Re: Biquadratic equation

[Ben Abbott]

On Aug 2, 2009, at 4:33 AM, address@hidden wrote:

> Hi,
>
> I have a simple request: How to get a solving of biquadratic  
> equation like 16x^4-4x^2-2=0 in GNU Octave. I dont have enough  
> skills to do it myself.
>
> Thanks

Octave has a nice function for solving for the roots of polynomials.

        x1 = roots ([16, 0, -4, 0, -2]);

 avoid reduce numerical errors ...

        x2 = (sqrt(roots([16 -4, -2]))*[1 -1])(:)

sort(x1)-[-0.5i;0.5i;1/sqrt(2);-1/sqrt(2)]
ans =

   0.0000e+00
   0.0000e+00
   7.7716e-16
  -8.8818e-16

sort(x2)-[-0.5i;0.5i;1/sqrt(2);-1/sqrt(2)]
ans =

   0.0000e+00
   0.0000e+00
   1.1102e-16
  -1.1102e-16

Ben