# Is particle mass always constant？

In the wiki 3.3 section it reads:

Throughout the duration of a weakly-compressible SPH simulation (as presented herein)** the mass of each particle remains constant** and only their associated density fluctuates.

I wonder whether this is also true for any formulation applied in DualSPHysics (for example, also in Non-Newtonian solver using "constitutive eq formulation")? Based on my understanding, the mass of each particle is determined at the initial state and remained constant through of the computing and is the same with all other particles.

I also checked the "run.out" file, it always gives:

massfluid = aaaa;

massbound = aaaa;

Looks like aaaa is not a function of time and particle id.

Thanks!