I have been trying use the NyquistPlot function to generate a NyquistPlot for the following transfer function:
gLT = (3.55310^-15 s^4 - 0.1642s^3 - 0.1243 s^2 - 0.00161s + 10^-17) / (s^4 + 2.941 s^3 + 0.03508s^2 + 0.01522 s - 1.245*10^-15)
(the Pitch Dynamics for an F16 fighter)
However, when I execute a Nyquist Plot of this in Mathematica, it does not produce the correct result (Matlab and Scilab do produce correct plots).
The Scilab program appears below:
// This file is a test of the Nyquist function in Scilab. It is for an F16 pitch
// dynamics.
s = poly(0, "s")
gstf = syslin("c", (3.553e-15 * s^4 - 0.1642 * s^3 - 0.1243 * s^2 -0.00161 * s + 9.121e-17) ...
/ (s^5 + 1.825 * s^4 + 2.941 * s^3 + 0.03508 * s^2 + 0.01522 * s - 1.245e-15))
nyquist(gstf)
and the plot produced is:
A Mathematica Notebook with the issues is below
One can see that the Mathematica Nyquist Plot is completely wrong.
Does anyone know what is going on here?
Thanks in advance for any assistance.
Regards,
Yes ,probably is a bug in NyquistPlot .
I tried your example in Matlab and give the same plot what you wrote earlier.
You may write to WRI and you will find out what they will say.
Regards M.I.
maherkm
June 10, 2024, 12:54pm
3
Hello, use Chop[] so that you get a similar plot
NyquistPlot[Chop[gLTTf], PlotRange -> {{-6, 1}, {-3, 3}},
AspectRatio -> Full, Exclusions -> None]
Why is dosen’t work with my code ? See below:
maherkm
June 10, 2024, 1:26pm
5
When using Rationalize you have set the tolerance to 0.
gLT = Rationalize[ (
3.553*10^-15*s^4 - 0.1642*s^3 - 0.1243*s^2 - 0.00161*s +
9.121*10^-17)/(
s^5 + 1.825*s^4 + 2.941*s^3 + 0.03508*s^2 + 0.01522*s -
1.245*10^-15), 10^-14];
subat
June 10, 2024, 4:14pm
6
There’s a bug in computing the default frequency range. This is a workaround.
NyquistPlot[gLT, {-3, 3}, PlotPoints -> 200, MaxRecursion -> 10]
Suba,
Thanks for the help. I was surprised that there is still such a bug in NyquistPlot. This function has been in Mathematica forever.
Anyway, thanks again for clearing up the issue. Much appreciated.
Regards,
Robert Betz
