function mass_balance = check_mass_balance(t, initial_fluid_mass, rho, is_fluid)

%%%%    This function checks to see if the total fluid mass in a lattice
%%%%    Boltzmann simulation is within 10% of the initial fluid mass.  If
%%%%    the code is running properly, then the fluid mass should not change
%%%%    over time.  Sometimes, depending on the boundary conditions
%%%%    employed, there might be slight changes in the fluid mass
%%%%    (compressibility effects).  If the fluid mass is within 10% of its
%%%%    initial value, then a value of TRUE is returned for the boolean
%%%%    variable mass_balance.  If the fluid mass is not within 10% of its
%%%%    initial value, then a value of FALSE is returned.

    mass_balance = true;
    
    total_fluid_mass = sum(sum(  is_fluid .* rho  ));
    display([t total_fluid_mass]);
    
    if ((total_fluid_mass > 1.1*initial_fluid_mass) || (total_fluid_mass < 0.9*initial_fluid_mass))
        mass_balance = false;
    end
        
end