[Gmsh] create partitions

[david free]

Hello,
I discovered gmsh and tried to make use it for my students and collegues 
since two years. I'm using gmsh with a multiscale solver written in C++. 
Until nom I assigned physical entities for each sub-domains and 
interfaces that I wanted and created manually a file containing a tag 
for materials.
I read tutorials and I saw that in the 2.0 version of the msh files, it 
is possible to use partition and sort it in the msh file. Using these 
partitions should be very interestiong for me because I will apply 
physical entities for materials and partitions for sub-domains.
Can you explain me how to create these partitions in the gmsh.1.61.0 
version under linux.
Thank you very much for your help