Anders Logg wrote:
> On Mon, Oct 19, 2009 at 12:21:36PM +0100, Garth N. Wells wrote:
>>
>> Anders Logg wrote:
>>> On Sat, Oct 17, 2009 at 05:41:54PM +0100, Garth N. Wells wrote:
>>>> Anders Logg wrote:
>>>>> On Sat, Oct 17, 2009 at 01:54:57PM +0100, Garth N. Wells wrote:
>>>>>> Johan Hake wrote:
>>>>>>> On Saturday 17 October 2009 12:32:54 Garth N. Wells wrote:
>>>>>>>> Will
>>>>>>>>
>>>>>>>> uh = U[1]
>>>>>>>>
>>>>>>>> return a deep or shallow copy of the sub-Function?
>>>>>>> To avoid confusion with the ufl interface we have limited the interface
>>>>>>> for
>>>>>>> SubFunctions in PyDOLFIN to split. split returns a shallow copy by
>>>>>>> default.
>>>>>>> pass True to split and it will return a deepcopy. In your case it would
>>>>>>> be:
>>>>>>>
>>>>>>> uh = U.split()[0]
>>>>>>>
>>>>>>> and
>>>>>>>
>>>>>>> uh = U.split(True)[0]
>>>>>>>
>>>>>>> operator[] is used when you define forms. We have not yet managed to
>>>>>>> merge the
>>>>>>> two operations into one.
>>>>>>>
>>>>>> OK. Do we still have the function 'sub'?
>>>>>>
>>>>>>
>>>>>>>> Where is the operator [] define for sub-Functions?
>>>>>>> The operator you are using is the ufl one, which is defined in
>>>>>>> ufl.exproperators.py.
>>>>>>>
>>>>>> OK, but it's not clear to me then what's happing with this extract of my
>>>>>> code:
>>>>>>
>>>>>> problem = VariationalProblem(a, L, bcs)
>>>>>> Uh = problem.solve()
>>>>>>
>>>>>> u = Expression("epx(x[0])", V = Vexact)
>>>>>>
>>>>>> uh = Uh[1]
>>>>>> M = (uh-u)*(uh-u)*dx
>>>>>> error = sqrt(assemble(M, mesh=mesh))
>>>>> This should work fine since uh will be a component of the coefficient
>>>>> Uh in the UFL form.
>>>>>
>>>>> Same as when you write say inner(v, u)*dx or anything else that
>>>>> accesses components.
>>>>>
>>>>> So in summary [] can be used for any purpose in forms. It can also be
>>>>> used for plotting, but extracting the vector etc will not work.
>>>>>
>>>> It works as expected, but what's going on behind the scenes? Who is
>>>> creating the dof map and is the vector being copied?
>>> There's nothing out of the ordinary going on behind the scenes.
>>>
>> There must be something going on - either a reference to or a copy of
>> the underlying vector, and a dof map. Where are these coming from?
>
> Why must there be a reference? Are we discussing different things
> here?
>
This is what I'm doing/want to know:
# Compute Uh
Uh = my_pde.solve()
# Get sub-function. uh is both a UFL and a cpp Function. What's
# happening on the cpp side here?
uh = Uh[1]
Garth
> --
> Anders
>
>
>> Garth
>>
>>> When you write
>>>
>>> uh = Uh[1]
>>>
>>> it's no different from doing
>>>
>>> a = uh[1]*v*dx
>>>
>>> or doing
>>>
>>> gradu = grad(u)
>>> a = dot(grad(v), gradu)*dx
>>>
>>> gradu is not a new Function, it's a UFL expression involving the grad
>>> operator and the Function u. gradu can be used in forms and plotted
>>> (since the plot will project it to a Function), but you can't do
>>> gradu.vector().
>>>
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