Question
How can I fix this error? sys=tf([1 1 1 1],[1 1]); t=0:0.1:10; step(sys,t) ??? Error using ==> DynamicSystem.step at 84 Cannot simulate the time response of models with more zeros than poles. I know that my system is unstable but how can I receive an "unstable" graph for this system on my axes?
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Expert Answer
Kshitij Singh
PhD Expert
Answered Aug 21, 2026
Just FYI the following code won't provide the same graph has the step function, it just plots the function having s as the variable, the step fuction just works for proper systems (n poles >= n zeros).
"Impulse response":
syms s
TFC=evalc('tf([1 1 1 1],[1 1])');
[a b] = strread(TFC, '%s %s', 'delimiter',char(10));
num=sym(char(a(2)));
den=sym(char(a(3)));
ezplot(num/den,[0 100])
"Step response"
syms s
TFC=evalc('tf([1 1 1 1],[1 1 0])');
[a b] = strread(TFC, '%s %s', 'delimiter',char(10));
num=sym(char(a(2)));
den=sym(char(a(3)));
ezplot(num/den,[0 100])
The scales aren't the same like you get with the step function.
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