dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Mon, Jul 04, 2011 at 11:46:00PM +0100, Garth N. Wells wrote:
>
>
> On 04/07/11 23:37, Anders Logg wrote:
> > On Mon, Jul 04, 2011 at 11:28:56PM +0100, Garth N. Wells wrote:
> >>
> >>
> >> On 04/07/11 17:22, Anders Logg wrote:
> >>> On Mon, Jul 04, 2011 at 04:47:46PM +0100, Garth N. Wells wrote:
> >>>>
> >>>>
> >>>> On 04/07/11 16:44, Anders Logg wrote:
> >>>>> On Mon, Jul 04, 2011 at 04:39:04PM +0100, Garth N. Wells wrote:
> >>>>>> I'm not sold on the NonlinearVariationalProblem interface. I would
> >>>>>> prefer a constructor takes the Jacobian as an argument. It's much
> >>>>>> cleaner to do things at construction and removes the need to later
> >>>>>> attach the Jacobian.
> >>>>>
> >>>>> The point is that one should be able to define a nonlinear problem
> >>>>> with or without a Jacobian. Not all nonlinear solvers need a Jacobian.
> >>>>>
> >>>>
> >>>> That's why I wrote 'a' constructor. We can have two versions.
> >>>
> >>> Yes, that's an option. The drawback with that is that it would double
> >>> the number of constructors (from 6 to 12) but it's a small thing to
> >>> fix. I wouldn't mind moving it to the constructor.
> >>>
> >>
> >> I think that we can rationalise the number of constructors in
> >> FooVariationalProblem. For the shared pointer versions, it would be
> >> enough to have just
> >>
> >>     LinearVariationalProblem(boost::shared_ptr<const Form> a,
> >>          boost::shared_ptr<const Form> L,
> >>          boost::shared_ptr<Function> u,
> >>          std::vector<boost::shared_ptr<const BoundaryCondition> > bcs);
> >>
> >> and
> >>
> >>     NonlinearVariationalProblem(boost::shared_ptr<const Form> F,
> >>          boost::shared_ptr<const Form> J,
> >>          boost::shared_ptr<Function> u,
> >>          std::vector<boost::shared_ptr<const BoundaryCondition> > bcs);
> >
> > I think it's important that we keep the same argument order as for the
> > reference versions, and that the Jacobian comes last to emphasize
> > that it is an optional/auxiliary argument. It also removes some of the
> > confusion we had be for with (a, L) vs (F, J). How about this:
> >
> >   LinearVariationalProblem(boost::shared_ptr<const Form> a,
> >                            boost::shared_ptr<const Form> L,
> >                            boost::shared_ptr<Function> u,
> >                            std::vector<boost::shared_ptr<const
> >                            BoundaryCondition> > bcs);
> >
> >   NonlinearVariationalProblem(boost::shared_ptr<const Form> F,
> >                               int rhs,
> >                               boost::shared_ptr<Function> u,
> >                               std::vector<boost::shared_ptr<const
> >                               BoundaryCondition> > bcs,
> >                               boost::shared_ptr<const Form> J);
> >
> > Same as your suggestion (just one shared ptr constructor in each
> > class) but placing the Jacobian last and keeping the right-hand side
> > in there.
> >
>
> I'm don't mind the order being the same (I didn't pay any attention to
> it). My main point is that the shared_ptr interface is lower level so we
> don't need to provide multiple convenience versions.

Agree.

> > Keeping the right-hand side is important since it makes it possible to
> > check for errors (like a nonzero right-hand side) in one single
> > place (inside NonlinearVariationaProblem.cpp). We would otherwise need
> > to check it inside Equation.cpp and possibly in the Python layer.
> >
>
> I don't like it. It makes the nonlinear interface clumsy. Reading
> the signature it's not clear to me what it's for or what I should
> pass in.

The point is that it makes the interface for all variational problems
(linear or nonlinear) the same:

  lhs, rhs, solution, [bcs], [jacobian]

I think this is helpful to minimize errors.

The docstrings in the FooVariationalProblem classes can be expanded to
explain the arguments in more detail.

--
Anders