# possible bug with 1D high-order Lagrange element

**URL:** https://discourse.paraview.org/t/possible-bug-with-1d-high-order-lagrange-element/3396
**Category:** ParaView Support
**Tags:** high-order-elements
**Created:** [January 24, 2020, 10:49am UTC](https://discourse.paraview.org/t/possible-bug-with-1d-high-order-lagrange-element/3396 "2020-01-24T10:49:23Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![saramito](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@saramito](https://discourse.paraview.org/u/saramito)
#### Post date: [January 24, 2020, 10:49am UTC](https://discourse.paraview.org/t/possible-bug-with-1d-high-order-lagrange-element/3396/1 "2020-01-24T10:49:24Z")

</div>

Dear Paraview developers,

I have a mistake with the high-order Lagrange 1D element :  
VTK\_LAGRANGE\_CURVE = 68 in vtkCellType.h  
I use the 5.7.0 version of paraview ?

I combine this high-order 1D element with the Tessellate filter  
in order to represent a piecewise polynomial 1D curve  
in a 2D space or 3D space.

Please find in attachment some snapshots .jpg together  
with the .vtk file of what I obtained: results are unexpected.  
In comparison, results are right with both  
VTK\_QUADRATIC\_EDGE = 21  
VTK\_CUBIC\_LINE = 35

Please could you explain me if there is a mistake with this example ?  
Otherwise, if there is a bug with 1D high-order Lagrange element,  
could you please suggest me a way to circumvent it  
with my 5.7.0 version of paraview ?

I use paraview as post-processor of the Rheolef FEM C++ library :  
[https://www-ljk.imag.fr/membres/Pierre.Saramito/rheolef](https://www-ljk.imag.fr/membres/Pierre.Saramito/rheolef)  
This library supports intensively high-order elements.

Many thanks for your very nice code and your help,

Pierre

---

<div class="post-metadata">

### Author: ![saramito](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/s/f17d59/32.png) [@saramito](https://discourse.paraview.org/u/saramito)
#### Post date: [January 24, 2020, 10:58am UTC](https://discourse.paraview.org/t/possible-bug-with-1d-high-order-lagrange-element/3396/2 "2020-01-24T10:58:45Z")

</div>

Sorry, but the attached files was missing in my previous message:  
here is a link to download them:  
[https://www-ljk.imag.fr/membres/Pierre.Saramito/tmp/lagrange-curve-bug.zip](https://www-ljk.imag.fr/membres/Pierre.Saramito/tmp/lagrange-curve-bug.zip)

There are .jpg snapshots and .vtk files for:

- Lagrange 4th order element
- Cubic element
- Quadratic element

Only the Lagrange high-order behaves badly, others are ok;  
Thanks by advance for your response,

Pierre