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Next: 4 Example 8-11 OGATA Up: FrequencyResponse Previous: 2 Example 8-6 OGATA   Contents

 

3 Example 8-10 OGATA 4ed(Nyquist plot)



    Let's plot Nyquist plot by Scilab.

    \begin{displaymath}G(s)=\frac{1}{s^{2}+0.8\cdot s+1}\end{displaymath}

    Scilab program 
    clf;

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

g=1/(s^2+0.8*s+1);

gs=syslin('c',g);

nyquist(gs);

xgrid;

xtitle('Nyquist plot of 1/(s^2+0.8*s+1)')

     

    Image Ejemplo8-10Pag532
    As we see we only plot the part that goes $w=0$ to $w=\infty$.

    Let's do it from $w=-\infty$ to $w=\infty$

     

    Scilab program 
    clf;

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

s1=-s;

g=1/(s^2+0.8*s+1);

g1=1/(s1^2+0.8*s1+1);

gs=syslin('c',g);

gs1=syslin('c',g1);

nyquist(gs);

nyquist(gs1);

mtlb_axis([-2 2 -2 2])

xtitle('Nyquist plot of 1/(s^2+0.8*s+1)')

     

    Image Ejemplo8-10bPag533