I convert my msh file to xml using the dolfin-convert instruction. I have a doubt, Why this instruction create two files, one of them called name_physical_region.xml and the other name.xml?, whats is the reason to create the name_physical_region.xml file?.
If you have marked some of your subdomains and boundaries (For example in GMSH), after converting your mesh with dolfin-convert, 3 files will be created including: