12 Problem A8.14 OGATA 4ed(Nyquist plot)

Laplace.T	Root-locus	Transient response	Frecuency response

12 Problem A8.14 OGATA 4ed(Nyquist plot)
Let's draw the polar plot of positive and negative feedback transfer functions by Scilab

$\begin{displaymath}G(s)=\frac{s^{2}+4\cdot s+6}{s^{2}+5\cdot s+4}\end{displaymath}$
Scilab program
clf;

s=%s/(%pi*2);

g=-(s^2+4*s+6)/(s^2+5*s+4);

gs=syslin('c',g);

nyquist(gs);

g2=(s^2+4*s+6)/(s^2+5*s+4);

gs2=syslin('c',g2);

nyquist(gs2);

xstring(0.57,0.1,'Negative feedback');

xstring(-1.7,0.45,'Positive feedback');

mtlb_axis([-2 2 -0.5 0.5]);