Increase amount of data extracted from Nyquist plot

Hi,

I already have extracted data from my nyquist plot with the following code:

linearSystemAnalyzer('nyquist',(zp+zt)); %zp+zt is my transfer function

[re,im] = nyquist(zp+zt);
Re = squeeze(re);
Im = squeeze(im);

This code extracted 437 values for each Re and Im. The Real part values were in an interval of [-7; 800]

Now I need to have more detailed data. So I want to have more values extracted from the nyquist plot. I already tried out the following code:

linearSystemAnalyzer('nyquist',(zp+zt)); %zp+zt is my transfer function

increase_number_of_values = [0 : 1 : 1000]; 

[re,im] = nyquist((zp+zt), increase_number_of_values);
Re = squeeze(re);
Im = squeeze(im);

This did get me more values. But for example the values of the Real part were in an interval of [-7;10] so the distance between each value simply got very very small and I got 1001 values in this interval.

However I want more values spread over the entire interval Re = [-7;800] and not just in Re = [-7;10].

The same applies to the values of the Imaginary part.

Has anybody an idea how to figure this out?

Thanks very much for your help!

Answer 1

[Mrunmayee Gaikwad]

Hi,

The nyquist function when used as nyquist(sys,w), w is specified as the frequency interval for your particular system. So, using 0 : 1 : 1000 in the function, you are defining the frequency interval as {0,1000} and that could be the reason for not getting the desired result.

You can define w = linspace(w1,w2,1000), where {w1,w2} is the frequency interval and 1000 is the number of points between this interval.

Refer to this example for more information: Create Nyquist Plot of Identified Model With Response Uncertainty