On Tuesday 29 September 2009 22:39:02 Anders Logg wrote:
On Tue, Sep 29, 2009 at 10:29:14PM +0200, Johan Hake wrote:
On Tuesday 29 September 2009 22:10:54 Anders Logg wrote:
On Tue, Sep 29, 2009 at 08:55:03PM +0100, Garth N. Wells wrote:
I'm looking forward to seeing the new code. Is all the old
functionality still in place?
Yes and no. Everything except the generated CoefficientSet stuff
should still work in the C++ interface, but the Python interface won't
work until the corresponding changes have been made on the Python side.
Here's some more information about the changes:
1. Subclassing Function and overloading eval() has been replaced by
the Expression subclass which works in the same way with eval().
2. All the old functionality/logic of the Function class is still in
place but it can now be cleaned up and simplified.
3. A Function will now *always* have a FunctionSpace and *always* have
a vector.
Good!
4. An Expression *never* has a FunctionSpace and *never* has a vector.
Also good! Should we consider (re-)adding a value_rank and dimension
method to the expression class?
Yes, perhaps. But it's very convenient not having to specify it. We
could make it optional.
Ok. No big dealt for me. In Python we can solve this for Expressions anyway.
Also what would the preferred solution be for a Python expression. It
should not have a FunctionSpace but we need a FunctionSpace to initialize
the ufl.Function. Or rather the ufl.FiniteElement that comes with the
FunctionSpace.
I see two alternatives:
1) Instantiate an Expression with a FunctionSpace, then let the
FunctionSpace reside in the Python layer. The ufl.FiniteElement is used
to instantiate the ufl.Function.
2) Instantiate an Expression with a ufl.FiniteElement. The problem with
this is that we have not exposed the ufl.FiniteElement in the PyDOLFIN
interface previously. But the confusion with an expression having a
FunctionSpace is partly avoided.
In both cases I could add checks for rank and dimensions in the Python
layer if we decides to not require it for the C++ interface.
I think we discussed the possibility of detecting the value dimension
from the expression
Yes, but a user can initialize an Expression with the wrong
FunctionSpace/FiniteElement compared to what the expression looks like.
and automatically using piecewise linears if not
otherwise specified.
The function space could be an optional argument:
f = Expression("sin(x[0])", V=V)
We cannot automatically figure out the topological dimension, can we?
