Is extensivity a fundamental property of entropy?
Stephen R. Addison, John Edward Gray · Journal of Physics A Mathematical and General · 2001
The role of linearity in the definition of entropy is examined. While discussions of entropy often treat extensivity as one of its fundamental properties, the extensivity of entropy is not axiomatic in thermodynamics. It is shown that systems in which entropy is an extensive quantity are systems in which a entropy obeys a generalized principle of linear superposition.