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?
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().
>
> --
> Anders
>
>
> ------------------------------------------------------------------------
>
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@fenics.org
> http://www.fenics.org/mailman/listinfo/dolfin-dev
_______________________________________________
DOLFIN-dev mailing list
DOLFIN-dev@fenics.org
http://www.fenics.org/mailman/listinfo/dolfin-dev
