In human thermodynamics, inverse entropy refers to activities, such as the male praying mantis willing allowing his mate to eat him during copulation or insects that mimic braches, or the cleric’s act of self-abnegation, that produce the effect of negative entropy. [1] In pure formulation this would be:

although, it is difficult to say if this makes any formulaic sense.
In 1973, French sociological anthropologist Roger Caillois, in his The Dissymmetry, supposedly, introduced the term "inverse entropy" as a theoretical concept. [2]
References
1. Hollier, Denis and Porter, Catherine. (1997). Absent Without Leave: French Literature under the Threat of War (pgs. 41-42, etc, 200). Harvard University Press.
2. Caillois, La dissymetrie (1973), in Coherences Aventureuses (Paris: Gallimard, 1976), pg. 268.