4th degree equations

3 次查看（过去 30 天）

Asatur Khurshudyan 2011-11-18

Hi, can anyone help me with this problem? We need the smallest positive real root of this equation

a*x^4+b*x^3+c*x^2+d*x+e=0,

where a>0, b<0, c>0, d<0 and e>0. As Descartes said, in that case this equation has at least 2 positive real roots.

Thank you for your attention.

Walter Roberson 2011-11-18

r = roots([a,b,c,d,e]);
r(imag(r)~=0) = [];  %remove complex
r(r <= 0) = [];  %remove non-positive
min(r)  %now it is the smallest positive real root

Walter Roberson 2011-11-19

I think I do not know enough polynomial theory to come up with a useful answer on this, sorry.

No, I mean with Matlab. If there exist exact method, than it must be done by mathlab, I suppose. All right, as you wish.

在 Help Center 和 File Exchange 中查找有关 Linear Algebra 的更多信息

Find the treasures in MATLAB Central and discover how the community can help you!

Translated by