Python控件包-提高Nyquist绘图的分辨率

Question

我使用Python控制模块来绘制传递函数的Bode和Nyquist图。代码非常简单，如下：

# Simple Nyquist plotting

import control
import matplotlib.pyplot as plt

num = 5
den = [1,6,11,6]

#Creating a transfer function G = num/den
G = control.tf(num,den) 

control.nyquist(G)
plt.grid(True)
plt.title('Nyquist Diagram of G(s) = 5/(s+1)(s+2)(s+3)')
plt.xlabel('Re(s)')
plt.ylabel('Im(s)')
plt.show()

绘制了Nyquist图：

​

我想知道是否有可能增加点数的图表，提高它的分辨率。

Answer 1

python-control库遵循类似matlab的语法，所以最好先检查是否可以像matlab那样进行检查。这一次确实是。实际上，您可以查看函数签名以获得提示。

例如，在IPython终端中，如果我们键入

cnt.nyquist? 

我们会得到

Signature: cnt.nyquist(syslist, omega=None, Plot=True, color='b', labelFreq=0, *args, **kwargs)
Docstring:
Nyquist plot for a system

Plots a Nyquist plot for the system over a (optional) frequency range.

Parameters
----------
syslist : list of Lti
    List of linear input/output systems (single system is OK)
omega : freq_range
    Range of frequencies (list or bounds) in rad/sec
Plot : boolean
    If True, plot magnitude
labelFreq : int
    Label every nth frequency on the plot
*args, **kwargs:
    Additional options to matplotlib (color, linestyle, etc)

Returns
-------
real : array
    real part of the frequency response array
imag : array
    imaginary part of the frequency response array
freq : array
    frequencies

Examples
--------
>>> sys = ss("1. -2; 3. -4", "5.; 7", "6. 8", "9.")
>>> real, imag, freq = nyquist_plot(sys)
File:      c:\python34\lib\site-packages\control\freqplot.py
Type:      function

因此，对于您的情况，修复起来很简单。

num = 5
den = [1,6,11,6]

#Creating a transfer function G = num/den
G = control.tf(num,den) 
w = numpy.logspace(-3,3,5000)
control.nyquist(G,w);

Answer 2

请注意，在图中，所有数据点都存在。你只要把窗户放大，你就会看到所有的点。

您可以手动完成此操作(只需扩大绘图窗口)，也可以在显示结果之前进行set the plot window in Matplotlib：

If you've already got the figure created you can quickly do this:

fig = matplotlib.pyplot.gcf()
fig.set_size_inches(18.5, 10.5)
fig.savefig('test2png.png', dpi=100)

若要将大小更改传播到现有gui窗口，请添加forward=True

fig.set_size_inches(18.5, 10.5, forward=True)