An extra thermodynamic curiosity arises from the definition that memristors/memristive devices should energetically act like resistors. The instantaneous electrical power entering such a device is completely dissipated as Joule heat to the surrounding, so no extra energy remains in the system after it has been brought from one resistance state x i to another one x j. Thus, the internal energy of the memristor device in state x i, U (V, T, x i), would be the same as in state x j, U (V, T, x j), even though these different states would give rise to different device's resistances, which itself must be caused by physical alterations of the device's material.