How can I simulate a LTI system with complex data?

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Americo Cunha
Americo Cunha on 9 Feb 2011
Answered: Rahim Gholami on 11 Dec 2018
Hello,
I wrote a simple code to to simulate a LTI system:
% -----------------------------------------------------------
N = 200; t0 = 0.0;
t1 = 50.0;
T = t1-t0;
dt = T/(Nsteps-1);
time = (t0:dt:t1)';
f = zeros(N,1);
m = 1;
c = 1;
K = 5;
H = tf(1,[-m i*c k]);
h = impulse(H,time);
x = conv(f,h);
% -----------------------------------------------------------
But using the code above I receive the following message:
Cannot simulate the time response of LTI models with complex data.
Is there any way to compute the unit impulse response for a transfer function with complex entries?
I also appreciate other suggestions to solve this problem.
Thanks in advance.
Americo

Answers (3)

Gurudatha Pai
Gurudatha Pai on 18 Jun 2011
It looks like impulse() function does not take continuous time systems with complex coefficients; However, if I were to just solve this problem, you system has a unstable complex pole pair and no zeros. It would be a matter of using exponential functions with of the roots of denominator polynomial. Does that makes sense?

Rajiv Singh
Rajiv Singh on 19 Jun 2011
Simulation (time domain response calculation) of complex LTIs is not supported. You can cast is into a real system (as Gurudatha suggests), or convert your system into a model type used by System Identification Toolbox: H2 = idss(H); h2 = impulse(H2,time);

Rahim Gholami
Rahim Gholami on 11 Dec 2018
Hi. I want to use rlocus for a complex dynamic system.
Y=tf([1,3,2],[1,-1-i,i]);
rlocus(Y);
But I got the same eror.
Is there any way so that I can fix it?

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