ffc team mailing list archive

[Kristian Oelgaard <k.b.oelgaard@xxxxxxxxxx>]

Quoting Anders Logg <logg@xxxxxxxxx>:

> On Thu, Oct 01, 2009 at 09:45:10AM +0200, Kristian Oelgaard wrote:
> > Quoting Patrick Riesen <priesen@xxxxxxxxxxxxxxx>:
> >
> > > i suppose the problem lies not in VTKFile.cpp.
> > >
> > > you consider a tensor function to have a rank >= 2,
> > > but for my tensor function the rank returned by e.g.
> > >
> > > e.function_space().element().value_rank()
> > >
> > > is 1. So it is rather a vector with 4 components having rank 1.
> > > possibly value_rank() in the FiniteElement class should return 2 even
> > > for a 2d tensor function, then your code in VTKFile is fine, but i
> > > didn't look into the FiniteElement classes.
> >
> > The problem is in ffc/fem/createelement.py where a tensor element is
> treated as
> > a MixedElement which has rank 1. A simple workaround might be to attach
> > len(ufl_element._shape) as the rank of a mixed element and use this value
> when
> > we generate code for the value_rank() function.
> > What do you think Anders?
>
> Feel free to try. Tensor functions are not very well supported at the
> moment anyway. This is something we'll need to look into at some point
> in the not so distant future. In particular, we're working on a solver
> for the bidomain equations where we will need tensor fields.
>
> It's not something I have time to look at just now though.

Neither do I, but I just added some code that should give the correct
value_rank() for tensor elements.
Patrick, could you try this out and report any problems related to vtk output?

Kristian

> --
> Anders
>
>
> > Kristian
> >
> > > patrick
> > >
> > >
> > > -------- Original Message --------
> > > Subject: Re: [FEniCS-users] [Fwd: Re:  tensor function]
> > > Date: Wed, 30 Sep 2009 11:30:45 +0200
> > > From: Patrick Riesen <priesen@xxxxxxxxxxxxxxx>
> > > CC: fenics <fenics-users@xxxxxxxxxx>
> > > References: <4AC31DB1.2040001@xxxxxxxxxxxxxxx>
> > > <4AC320F4.1000600@xxxxxxxxxxxxxxx> <4AC32181.8050202@xxxxxxxxx>
> > >
> > > seems that the tensor function for a 2d problem doesn't get to the
> > > output structure for a tensor function but to that for a vector function
> > > because it only has rank = 1. the write out for tensor is only invoked
> > > for a (3x3) tensor with rank = 2.
> > >
> > > Garth N. Wells wrote:
> > > >
> > > >
> > > > Patrick Riesen wrote:
> > > >> Hello,
> > > >>
> > > >> I don't know if this is a problem (dolfin0.9.2):
> > > >> When i was writing the TensorFunction e to a vtk-file after a solve
> > > >> by just using
> > > >>
> > > >> file << e
> > > >>
> > > >> the results i got were absolutely nonsense. I got three components,
> > > >> but none of them made any sense. This is why i was thinking i'm doing
> > > >> something completely wrong in my equations/code,
> > > >>
> > > >
> > > > VTK output of tensor functions is untested. I would be very surprised
> if
> > > > it did work. Dig around in VTKFile.cpp to see if you can find the
> problem.
> > > >
> > > > Garth
> > >
> > >
> > >
> > >
> > >
> > > >
> > > >> But if i first separate all components and write them to separate
> > > >> files as
> > > >>      Function e11 = e[0];
> > > >>      Function e12 = e[1];
> > > >>      Function e21 = e[2];
> > > >>      Function e22 = e[3];
> > > >>
> > > >>      fileE11 << e11;
> > > >>      fileE12 << e12;
> > > >>      fileE21 << e21;
> > > >>      fileE22 << e22;
> > > >>
> > > >> the solutions look reasonable (uff!..) and e12 and e21 are the same.
> > > >>
> > > >> regards,
> > > >> patrick
> > > >>
> > > >>
> > > >> Patrick Riesen wrote:
> > > >>> sorry, something went wrong, this would be the message:
> > > >>>
> > > >>> -------- Original Message --------
> > > >>> Subject: Re: [FEniCS-users] tensor function
> > > >>> Date: Wed, 30 Sep 2009 10:52:02 +0200
> > > >>> From: Patrick Riesen <priesen@xxxxxxxxxxxxxxx>
> > > >>> To: Anders Logg <logg@xxxxxxxxx>
> > > >>> References: <4AC0A8D5.6040207@xxxxxxxxxxxxxxx>
> > > >>> <20090928122033.GH2528@olorin>    <4AC0AD56.50608@xxxxxxxxxxxxxxx>
> > > >>> <20090928140134.GA24982@olorin> <4AC0C346.7020309@xxxxxxxxxxxxxxx>
> > > >>>
> > > >>> or maybe not..
> > > >>>
> > > >>> i can not do
> > > >>>
> > > >>> Function e11 = e[0][0];
> > > >>>
> > > >>> i get
> > > >>>
> > > >>> error: no match for 'operator[]' in
> > > >>> 'dolfin::Function::operator[](dolfin::uint)(0u)[0]'
> > > >>>
> > > >>>
> > > >>> but i can get components doing
> > > >>>
> > > >>> e11 = e[0];
> > > >>> e12 = e[1];
> > > >>> e21 = e[2];
> > > >>> e22 = e[3];
> > > >>>
> > > >>>
> > > >>> i suppose for dolfin 0.9.3 it is the case as described below and for
> > > >>> dolfin 0.9.2 the case as above therefore ?
> > > >>> (which is what i am still using currently)
> > > >>>
> > > >>> greetings,
> > > >>> patrick
> > > >>>
> > > >>> Patrick Riesen wrote:
> > > >>>> this helped to sort things out, thanks again.
> > > >>>> patrick
> > > >>>>
> > > >>>> Anders Logg wrote:
> > > >>>>> On Mon, Sep 28, 2009 at 02:34:30PM +0200, Patrick Riesen wrote:
> > > >>>>>> Hi,
> > > >>>>>>
> > > >>>>>> thans for the quick response,
> > > >>>>>>
> > > >>>>>> therefore when V is the function space of the (e, v, p) element
> and
> > > >>>>>>
> > > >>>>>>> e[0] = (a, b)
> > > >>>>>>> e[1] = (c, d)
> > > >>>>>>> e[0][0] = a
> > > >>>>>>> e[0][1] = b
> > > >>>>>>> e[1][0] = c
> > > >>>>>>> e[1][1] = d
> > > >>>>>> therefore doing
> > > >>>>>>
> > > >>>>>> fs = new SubSpace(V,0,0)
> > > >>>>>>
> > > >>>>>> corresponds to the subspace for the two components (a, b) of the
> > > >>>>>> element  and not just for a, which then would be SubSpace(V,0,0,0)
> ?
> > > >>>>> Yes.
> > > >>>>>
> > > >>>> _______________________________________________
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> > > >>>
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