On Sat, Nov 28, 2009 at 12:47:40AM -0800, Johan Hake wrote: > On Friday 27 November 2009 23:59:52 Johan Hake wrote: > > Hello! > > > > I have not pushed anything, but Expressions should be up to shape now, and > > I am working on simplifying the logic in other places of expression.py > > > > I do not like the implementation of the dim method. It is used to read a > > user defined value dimension and then discarded. I suggest that we add a > > value_shape attribute to the dolfin.Expression class. If not set by the > > user it is by default (), i.e., a scalar Expression. > > > > class MyExpression(Expression): > > value_shape = (2,) > > def eval(self, values, x): > > values[0] = 1 > > values[1] = 1 > > > > The dim name is also only making sense for Vector Expressions, where I > > think a value_shape attribute makes sense for all occasions. A value_shape > > for scalar Expression will still be the default. > > > > After creation and instantiation we then have an object that have both a > > shape method (from ufl.Function) and a value_shape attribute from the > > subclassing definition. > > > > What you think. > > Hmm, more trouble I think. How should we be able to specify the degree, and or > element when we have derived python Expression? Should we add more > attributes?
I think it works to do
f = MyExpression(element=FiniteElement("Lagrange", triangle, 3))
Or is that broken?
--
Anders
> One way is to adapt the CompiledExpression solution, and to make
> dolfin.Expression a pure and nice subclass of ufl.Function and cpp.Expression.
> a user defined python Expression would then look like:
>
> class MyExpression(Expression):
> def __init__(self):
> Expression.__init__(self, element, degree, value_shape)
> def eval(self, values, x):
> values[0] = 1
> values[1] = 1
>
> Where element, degree, and value_shapes are all optional. All the logic of
> what element, should be used is concealed in dolfin.Expression.__init__
>
> With this solution we split all the logic that goes into a compiled Expression
> from what goes into a user defined Python Expression. One of the main problems
> with the present design is that they are too intermingled.
>
> Johan
>
> > Johan
> >
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