$physicalgroup

Format:

$physicalgroup
physical group number

Example:

$physicalgroup
1  
2  
3  
4  
5  
6  
7  
8  
9  
10  

This corresponds to GMSH physical group. If you set physical group, here will shows the group number. If you didn't set any group, there will appears the number of physical group as the same as the number of layers.