Le vendredi 03 juillet 2009 à 10:00 -0600, Charles R Harris a écrit : > What do you mean by erratic? Are the computed roots different from > known roots? The connection between polynomial coefficients and > polynomial values becomes somewhat vague when the polynomial degree > becomes large, it is numerically ill conditioned.
For an illustration of what I mean by 'erratic', see http://fsilva.perso.ec-marseille.fr/visible/script_als_nbmodes.png or http://fsilva.perso.ec-marseille.fr/visible/script_als_nbmodes.pdf with the real part of the roots on the left, and the imaginary part of the right: - for low orders (<26), a pair of complex conjugate roots appears when the order of polynomial is increased (with a step equal to 2). As expected in my physical application, their real parts are negative. - for higher order (>=26), there is no more 'hermitian symmetry' (complex conjugate solutions), and real parts become positive... The computation of the coefficients of the polynomial is out of topic, I already checked it and there is no errors. -- Fabrice Silva Laboratory of Mechanics and Acoustics - CNRS 31 chemin Joseph Aiguier, 13402 Marseille, France. _______________________________________________ Numpy-discussion mailing list [email protected] http://mail.scipy.org/mailman/listinfo/numpy-discussion
