# Symbolic seems to have an error

2 views (last 30 days)
Stephen Wilkerson on 11 Sep 2020
Edited: Paul on 12 Sep 2020
Two typos in my original post corrected

John D'Errico on 11 Sep 2020
Then why did you feel the need to post it again? Just edit your original post. Anyway, it seems like everytime you don't understand a piece of code, you declare it to be a bug.
Stephen Wilkerson on 11 Sep 2020
We'll do you have an answer?

Stephen Wilkerson on 11 Sep 2020
Yes that's what I ended up doing.

Stephen Wilkerson on 11 Sep 2020
Now I'm unsure how to delete the second post?

Paul on 11 Sep 2020
Edited: Paul on 12 Sep 2020
The RHS of your differential equation should be 3*u.
In the frequency domain, Y(s) = H(s)*U(s). It looks like you're trying to get the step repsonse of your second order system, so U(s) = 1/s. You forgot to multiply by U(s) in your symbolic approach.
num = 3;
den = [1 2 5];
syms s
nums = poly2sym(num,s);
dens = poly2sym(conv(den,[1 0]),s); % here!
ilaplace(nums/dens)
ans =
3/5 - (3*exp(-t)*(cos(2*t) + sin(2*t)/2))/5

#### 1 Comment

Stephen Wilkerson on 11 Sep 2020
Thank you

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