How to extract coefficient of a certain term in Matlab?

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DmArcher 2017-4-28

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/337754-how-to-extract-coefficient-of-a-certain-term-in-matlab

评论： Star Strider 2017-4-28

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?

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Answer 1

Star Strider 2017-4-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/337754-how-to-extract-coefficient-of-a-certain-term-in-matlab#answer_264863

在 MATLAB Online 中打开

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