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.) >>> 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? >>> >> When prescribing an element (or a function space) to anything that >> resembles a function, I assume that the function (in this case, the >> Expression) is interpolated into the function space defined by that >> element. Is that correct? >> > Yes, that is correct. We need a FiniteElement to be able to initiate the > ufl.Coefficient. If not provided we automatically choose one based on (for > now > the dim method) what the user provides. > > But no element space is needed in this case. If the "s" is never used in a form (as is the case in the mixed Poisson example), then it only needs to be evaluate-able. Hence, we should not require an element or function space to be set for Expressions. I seem to remember this being one of the main points with the Function vs Expression design. -- Marie > Johan > > > >> If no, then the behaviour is confusing. If >> yes, then that is not what I wanted to do above. >> >> >> -- >> Marie >> >> _______________________________________________ >> Mailing list: https://launchpad.net/~dolfin >> Post to : dolfin@lists.launchpad.net >> Unsubscribe : https://launchpad.net/~dolfin >> More help : https://help.launchpad.net/ListHelp >> _______________________________________________ Mailing list: https://launchpad.net/~dolfin Post to : dolfin@lists.launchpad.net Unsubscribe : https://launchpad.net/~dolfin More help : https://help.launchpad.net/ListHelp
