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Re: [DOLFIN-dev] [Fwd: Re: [FEniCS-users] [Fwd: Re: tensor function]]

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Kristian Oelgaard wrote:

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?
yes i will try it out tonight when i have my mac where i have the current development versions of fenics, i just have a fixed release of fenics09 on my institute workstation 

thanks,
patrick



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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