# Expressing polynomial including a indefinite parameter

5 views (last 30 days)
Cagas Akalin on 21 Oct 2021
Edited: Matt J on 21 Oct 2021
Hi All,
I know that the expression p=[1 -4 2] corresponds to p(x) = x^2 - 4x + 2.
I want to express p(x) = a*x^2 - 4x + 2-a
I would appreciate it if you told me how to do that.
Bests,
Cagdas

Matt J on 21 Oct 2021
Edited: Matt J on 21 Oct 2021
One way.
p = @(x,a) polyval([a,-4,2-a],x);
Usage:
x=1; a=2;
p(x,a)
ans = -2
Cagas Akalin on 21 Oct 2021
Thank you Matt,
It works.
Bests,
Cagdas

Matt J on 21 Oct 2021
Edited: Matt J on 21 Oct 2021
Possibly you mean that you want a coefficient vector as the output, rather than a polynomial in functional form.
syms a x
P = 2*a*x^2 - 4*x + 2-a
P = p=subs(P,x,1)
p = coefficients = sym2poly(p)
coefficients = 1×2
1 -2
Matt J on 21 Oct 2021
Yes, what I was trying to implement was exactly that you guessed.
Since my question covers an different topic in the bigger picture I will pose it in an another question page.
Yes, by all means.