Thank you again for your help!
In the line 353 of dynamics.hh, the pressure is calculated as p = rho / invCs2, which is calculated as I expect.
However, in the line 450 of util.h, the lattice pressure is calculated by p = (rho-1) * Cs2.
The difference between rho and rho-1 comes from the difference between pressure and lattice pressure?
Then, is there any reason that the lattice pressure is defined by using the factor of rho-1 instead of rho?