Dear developers,
I am trying out the VTK Input-Output feature of libmesh and run in
a bug that causes incorrect output of refined meshes.
In the following test code I create a mesh of a single QUAD4 element and
call vtkio.write to output the mesh into a file. The output is correct,
since the mesh has 4 nodes and the element (0123).
Next, I repeatedly uniformly refine the mesh and call vtkio.write again.
Already after 1 refinement, the output is wrong: the output file
correctly contains 4 elements, but the inactive (0123) is included,
while the active top-right subelement (5728) is not included. (At this
point, viewing the file with paraview, it has a reasonable look, but
after another refinement, the problem becomes evident even at visual
inspection)
I had a quick look at the code and maybe the bug is in
libMesh::VTKIO::cells_to_vtk (at line 140 of file vtk_io.C).
In fact, I think that the loop
for(unsigned int el_nr =0; el_nr< mesh.n_active_elem(); ++el_nr){
Elem *elem = mesh.elem(el_nr);
loops over the first n_active_elem(), regardless of their state, while
it should loop only over active elements.
By the way, also vtkio.write_equation_systems has some funny behaviour,
but hopefully it's the same bug...
I hope this helps. The code to reproduce the bug follows the signature.
(For the records, I have libmesh-0.7.0.4, compiled with VTK support and
using vtk5.4 libraries on a Debian squeeze system)
Best regards,
Matteo Semplice
=================== vtk_output_error.C =================
// C++ include files that we need
#include <iostream>
// Functions to initialize the library.
#include "libmesh.h"
// Basic include files needed for the mesh functionality.
#include "mesh.h"
// Include file that defines various mesh generation utilities
#include "mesh_generation.h"
#include "mesh_refinement.h"
//Include VTK Input-Output
#include "vtk_io.h"
// Bring in everything from the libMesh namespace
using namespace libMesh;
int main (int argc, char** argv)
{
LibMeshInit init (argc, argv);
// Skip this 2D example if libMesh was compiled as 1D-only.
libmesh_example_assert(2 <= LIBMESH_DIM, "2D support");
// Create a mesh
Mesh mesh;
// A mesh with just 1 QUAD4 element
MeshTools::Generation::build_square (mesh, 1, 1, 0.,1.,0.,1.,QUAD4);
VTKIO vtkio(mesh);
MeshRefinement mesh_ref(mesh);
for (int ref=0;ref<5;ref++)
{
if (ref>0){
mesh_ref.uniformly_refine(1);
}
std::ostringstream filename;
filename << "mesh"<<ref<<".vtu";
vtkio.write(filename.str());
}
return 0;
}
====================================================
--
Matteo Semplice Dip. di Fisica e Matematica
Phone: 031-2386132 Università dell'Insubria
Fax: 031-2386209 Via Valleggio, 11
22100 Como
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