dolfin team mailing list archive

["Garth N. Wells" <g.n.wells@xxxxxxxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> On Fri, Oct 07, 2005 at 04:58:10PM +0200, Garth N. Wells wrote:
> 
> > Knowing the tensor rank and dimension of each field of a mixed formulation
> would
> > be useful for extracting "subfunctions".
> 
> You can access the list of elements that compose a mixed element
> through the member variable elements:
> 
> e0 = FiniteElement(...)
> e1 = FiniteElement(...)
> 
> element = e0 + e1
> 
> rank_0 = element.elements[0].rank()
> rank_1 = element.elements[1].rank()
> 
> But maybe you mean that you need this is information to be included in
> the generated code so it can be accessed in DOLFIN? We could do that,
> and it would make it possible to implement some more advanced
> functionality for the Function class in DOLFIN, like slicing out
> subfunctions:
> 
> Function w(...);
> Function u(w, 0, 2); // Components 0-1
> Function p(w, 2);    // Component 2
> 

This is exactly what I was thinking. It's now possible to take slices out of
vectors (without making a copy), so I now need to know how many components an
element has, etc. Also, it would be good to extract the relevant trial
functions. For example,

BilinearForm a;
FiniteElement element0 = a.trial(0);
FiniteElement element1 = a.trial(1);

Garth


> /Anders
> 
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