If u ( r ) were zero for all r – i.e., if the particles did not exert any influence on each other, then g ( r ) = 1 for all r and the mean local density would be equal to the mean density ρ ρ : the presence of a particle at O would not influence the particle distribution around it and the gas would be ideal. For distances r such that u ( r ) is significant, the mean local density will differ from the mean density ρ ρ , depending on the sign of u ( r ) (higher for negative interaction energy and lower for positive u ( r ) ).