[Paraview] Quadrangles and Q_1,1 basis functions

[Torquil Macdonald Sørensen]

Hi!

Thank you very much for the suggestion, but in that case I seem to end
up with a function that is constant within each square in the mesh.

A general Q_1,1 function can have different values in each of the four
corners of each square, and in the interior it is a first order
polynomial w.r.t. each of the variables x and y.

Does Paraview support the display of such a function which is not
necessarily constant within each square?

Best regards,
Torquil Sørensen

On 23/09/15 10:15, Kaushik Kulkarni wrote:
> Hey Torquil Sørensen,
> You will get the desired solution once you change "POINT_DATA 9" to
> "CELL_DATA 4".
> And then similarly specifying the data in each of the cell. In this case
> I suppose the .vtk file for you should be-
> 
> 
> # vtk DataFile Version 2.0
> Exported by getfem++
> ASCII
> DATASET UNSTRUCTURED_GRID
> POINTS 9 float
>  0 0 0
>  0.5 0 0
>  0 0.5 0
>  0.5 0.5 0
>  1 0 0
>  1 0.5 0
>  0 1 0
>  0.5 1 0
>  1 1 0
> 
> CELLS 4 20
>  4 0 1 3 2
>  4 1 4 5 3
>  4 2 3 7 6
>  4 3 5 8 7
> 
> CELL_TYPES 4
>  9
>  9
>  9
>  9
> 
> CELL_DATA 4
> 
> 
> SCALARS scalarField float 1
> LOOKUP_TABLE default
>  0 0 0 1
> 
> Cheers,
> Kaushik
> 
> 
> 
> On Tue, Sep 22, 2015 at 7:56 PM, Torquil Macdonald Sørensen
> <torquil at gmail.com <mailto:torquil at gmail.com>> wrote:
> 
>     Hi!
> 
>     I have defined a 2d quadrangle mesh consisting of 2x2 elements, with
>     Q_1,1 basis functions in GetFEM++, and exported an example function to
>     ASCII VTK format. The only node at which the example function is nonzero
>     is the middle one.
> 
>     When I open the VTK file in Paraview, it looks as if it has used some
>     kind of triangle interpolation. Instead of its support being the entire
>     mesh, it has become zero near two opposite domain corners. In
>     particular, the result should have been 90-degree rotation symmetric
>     about the centre node.
> 
>     How do I get Paraview to display this Q_1,1 function correctly, or at
>     least without it seemingly being interpolated onto a triangular mesh?
> 
>     I'm using Paraview 4.3.1 and the ASCI VTK file generated by GetFEM++ is:
> 
>     # vtk DataFile Version 2.0
>     Exported by getfem++
>     ASCII
>     DATASET UNSTRUCTURED_GRID
>     POINTS 9 float
>      0 0 0
>      0.5 0 0
>      0 0.5 0
>      0.5 0.5 0
>      1 0 0
>      1 0.5 0
>      0 1 0
>      0.5 1 0
>      1 1 0
> 
>     CELLS 4 20
>      4 0 1 3 2
>      4 1 4 5 3
>      4 2 3 7 6
>      4 3 5 8 7
> 
>     CELL_TYPES 4
>      9
>      9
>      9
>      9
> 
>     POINT_DATA 9
> 
> 
>     SCALARS scalarField float 1
>     LOOKUP_TABLE default
>      0 0 0 1 0 0 0 0 0
> 
>     Thanks and best regards
>     Torquil Sørensen
> 
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