dolfin team mailing list archive

[Johan Hake <johan.hake@xxxxxxxxx>]

On Tuesday April 26 2011 13:44:22 Anders Logg wrote:
> On Tue, Apr 26, 2011 at 01:35:54PM -0700, Johan Hake wrote:
> > On Tuesday April 26 2011 13:27:10 Anders Logg wrote:
> > > On Tue, Apr 26, 2011 at 01:16:34PM -0700, Johan Hake wrote:
> > > > On Tuesday April 26 2011 10:41:50 Anders Logg wrote:
> > > > > On Tue, Apr 26, 2011 at 10:23:35AM -0700, Johan Hake wrote:
> > > > > > Hello!
> > > > > > 
> > > > > > (Sorry for the spamming, the previous email was prematurely
> > > > > > sent...)
> > > > > > 
> > > > > > I am about to use DOLFIN to solve a set of distrinct ODEs. The
> > > > > > ODEs are a result of an operator splitting of a PDE, avoiding an
> > > > > > expensive reassemble each newton itteration.
> > > > > > 
> > > > > > Each ODE is potentially small but it needs to be solved for each
> > > > > > node on a mesh. Each one of the ODEs are decoupled from
> > > > > > eachother.
> > > > > > 
> > > > > > What do you think would be fastest:
> > > > > >   1) To solve each small ODE using a DenseMatrix and a direct
> > > > > >   solver 2) Put all the small dense matrices into a big sparse
> > > > > >   one and go for an
> > > > > >   
> > > > > >      iterative solver.
> > > > > > 
> > > > > > For the last one I need to construct my own assembler, iterating
> > > > > > over the degrees of freedom.
> > > > > 
> > > > > I think Option (1) since it can be easily and efficiently
> > > > > parallelized.
> > > > 
> > > > Ok.
> > > > 
> > > > > You could also consider checking out the ODECollection class.
> > > > 
> > > > Has this been tested, and are there any example of how to use the
> > > > ODECollection? What ODE solver is used to solve the ODE. I do not
> > > > need any multi adaptive ODE solver ;), just an implicit fast and
> > > > rock stable one.
> > > 
> > > You can choose between cG(q) and dG(q) for any q, and it can be either
> > > mono- or multi-adaptive, or not adaptive at all.
> > 
> > Ok
> > 
> > > The ODECollection class is untested and probably doesn't work so it
> > > might need some love.
> > 
> > Well, I need some love right now, so I will probably not spend time
> > pouring love over something that will be changed... I also see that the
> > TimeStepper still holds the solution vector, and for a big ODECollection
> > that would mean a lot of copying. Not sure this would be the biggest hog
> > though?
> 
> The idea is to have one big solution vector but work through offsets
> in the ODECollection class. Anyway, it's probably good to stay away
> from it since it might change rapidly or be removed.

Ok. I'll stay out of it...

> > > Anyway, the plan is to move much of the functionality for solving ODEs
> > > into FFC and generate code for in the same way as we do for assembling
> > > PDE systems so much of the ODE code might be removed or rewritten in
> > > the near future.
> > 
> > Sounds very cool! Do you have any person to do the job? I am not offering
> > myself ;) Are the potential heart (bi/mono-domain) solver included in the
> > greated scheme here?
> 
> Yes, Benjamin, Marie and myself (post 1.0 and book).

Nice!

Johan

> --
> Anders
> 
> _______________________________________________
> Mailing list: https://launchpad.net/~dolfin
> Post to     : dolfin@xxxxxxxxxxxxxxxxxxx
> Unsubscribe : https://launchpad.net/~dolfin
> More help   : https://help.launchpad.net/ListHelp