dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

kent-and@xxxxxxxxx wrote:
> > kent-and@xxxxxxxxx wrote:
> > > > Anders Logg wrote:
> > > > > On Wed, Aug 20, 2008 at 04:17:11PM +0200, kent-and@xxxxxxxxx wrote:
> > > > > > > kent-and@xxxxxxxxx wrote:
> > > > > > > > > Can Assembler::assemble_system be easily generalised to an Array
> > > > > > > > > of
> > > > > > > > > DirichletBC,
> > > > > > > > >
> > > > > > > > >    Array<DirichletBC*> bcs
> > > > > > > > >
> > > > > > > > > so that vector equations can be handled?
> > > > > > > > >
> > > > > > > > > Garth
> > > > > > > > Good point, I'll have a look.
> > > > > > > OK, I'm taking a look at the moment with a view to generalising
> > > > > > > Assembler::assemble_system for nonlinear problems (Newton solve).
> > > > > > >
> > > > > > > Garth
> > > > > > OK, in the present implementation, the matrix does not have 1 on the
> > > > > > diagonal
> > > > > > associated with bcs. It will be 1 times the number of elements (or
> > > > > > faces)
> > > > > > associated
> > > > > > with it.
> > > > > >
> > > > > > This weighting can be stored but it is not presently done.
> > > > > >
> > > > > > Kent
> > > > > I amazed you even managed to implement that code. It's huge. We should
> > > > > try to break it up so we can reuse as much as possible between that
> > > > > and the standard assemble() function.
> > > > I was impressed :).
> > > >
> > > > Now that what's needed is clear, it can be broken up. It looks to me
> > > > like a number of the existing functions can be extended slightly and
> > > > then re-used. The actual code for applying the bcs is not very long.
> > > >
> > > > Garth
> > > It is a mess,  way to large and should be broken up.
> > > It is also a bit "difficult" to break up. For instance, the
> > > coefficents may or may not need to be computed depending
> > > on whether it has been computed earlier ie. after computing coefficients
> > > for a macro element it should not be needed when computing the cell
> > > integral.
> > > The same applies to dof_maps.
> > Is there so much overhead involved in this? We're probably recomputing
> > these things in the other assembly functions. Perhaps there is
> > noticeable overhead, and that's why assemble_system is faster?
>
> The other functions recompute. And there are some recomputations
> in assemble_systems also. I guess avoiding these recomputations
> and fewer matrix insertions is the reason for speed up. I don' know
> which matter most.

Let's keep the mega-function and add a broken up version along side so 
that we can compare performance before removing it.

> > Hence it is hard to group everything associated
> > > with eg a cell integral together in a function. Or maybe it can be done
> > > with a set
> > > of bools that contains the state of the various structures.
> > I'm testing now whether an Array of boundary condition can be applied as
> > simply as I think. If that works, assemble_system should be fully
> > functional and we can try breaking it up.
>
> Great!

Seems like Arrays of bcs was really easy. I've pushed the changes.

Garth


> Kent