in
bode_plot(freq,dB_mag,phase,*args,**kwargs)."""
dB_mag, phase = find_dB_mag_and_phase(Gjw)
bode_plot(freq,dB_mag,phase,*args,**kwargs)
return dB_mag, phase
def bode_plot3(freq, inst, *args, **kwargs):
"""call bode_plot after extracting dBmag and phase from inst. In
theory, any instance that has a dBmag and phase property would
work, but this was created to make it easy to pass in an rwkbode
instance to bode_plot."""
if callable(inst.dBmag):
dB_mag = inst.dBmag()
else:
dB_mag = inst.dBmag
phase = inst.phase
bode_plot(freq,dB_mag,phase,*args,**kwargs)
return dB_mag, phase
def calc_db_mag_and_phase(Gjw, unwrap=False):
dB = 20.0*log10(abs(Gjw))
phase = angle(Gjw, 1)
if unwrap:
phase = unwrap_deg(phase)
return dB, phase
def bode_plot_from_complex(freq, Gjw, fignum=1, clear=False, unwrap=False, \
**kwargs):
dB, phase = calc_db_mag_and_phase(Gjw, unwrap=unwrap)
bode_plot(freq, dB, phase, fignum=fignum, clear=clear, **kwargs)
def crossover_freq(db, freq):
#find where the current db value is greater than 0 and the next one is not
t1=squeeze(db > 0.0)#vector of True and False elements for db > 0.0
t2=r_[t1[1:],t1[0]]#vector t1 shifted by 1 index
t3=(t1 & ~t2)#current value is > 0.0 and the next is not
ind = t3.argmax()
return freq[ind], ind