dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

Anders Logg wrote:
> On Mon, Feb 15, 2010 at 11:39:26AM +0100, Marie Rognes wrote:
>> Garth N. Wells wrote:
>>> Anders Logg wrote:
>>>> On Fri, Feb 12, 2010 at 05:42:26PM +0000, Garth N. Wells wrote:
>>>>> Anders Logg wrote:
>>>>>> On Fri, Feb 12, 2010 at 04:57:05PM +0100, Anders Logg wrote:
>>>>>>> On Fri, Feb 12, 2010 at 04:23:51PM +0100, Marie Rognes wrote:
>>>>>>>> I'm interesting in accessing the vector of a Function after mesh-refinement.
>>>>>>>> At the moment, I'm getting:
>>>>>>>>
>>>>>>>>   RuntimeError: *** Error: You are attempting to access a non-const
>>>>>>>>   vector from a sub-Function.
>>>>>>>>
>>>>>>>> Is this inevitable, a bug or a trigger-happy error message?
>>>>>>>>
>>>>>>>>   from dolfin import *
>>>>>>>>   mesh = UnitSquare(2,2)
>>>>>>>>   V = FunctionSpace(mesh, "CG", 1)
>>>>>>>>   u = Function(V)
>>>>>>>>   mesh.refine()
>>>>>>>>   u.vector()
>>>>>>> Looks like a bug. The function is not being refined but the mesh, the
>>>>>>> dofmap and the functionspace is refined. Might be related to the
>>>>>>> recent work on refinement.
>>>>>> It should be fixed now. Someone had commented out register_object in
>>>>>> the Function constructor.
>>>>> I'm not too keen on all this magic. Harish I and have an adaptive solver
>>>>> in which the function spaces are declared inside a loop and it's slowly
>>>>> leaking memory, but I can't figure out why. 'Magic' makes it really hard
>>>>> to figure out what's going on.
>>>> That's unfortunate. But the magic is necessary if we should allow
>>>> meshes to be refined. The other option would be to remove
>>>> mesh.refine() and always rely on
>>>>
>>>>  new_mesh = refine(mesh)
>>>>
>>>> And then explicitly create the new function spaces and project the
>>>> functions.
>>>>
>>> This is what we're doing.
>>>
>>> Garth
>>>
>>>
>>>> I'm not sure which implications that would have fore Marie's code.
>>>> Marie?
>>>>
>> I'm pretty keen on the magic, but can survive without it.
> 
> I also like the magic, but AdaptiveObjects.cpp is complex and fragile
> so it would be good to remove it.
>

What about a free-function or a like 'adapt', or a class with static
member functions, that takes multiple arguments? It could be passed a
MeshFunction of cells to refine/coarsen, and from the Python side you
could even pass the function with which you want to adapt the mesh.

We could also keep AdaptiveObjects, but have users register functions
manually.

Garth

>> If the automagic updating of function spaces etc is removed.
>> then mesh.refine() should definitely be disabled.
>
> Yes, definitely.
> 
> But let's keep AdaptiveObjects until we have ported our code to
> 
>   new_mesh = refine(mesh)
> 
> --
> Anders