Re: GSL ode-initval development

[Brian Gough <bjg at network-theory dot co dot uk>]

At Sun, 31 Aug 2008 10:25:26 +0300,
Tuomo Keskitalo wrote:
> I have been writing a non-linear equation solver based on a modified 
> Newton iteration method, and a question about failures has come up. What 
> value should the non-linear equation solver return to the stepper (and 
> from there to user) in the case that the method reaches a maximum number 
> of Newton iterations and therefore fails? GSL_CONTINUE or GSL_FAILURE or 
> something else?

I'd suggest GSL_FAILURE to start with. Hopefully the solver won't fail
that often.

> which values of variables y should a stepper which uses step doubling 
> for error estimation return: The values from the single step or the 
> values from two half steps? You would expect to get the values of single 
> step from "a stepper", but the values from two half steps should be more 
> accurate, and they are available.

The final value of y should come from the two half steps as they are
more accurate.  See rk4.c for an example and the error estimate.

-- 
Brian Gough