Re: ode-initval implicit solvers and development

[Tuomo Keskitalo <Tuomo.Keskitalo@iki.fi>]

Hello,

On 02/01/2009 05:42 PM, Brian Gough wrote:

> - Currently the control object is only used by the multistep adams
> stepper.  What other types of methods might need access to the error
> control?

All steppers that do some kind of iterative solution internally. For 
example the methods that use Newton iteration.

> - In modnewton1.c there is the comment
> 
>     /* Stopping tolerance for Newton iteration */
>     /* FIXME: tol should be user defined */
> 
> How would you handle the newton tolerance--do we need a way to pass
> that in as well?

Yes, I think that is needed. This would be done similarly to msadams, 
e.g. modnewton1 asks the tolerance via gsl_odeiv_control_errlev.

I plan to implement the Newton iteration for BDF methods first, and then 
modify modnewton1. I'd also like to implement the implicit 5th order 
Radau method, which also needs Newton iteration. This will take some 
time. It might be best to wait until then to see what other changes I'll 
have to make to the ode-initval interfaces. Hopefully none.

> Valgrind detects an uninitialised variable in msadams.c, which is
> flagged with -Wall as well.

I'll add initialization to those, to get rid of the warnings, in the 
next release. Thanks for your comments!

I'd appreciate if anyone has the chance to test and report how msadams 
compares to other steppers in practice and if there are any problems 
with it!

-- 
Tuomo.Keskitalo@iki.fi
http://iki.fi/tuomo.keskitalo