function of roots

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)?

[Jan]

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]

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.

Answer 1

[Walter Roberson]

roots() is to find the roots of a polynomial that has the given coefficients. The opposite of it is poly.

This is described right in the documentation, http://www.mathworks.com/help/techdoc/ref/poly.html