Bug with MeshValueCollection (v 2019.2.dev0)?

Errors
1

Hi all,
I wanted to report a bug with the MeshValueCollection function.

I was trying to read cell data from the input mesh that marks a domain initially using:

mesh_file = XDMFFile(MESH_FILE_NAME)
mesh = Mesh()
mesh_file.read(mesh)

Dim = mesh.topology().dim()
MATID = MeshValueCollection("size_t", mesh, Dim)
mesh_file.read(MATID, "Mat ID")
domainMarks = MeshFunction("size_t", mesh, MATID) 
domainMarks.rename("Mat ID","label")

But somehow the MeshValueCollection a value that was originally for example 3, when read becomes 2.

I dug a bit deeper, and when I used “double” in the MeshValueCollection, 3 was read as 2.99999995 and when using “size_t” or “int”, it rounded it to 2.

So now instead of the above code I am using the following:

mesh_file = XDMFFile(MESH_FILE_NAME)
mesh = Mesh()
mesh_file.read(mesh)

Dim = mesh.topology().dim()
MATID = MeshValueCollection("double", mesh, Dim)
MATID_int = MeshValueCollection("size_t", mesh, Dim)
mesh_file.read(MATID, "Mat ID")
mesh_file.read(MATID_int, "Mat ID")
for ii in range(MATID.size()):
	MATID_int.set_value(ii,0,round(MATID.get_value(ii,0)))
domainMarks = MeshFunction("size_t", mesh, MATID_int) 
domainMarks.rename("Mat ID","label")

I am using 2019.2.dev0 version. I am not sure if the function exists or was fixed in DolfinX.

2

Without having the file that you are reading, it is hard to do anything further with this. To me it Seems like you are trying to read something that has a different datastyre (dtype) than you are trying to read in.

In DOLFINx MeshValueCollection has been replaced with MeshTags. It is a new implementation, so it is unlikely that a similar bug would be present (if it indeed is a bug).

3

Hi Dokken,

I am attaching a sample mesh using which this bug can be noticed. It is a 4x4x4 cube with 3 subdomains.

I wanted to report in case someone is using the same method I am using and may not have seen this issue. I am not sure if it could be a problem with the build I am using.

Best regards,