Extracting the coefficient of a polynomials matrix

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Qian Feng
Qian Feng on 30 Oct 2016
Edited: Qian Feng on 28 Mar 2017
I want to extract the coefficients of a polynomial matrix P(x) with sym x, which can be decomposed into P0 + P1x + P2x^2 ....
A example can be sym x
P = [1 + x x^2; x^3 x^4];
I understand that one might apply the function coeffi to each entry of P(x) to handle this problem. However, I wonder if there are more efficient ways to achieve this task.

Accepted Answer

Kwin on 30 Oct 2016
You could differentiate and evaluate P at x=0, so
P0 = subs(P, x, 0);
P1 = subs(diff(P), x, 0);
P2 = subs(diff(P,2)/2, x, 0);
P3 = subs(diff(P,3)/factorial(3), x, 0);
P4 = subs(diff(P,4)/factorial(4), x, 0);
would give you your matrices.
In general the nth polynomial matrix of P can be found with,
Pn = subs(diff(P,n)/factorial(n), x, 0);

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