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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





cajael