ufl team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Tue, Mar 3, 2009 at 6:50 PM, Kristian Oelgaard
<k.b.oelgaard@xxxxxxxxxx> wrote:
> Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:
>
>> On Tue, Mar 3, 2009 at 6:29 PM, Kristian Oelgaard
>> <k.b.oelgaard@xxxxxxxxxx> wrote:
>> > Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:
>> >
>> >> On Tue, Mar 3, 2009 at 4:37 PM, Kristian Oelgaard
>> >> <k.b.oelgaard@xxxxxxxxxx> wrote:
>> >> > Quoting Martin Sandve Alnæs <martinal@xxxxxxxxx>:
>> >> >
>> >> >> Nothing implemented, no.
>> >> >> I'll have to think about it.
>> >> >>
>> >> >> Martin
>> >> >
>> >> > Could someone please fill me in on the most important details of
>> >> ListTensor?
>> >> > Looking at the sub tree I get a strong urge to just ignoring it, would
>> that
>> >> be safe?
>> >> >
>> >> > Kristian
>> >>
>> >> I don't get what you're asking for here. Temporarily you can
>> >> probably ignore it, but in the end it should be supported.
>> >
>> > I had a second look at Indexed vs. ComponentTensor (and ListTensor) and I
>> think
>> > I managed to make some sense out of it. But why does ListTensor not have
>> indices
>> > like ComponentTensor?
>> >
>> > Kristian
>>
>> Why should it have indices? It represents a tensor composed of an
>> explicit list of arbitrary subtensors with no connection whatsoever.
>> (If its subtensors are scalar expressions, think of it as ListVector,
>> which it was in the first version)
>>
>> Example:
>>   w = as_vector((1.0, 2.0)) # -> ListTensor((FloatValue(1.0),
>> FloatValue(2.0))
>>   fixed_convection = dot(w, grad(u))
>
> Maybe it's just because I don't see what ListTensor does which ComponentTensor
> can't.
>
> Kristian

For starters, ComponentTensor can't represent the constant vector
(1.0, 2.0) shown above.

Take a scalar expression Aij with A.free_indices() being
a superset of all indices in the MultiIndex ij, and let
  A = ComponentTensor(Aij, ij)
Here A represents the tensor-valued expression with components given by Aij.
The rank of A equals len(ij).

Then assume (a, b, c) three distinct unrelated scalar expressions, and let
  B = ListTensor(a, b, c)
Here B represents the vector with components a, b, and c.

Martin