The property of magnitudes that can be defined as follows. The value of a magnitude corresponding to a whole object is equal to the sum of the values of the magnitudes corresponding to its parts for any division of the object into parts. For instance, additivity of volume means that the volume of a whole object is equal to the sum of the volumes of its constituent parts. Cf. Additive function; Countably-additive set function.
Additivity. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Additivity&oldid=28135