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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [math] ODE step size
Date Thu, 02 Jul 2009 19:19:22 GMT
Angelo Port a écrit :
> Hello,
> 
> Is it possible to change the step size parameters on an ODE integrator prior
> to calling/running the integrator? For example, I would like to control the
> step size according to the size of the integration time. I am using the
> DormandPrince54Integrator.

The Dormand-Prince 5(4) integrator is an adaptive stepsize integrator.
This means it handles the step size by itself automatically, changing it
as needed during integration according to error control parameters. The
min and max value of the step size as well as the error control tuning
parameters are set at construction time. They cannot be changed
afterwards (and the step size will change within these prescribed limits).

What you can change however is an output step size (for example to print
the current state at regular intervals). This has nothing to do with the
internal varying integration step size. Changing the output step size is
done by registering a StepNormalizer which itself would wrap your own
fixed step handler. The normalizer will take care to convert the varying
internal step size to your desired fixed step size. Is it this kind of
feature you need ? We can explain in more details how to use it if you want.

There are also fixed step size integrators but their step size is also
fixed at build time and cannot be changed afterwards.

Luc

> 
> Angelo


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