| Thread Previous • Date Previous • Date Next • Thread Next |
On 05/09/10 17:22, Johan Hake wrote:
On Sep 5, 2010, at 8:47, Marie Rognes<meg@xxxxxxxxx> wrote:On 05. sep. 2010 17:36, Johan Hake wrote:On Sunday September 5 2010 07:26:19 Anders Logg wrote:On Sat, Sep 04, 2010 at 08:16:43PM +0200, Marie Rognes wrote:On 04. sep. 2010 18:26, Johan Hake wrote:On Saturday September 4 2010 03:54:35 Marie Rognes wrote:On 04. sep. 2010 01:36, 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.Thanks for bringing this up -- evidently I'm confused.Well, me too. Ever since Anders introduced the automatic selection of elements for the Expressions, I have been some what confused.Well, that part made perfect sense to me --- I think ;)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)I don't really like the name value_size, but this looks natural to me. What would it be for matrix-valued functions?As I have understand it, value_size is the size of the values array passed to the Expression. So that would then be: value_size = m x n I am not totally happy with the above code as the class should contain everything it needs to be instantiated correctly. Would it make more sense to change the name of dim to value_size?Exactly what do you mean here? Keep needing to supply a method "dim", but renaming it to "value_size" ? (I still don't find the name value_size very intuitive.)We have value_rank and value_dimension in the UFC interface. Those are well defined and well documented. value_size is not something the user should be worried about, but it is something that comes up in the code again and again when allocating arrays: int value_size = 1; for (int i = 0; i< value_rank; i++) value_size *= value_dimension(i) Another option would be to set value_shape which is int value_shape[value_rank]; for (int i = 0; i< value_rank; i++) value_shape[i] = value_dimension(i)What with: class MyExpression(Expression): def eval(value, x): some_tensor_expression def value_shape(self): return (2,2) If not given we assume, as today, that the value shape is (). One should be able to instantiate it using a not automatically chosen FiniteElement. We add check so the value shape agree with the passed Element.Side note: At the moment, we allow both specifying a finite element and/or a element function space. Should we really allow specifying element? Using element (instead of function space) from dolfin seems a bit odd to me.We do not accept a FunctionSpace today. We just silently take it and do nothing with it... Will fix. I think we landed on just the element as an Expression should not be tied to a mesh.
That's right - an expression can be evaluated for any x, which is why we use an element (if we use a function space, it's just a lazy way of passing the element). The optional element in the constructor tells the form compiler how to deal with the Expression, rather than having the form compiler choose the element.
Garth
Johan-- Marie _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp_______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@xxxxxxxxxxxxxxxxxxx Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
| Thread Previous • Date Previous • Date Next • Thread Next |
