solving a cubic equation
342 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
vaggelis vaggelakis
le 20 Août 2014
Commenté : Christopher Creutzig
le 29 Août 2014
I am using the command
x = solve('a*x^3 + b*x^2 + c*x + d')
to get the polynomial's roots. It returns a symbolic answer. Then i evaluate the a,b,c,d and i do copy-paste the first symbolic answer and then "enter" to get a numerical answer.
The numbers i get (1 almost real and 2 complex, as it is expected) are not roots of the equation!
I am looking for the poles of a mechanical system, so the roots must exist... What am i doing wrong?
1 commentaire
Christopher Creutzig
le 29 Août 2014
Please provide the values for a, b, c, d with which you run into that problem.
Note that these solution formulas are well known to be numerically unstable. That may be the root of your problem. (No pun intended.)
Réponse acceptée
Star Strider
le 20 Août 2014
Maybe I’m missing something, but why use the Symbolic Math Toolbox at all for this?
x = roots([a b c d])
0 commentaires
Plus de réponses (0)
Voir également
Catégories
En savoir plus sur Assumptions dans Help Center et File Exchange
Produits
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!