dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

On Sun, Sep 05, 2010 at 03:48:10PM +0100, Garth N. Wells wrote:
>
>
> On 05/09/10 15:22, Anders Logg wrote:
> >On Fri, Sep 03, 2010 at 04:36:40PM -0700, Johan Hake wrote:
> >>Hello!
> >>
> >>Garth found an ambiguity in the Expression doc string regarding how a user
> >>should initiate a user defined Expression (not a compiled one) in Python. If
> >>the Expression is vector or tensor valued the user need to provide information
> >>about this.
> >>
> >>This can be done in two ways. Either overload the dim method or provide a ufl
> >>FiniteElement while instantiating the Expression. Neither of these methods are
> >>documented in the docstring.
> >>
> >>In the mixed poisson demo both dim and rank are overloaded. I think rank is
> >>not needed (works fine without). However dim is just a method introduced to be
> >>able to automatically select a FiniteElement.
> >>
> >>First I am not sure dim is the correct name. We could use value_size as this
> >>is present in the GenericFunction interface for just this purpose. Second I am
> >>not sure overloading a method is the best and most clear way to provide this
> >>information. Maybee he could do it while instantiating the Expression instead?
> >>
> >>   class BoundarySource(Expression):
> >>       def eval_data(self, values, data):
> >>           g = sin(5*data.x()[0])
> >>           values[0] = g*data.normal()[0]
> >>           values[1] = g*data.normal()[1]
> >>
> >>   s = BoundarySource(value_size=2)
> >>
> >>Or just use the FiniteElement which is a litle bit over kill but already
> >>possible as it is.
> >>
> >>   s = BoundarySource(element=BDM.ufl_element())
> >>
> >>What you say?
> >
> >I'm not sure what the names should be, other than that it would be
> >good to change as little as possible since we are getting closer to
> >1.0 and there have been numerous iterations back and forth on the
> >expression/function interface.
> >
> >Either way, it shouldn't be an argument to the constructor (from the
> >user side). It should be part of the class. Otherwise, it looks like
> >one can instantiate a BoundarySource thing for other value sizes when
> >the value size is fixed.
> >
>
> It's useful to set the element in the constructor. I use it to
> create interpolations of different degrees.
>
> Garth

Isn't it better then to do

  f  = MyExpression()
  f1 = interpolate(f, V1)
  f2 = interpolate(f, V2)

?

--
Anders