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GNU Octave Manual Version 3
by John W. Eaton, David Bateman, Søren Hauberg
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26.6 Miscellaneous Functions

Function File: poly (a)
If a is a square N-by-N matrix, poly (a) is the row vector of the coefficients of det (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 of poly (a).
=> 1.00000 + 0.00000i
=> 1.00000 - 0.00000i
=> 1.00000 + 0.00000i

In real-life examples you should, however, use the eig function 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.

See also eig, roots

Function File: polyout (c, x)
Write formatted polynomial
c(x) = c(1) * x^n + ... + c(n) x + c(n+1)

and return it as a string or write it to the screen (if nargout is zero). x defaults to the string "s".

See also polyval, polyvalm, poly, roots, conv, deconv, residue, filter, polyderiv, and polyinteg

Function File: polyreduce (c)
Reduces a polynomial coefficient vector to a minimum number of terms by stripping off any leading zeros.

See also poly, roots, conv, deconv, residue, filter, polyval, polyvalm, polyderiv, polyinteg

ISBN 095461206XGNU Octave Manual Version 3See the print edition