Operate coefficients in Symbolic expressions

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Ignacio Fidalgo
Ignacio Fidalgo 2020-5-18
评论： Walter Roberson 2020-5-18
Hi,
I would like to know how to operate the coefficients in a symbolic expression.
Thanks!
Example:
syms s k kc
G_s=k/(s^3+6*s^2+10*s);
D_s=kc*(s+2)/(s+9.067);
t_s=(G_s*D_s)/(1+G_s*D_s);
vpa(simplify(t_s),5)
Result:
Desired result:

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回答（1 个）

Ameer Hamza
Ameer Hamza 2020-5-18
Maybe there is an easy option, but something like this will work
syms s k kc
G_s=k/(s^3+6*s^2+10*s);
D_s=kc*(s+2)/(s+9.067);
t_s=(G_s*D_s)/(1+G_s*D_s);
[n,d] = numden(t_s);
a = gcd(coeffs(n));
vpa(simplify((n/a)/(d/a)))
  2 个评论
Ignacio Fidalgo
Ignacio Fidalgo 2020-5-18
Thank you very much for your answer, but as you've said, i'm looking for an easier option. Maybe one already implemented in matlab, since this is a very simple example but it can get harder.
Walter Roberson
Walter Roberson 2020-5-18
There is no method implemented in MATLAB for this purpose. You are fighting against the internal rules for representation of ratios.
You could probably replace the last line with
vpa(n/a)/vpa(d/a)

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