[R] solving cubic/quartic equations non-iteratively

[Peter Dalgaard]

Mads Jeppe Tarp-Johansen 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?

As far as I know, we don't even have the quadratic...

They can't be hard to implement, though. However, you may need to take
care that non-iterative solutions are not necessarily more precise or
even faster than iterative ones. There may be cancellation issues and
the closed-form expressions can be complicated and involve slow function
calls.


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