function of roots

Question

Dwyane Wade 2011-8-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/13767-function-of-roots

采纳的回答： Walter Roberson

I have another problem it says:

give the function whose roots are 4, -3, -2, 1/5 and 0.

should I use poly(x) or roots(x)?

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Jan 2011-8-15

Does this question concern MATLAB? As far as I can see the polynomial with the shown roots can be created manually in some seconds.

Walter Roberson 2011-8-15

According to the poly() documentation, it uses eigenvalues. It says,

It is possible to prove that poly(A) produces the coefficients in the characteristic polynomial of a matrix within roundoff error of A. This is true even if the eigenvalues of A are badly conditioned. The traditional algorithms for obtaining the characteristic polynomial, which do not use the eigenvalues, do not have such satisfactory numerical properties.

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