Nyquist plot with logarithmic amplitudes

This is a port of Trond Andresen's MATLAB version for GNU Octave. To use it the control package needs to be installed.

Nyquist plot with logarithmic amplitudes

Quick start

Place the file nyqlog.m in Octave's path (see Manipulating the Load Path). Then load the control package and define a transfer function. Finally call the nyqlog function passing as argument the transfer function.

octave:1> pkg load control
octave:2> sys = zpk([-1/3 -1/2], [0 -0.02 -0.1 -2 -10], 48)

Transfer function 'sys' from input 'u1' to output ...

                     48 s^2 + 40 s + 8
 y1:  ------------------------------------------------
      s^5 + 12.12 s^4 + 21.44 s^3 + 2.424 s^2 + 0.04 s

Continuous-time model.
octave:3> nyqlog(sys)

Bonus: dark theme

This ported version of the function takes the colors from the variables defined and used by Octave to render the figures: defaultFigureColor and defaultAxesXColor. If you have customized these variables in Octave's configuration file, the function will automatically use those colors as well.

Nyquist plot with logarithmic amplitudes. Custom figure colors.