There are certainly formulas for solving polynomials numerically up to 4th
degree non-iteratively, but you will almost certainly get better results
using iterative methods.

Even the much more trivial formula for the 2nd degree (quadratic) is tricky
to implement correctly and accurately, see:

* George Forsythe, How do you solve a quadratic equation?
* Yves Nievergelt, How (Not) to Solve Quadratic Equations

Hope this helps.

           -s

On Tue, Jan 5, 2010 at 10:11 AM, Mads Jeppe Tarp-Johansen <
s02mjtj@math.ku.dk> wrote:

> To R-helpers,
>
> R offers the polyroot function for solving mentioned equations iteratively.
>
> However, Dr Math and Mathworld (and other places) show in detail how to
> solve mentioned equations non-iteratively.
>
> Do implementations for R that are non-iterative and that solve mentioned
> equations exists?
>
> Regards, Mads Jeppe
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

	[[alternative HTML version deleted]]

