Alan Miller wrote:
> ----- Original Message -----
> From: "Aleksandar N. Donev" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, February 18, 2003 2:14 AM
> Subject: Quartic equations
>
>
>
>>Hello,
>>
>>Does someone have a routine for a quartic polynomial root solver? I need
>>to find the smalles real positive root of a quartic polynomial or know
>>that it does not exist. In cases when it does exist, it is likely that I
>>have a very good initial guess just by solving the corresponding quadratic
>>equation (ignoring two terms, since they are small!), but simply deciding
>>whether there is a positive real root seems hard (Sturm sequences?). The
>>code will be used in public-domain libraries.
>>
>>Any advice from the experiences appreciated.
>>Snowed-In Aleksandar
>
>
> You will find qtcrt.f90 at my web site, in the code from the NSWC library.
>
> Cheers
>
> Alan Miller
> http://users.bigpond.net.au/amiller
> Retired Statistician
A by the way. What application do you have for this, Aleksander? I use
a quartic in calculating certain initial conditions of induction motors.
Since I have only ever written code to resolve a cubic, I scrounged the
original (F77 -- even F66 -- style) NSWC code. What I have seen of
Alan's F90 re-written TOMS and NSWC and the statistical stuff, I would
suggest that you pick up his code.
Since the quartic is a closed formula, finding the results and checking
those should be much speedier than trying to do any other logical testing.
Unlike several commercial packages, e.g. NAG (no slight intended), I do
believe in using the closed formulae for cubic and quartic rather than
generalised root finders; both for speed and accuracy.
Regards, Paddy
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