I found this problem in my own program. Here is the test code example:
int main(int argc, char** argv)
{
LibMeshInit init(argc, argv);
UnstructuredMesh *mesh;
ExodusII_IO *exio;
EquationSystems *eqsys;
System *asys;
libMesh::PointLocatorTree *locator;
mesh = new Mesh(init.comm());
exio = new ExodusII_IO(*mesh);
locator = new PointLocatorTree(*mesh);
exio->read("res.e");
mesh->allow_renumbering(false);
mesh->prepare_for_use();
float pt[3] = {0, 0, 0};
for (int i=0; i<20; i++)
{
Point p(pt[0]+(float)i/100., pt[1]+(float)i/100., pt[2]+(float)i/100.);
const Elem *e = (*locator)(p); // it takes much time (at least 1s or even
100s)
if (e != NULL) fprintf(stderr, "point locate cell: %d\n", e->id());
else fprintf(stderr, "locate NULL\n");
}
return 0;
}
I just selected 20 points and located the cells they were in. The locator took
much time every time.
The points can be found in elements when executing. But when enabling
_out_of_mesh_mode, the elements can not be located.
So It seems that the locator always falls into perform_linear_search
<http://libmesh.github.io/doxygen/classlibMesh_1_1PointLocatorTree.html#acd313428c9a4551d7e1aaa141e7ae8e7>
function when executing operator()
<http://libmesh.github.io/doxygen/classlibMesh_1_1PointLocatorTree.html#a08990e437871fc26e3043806aef8dfaa>.
> On Jun 23, 2016, at 5:42 PM, John Peterson <[email protected]> wrote:
>
>
>
> On Thu, Jun 23, 2016 at 4:23 PM, 张江 <[email protected]
> <mailto:[email protected]>> wrote:
> Hi,
>
> I am using libmesh to read a large unstructured grid data. The mesh info is
> below:
>
> Mesh Information:
> elem_dimensions()={3}
> spatial_dimension()=1
> n_nodes()=67855938
> n_local_nodes()=0
> n_elem()=181423412
> n_local_elem()=0
> n_active_elem()=181423412
> n_subdomains()=0
> n_partitions()=1
> n_processors()=1
> n_threads()=1
> processor_id()=0
>
> I found that when locating a point by PointLocatorTree, it always took much
> time (about 50s or even more).
>
> How many points did you look for? The cost to initially build the
> PointLocator is expensive, but it's amortized by the fact that you can use it
> multiple times once it's built...
>
>
> It seems that the locator always falls into perform_linear_search
> <http://libmesh.github.io/doxygen/classlibMesh_1_1PointLocatorTree.html#acd313428c9a4551d7e1aaa141e7ae8e7
>
> <http://libmesh.github.io/doxygen/classlibMesh_1_1PointLocatorTree.html#acd313428c9a4551d7e1aaa141e7ae8e7>>
> function when executing operator()
>
> It "seems"? The linear search should only happen if the point fails to be
> found. If the point is not being found in any element, you should look into
> why that happens first...
>
> --
> John
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