Previous: Polynomial Interpolation, Up: Polynomial Manipulations
If a is a square N-by-N matrix,
poly (a)is the row vector of the coefficients ofdet (z * eye (N) - a), the characteristic polynomial of a. As an example we can use this to find the eigenvalues of a as the roots ofpoly (a).roots(poly(eye(3))) 1.00000 + 0.00000i 1.00000 - 0.00000i 1.00000 + 0.00000iIn real-life examples you should, however, use the
eigfunction for computing eigenvalues.If x is a vector,
poly (x)is a vector of coefficients of the polynomial whose roots are the elements of x. That is, of c is a polynomial, then the elements of d= roots (poly (c))are contained in c. The vectors c and d are, however, not equal due to sorting and numerical errors.