I am trying to do the Nyquist plot of a function in python, in jupiter notebook. When i try to use the function control.nyquist_plot, used to generate the plot, pyton gives me an error in one of the libraries files. It draws only a part of the nyquist diagram before this error happens.
I also tried to use the same code others were using, to be sure it is not a syntax error, but i get the same error with files that are working for other people.
this is my code:
import numpy as np
import matplotlib.pyplot as plt
import control
sys = control.tf([0, 0, 10], [1, 3, 2])
fig = plt.figure(figsize=(10, 5))
control.nyquist_plot(sys);
And this is the error i get:
ValueError Traceback (most recent call last)
Cell In\[3\], line 4
1 sys = control.tf(\[0, 0, 10\], \[1, 3, 2\])
3 fig = plt.figure(figsize=(10, 5))
\----\> 4 control.nyquist_plot(sys);
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\control\\freqplot.py:1024, in nyquist_plot(syslist, omega, plot, omega_limits, omega_num, label_freq, color, return_contour, warn_encirclements, warn_nyquist, \*\*kwargs)
1022 x_scl = np.ma.masked_where(scale_mask, resp.real)
1023 y_scl = np.ma.masked_where(scale_mask, resp.imag)
\-\> 1024 plt.plot(
1025 x_scl \* (1 + curve_offset), y_scl \* (1 + curve_offset),
1026 primary_style\[1\], color=c, \*\*kwargs)
1028 # Plot the primary curve (invisible) for setting arrows
1029 x, y = resp.real.copy(), resp.imag.copy()
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\pyplot.py:2785, in plot(scalex, scaley, data, \*args, \*\*kwargs)
2783 @\_copy_docstring_and_deprecators(Axes.plot)
2784 def plot(\*args, scalex=True, scaley=True, data=None, \*\*kwargs):
\-\> 2785 return gca().plot(
2786 \*args, scalex=scalex, scaley=scaley,
2787 \*\*({"data": data} if data is not None else {}), \*\*kwargs)
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\axes_axes.py:1690, in Axes.plot(self, scalex, scaley, data, \*args, \*\*kwargs)
1688 lines = \[\*self.\_get_lines(\*args, data=data, \*\*kwargs)\]
1689 for line in lines:
\-\> 1690 self.add_line(line)
1691 if scalex:
1692 self.\_request_autoscale_view("x")
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\axes_base.py:2304, in \_AxesBase.add_line(self, line)
2301 if line.get_clip_path() is None:
2302 line.set_clip_path(self.patch)
\-\> 2304 self.\_update_line_limits(line)
2305 if not line.get_label():
2306 line.set_label(f'\_child{len(self.\_children)}')
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\axes_base.py:2327, in \_AxesBase.\_update_line_limits(self, line)
2323 def \_update_line_limits(self, line):
2324 """
2325 Figures out the data limit of the given line, updating self.dataLim.
2326 """
\-\> 2327 path = line.get_path()
2328 if path.vertices.size == 0:
2329 return
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\lines.py:1029, in Line2D.get_path(self)
1027 """Return the `~matplotlib.path.Path` associated with this line."""
1028 if self.\_invalidy or self.\_invalidx:
\-\> 1029 self.recache()
1030 return self.\_path
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\matplotlib\\lines.py:681, in Line2D.recache(self, always)
679 self.\_x_filled = self.\_x.copy()
680 indices = np.arange(len(x))
\--\> 681 self.\_x_filled\[nanmask\] = np.interp(
682 indices\[nanmask\], indices\[\~nanmask\], self.\_x\[\~nanmask\])
683 else:
684 self.\_x_filled = self.\_x
File \<__array_function__ internals\>:200, in interp(\*args, \*\*kwargs)
File \~.conda\\envs\\fondamenti-di-automatica\\lib\\site-packages\\numpy\\lib\\function_base.py:1595, in interp(x, xp, fp, left, right, period)
1592 xp = np.concatenate((xp\[-1:\]-period, xp, xp\[0:1\]+period))
1593 fp = np.concatenate((fp\[-1:\], fp, fp\[0:1\]))
\-\> 1595 return interp_func(x, xp, fp, left, right)
ValueError: array of sample points is empty
I discovered the problem is a bug in the version 3.7.0 of matplotlib. I installed the version 3.5.3 and now it works well. To install this version for your jupyter notebook open your anaconda terminal and type:
conda install matplotlib=3.5.3