jury test code for stability in digital controls

Question

sara 2014-4-3

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编辑： Polat Alemdar 2022-11-13

I've been asked for a program that performs the jury test,could u help me please since i have never used matlab.

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Answer 1

zaynab El Mawass 2019-2-27

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https://ww2.mathworks.cn/matlabcentral/answers/124410-jury-test-code-for-stability-in-digital-controls#answer_363028

在 MATLAB Online 中打开

function  stability  = Jury(coef)
stability=0;
n=size(coef,2);
  if(polyval(coef,1)<0)
    stability=1;
    return
  end
if(mod((n-1),2)==0)
  if(polyval(coef,-1)<0)
    stability=2;
      return
  end
else
    if(polyval(coef,-1)>0)
     stability=2;
     return
    end
    if(abs(coef(1)>abs(coef(n))))
       stability=3;
       return
    end
    
    matrice=zeros(n,2*n-3);
    for i=1:1:n
        matrice(1,i)=coef(i);
        matrice(2,i)=coef(n-i+1);
    end
    
    for i=3:2:2*n-3
        for j=1:1:n-i+2
            matrice(i,j)=matrice(i-2,1)*matrice(i-2,j)-matrice(i-1,1)*matrice(i-1,j);
            matrice(i,n-j+1)=matrice(i,j);
            for k=2:1:j
                if(abs(matrice(i,k))>abs(matrice(i,1)))
                    stability=4;
                    
                else
                    stability=0;
                end
            end
        end
    end
end

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Walter Roberson 2019-2-27

zaynab, I notice that you set stability to 0 or 4 inside the nested for loops, but you do not store the values and you do not return or break upon detecting a particular value. That would result in later iterations overwriting the stability variable. That does not sound appropriate.

Polat Alemdar 2022-11-13

编辑：Polat Alemdar 2022-11-13

This function accepts only numerical inputs. So coefficients of the denominator of TF are determined. In this case, Jury's stability test does not needed. One can find the poles check locations of the poles (inside or outside the unit circle). Jury's stability test is useful for undetermined denominator coefficients.

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Answer 2

zaynab El Mawass 2019-3-14

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Hello Walter,

I used the return expression because there is no need to go further in the test if one of the cases is broken. The system is considered directly instable.

As for the numbers, they tell which Jury test condition led to the instability. This a symbolic way.

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Walter Roberson 2019-3-15

You do not have a break or return in your for i loop, so your loops keep going after you find a case 4.

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Answer 3

Le Truc 2019-5-14

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Hello Zaynab. I am come from Viet Nam. I tried your source code, but there is an error with my matlab : "Not enough input arguments". Can you help me to fix?