# How do I make a plot with all three states [x1 x2 x3]' in SImulink?

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DB on 26 Nov 2020
Commented: DB on 4 Dec 2020
I have made a model on people [x1 x2 x3]' influencing each other by influence matrix A.
How can I plot the changes in the states over k (discrete) and time (continuous)?
The initial value is x0 which has values for
x = [x1 x2 x3]'
with
x0 = [12 7.57 5]'
And matrix A is a 3x3 matrix with unstable eigenvalues.
My discrete model looks like this:
And my continuous model ike this:
Paul on 3 Dec 2020
I'm not sure how much more (if any) help I can offer. I'm used to doing the opposite, i.e., starting with a continuous time model (differential equation) and then coming up with a discrete time approximation (difference equation). You seem to want to go the other way. One could come up with a differential equation that is approximated by the difference equation, but the outputs of those equations in response to the initial condition will not look like the plots you've posted.
The plot you posted shows a group of three (?) red lines and two blue lines. As best I can understand based on the problem description, the blue lines cannot be initial condition responses from discrete and continuous models where one model is the approximation of the other. One can come up with a model with two outputs that have the same appearance as the blue curves, but I wouldn't call that model a discrete model with a continuous approximation.
Sorry I couldn't be of more help.
DB on 4 Dec 2020
@Paul Thank you very much for your help. I do acknowledge I have a vague problem and I'll work on it further. I think your help has made me understand it a whole lot better.

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