How to extract coefficient of a certain term in Matlab?

For example,

syms f1 f2 a
pexpansion = f1 - f2 - a*(f1 - f2) + f2/a + a^2*(f1 - f2) - a^3*(f1 - f2) + a^4*(f1 - f2)

I want to extract the coefficient of power 1 of a, which is (f1-f2). However, there is 1/a term in the expression which makes it not a polynomial. Does anyone know how to do this?

Answer 1

[Star Strider]

Try this:

syms f1 f2 a
pexpansion = f1 - f2 - a*(f1 - f2) + f2/a + a^2*(f1 - f2) - a^3*(f1 - f2) + a^4*(f1 - f2);
pexpansion = expand(a * pexpansion);                            % Eliminate ‘a’ In Denominator
[cfs,trms] = coeffs(pexpansion, a);                             % Coeffients & Terms
Result = cfs(trms == a)                                         % Coefficient Of ‘a’

Result =
f1 - f2

[DmArcher]

Thank you so much

[Star Strider]

As always, my pleasure.