[EMAIL PROTECTED] wrote:
>> On Thu, Sep 11, 2008 at 07:35:30PM +0100, Garth N. Wells wrote:
>>>
>>> Anders Logg wrote:
>>>> On Thu, Sep 11, 2008 at 03:59:18PM +0100, Garth N. Wells wrote:
>>>>> Anders Logg wrote:
>>>>>> On Thu, Sep 11, 2008 at 03:02:36PM +0100, Garth N. Wells wrote:
>>>>>>> Anders Logg wrote:
>>>>>>>> On Thu, Sep 11, 2008 at 02:51:41PM +0100, Garth N. Wells wrote:
>>>>>>>>> Martin Sandve Alnæs wrote:
>>>>>>>>>> I don't agree, isn't the point that several DiscreteFunctions
>>> can
>>>>>>>>>> share a FunctionSpace?
>>>>>>>>>>
>>>>>>>>> Yes, but a dof map doesn't define a function space.
>>>>>>>>>
>>>>>>>>> Garth
>>>>>>>> I think the dof map should be in the FunctionSpace, that way
>>> several
>>>>>>>> functions may share the dof map (which may take time to compute if
>>> we
>>>>>>>> want to do some reordering).
>>>>>>>>
>>>>>>>> Two functions in the same function space share the mesh, the
>>> element
>>>>>>>> and the dof map (these three define the space) but each function
>>> has
>>>>>>>> its own vector.
>>>>>>>>
>>>>>>> My point isn't that a DofMap won't shared, it's that it's not part
>>> of
>>>>>>> the definition of a function space.
>>>>>> It is part of the function space if we say that a function space is
>>>>>> defined by a particular basis:
>>>>>>
>>>>>> V = span{\phi_i}
>>>>>>
>>>>>> To define the basis, we need the dof map.
>>>>>>
>>>>> The dof map is needed to tie the finite element basis + domain (mesh)
>>> to
>>>>> a matrix/vector.
>>>> Not only that. It's needed to define the global function space. If we
>>>> just have the elements, we don't know the function space. P_k and DG_k
>>>> have the same finite element, but different dof maps.
>>> The definitions of P_k and DG_k are what define the space.
>>>
>>>>>>> It always possible that two discrete functions which are equivalent
>>> can
>>>>>>> share a mesh and finite element (which defines the function space),
>>> but
>>>>>>> have different vectors and dof maps.
>>>>>> Is that something we will encounter much?
>>>>> Probably not, but it shows why the dof map doesn't belong in
>>> FunctionSpace.
>>>>> On reflection, FunctionSpace is pretty simple, so I don't actually
>>> see
>>>>> why we need it. If we want to stress that a group of objects belong
>>>>> together in the definition of a discrete function, why not just use a
>>>>> tuple in DiscreteFunction?
>>>> We've discussed before that we want to reuse dof maps and share them
>>>> between elements. It would be convenient to include the dof map in a
>>>> function space and then we only need to worry about one thing that is
>>>> shared between functions, namely the function space. This seems very
>>>> natural: one function space V and many functions v, u, w in V.
>>>>
>>> I agree that it's natural group whatever defines the space, but I'm
>>> raising the question should a class FunctionSpace or a tuple be used,
>>> e.g.
>>>
>>> tuple<Mesh*, FiniteElement*, DofMap*> function_space;
>>>
>>> or
>>>
>>> typedef tuple<Mesh*, FiniteElement*, DofMap*> FunctionSpace;
>>> FunctionSpace function_space;
>>>
>>> Garth
>> I guess it can be useful to have it as a class if we want to attach
>> something else, like boundary conditions. A FunctionSpace could be the
>> above three things, and then a set of constraints. But I don't know
>> exactly how this would fit in with the assembly since we apply bcs to
>> the whole system.
>>
>> Having a FunctionSpace class might simplify things like eliminating
>> dofs (and putting them back in again).
>>
>> --
>> Anders
>
> Agree. If we are to employ negative indices on bc this could be a way to
> do it.
>
> Is the name FunctionSpace the best? I mean also a finite element is a
> function space.
>
> But I think the structure is handy.
>
Agree. I'm for the structure, but I'd like to kick around some names.
Garth
> Kent
>
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