Non-Additive Entropy Formulas: Motivation and Derivations.

Entropy is a great tool in thermodynamics and statistical physics. This Special Issue is devoted to the mathematical background and physical motivation behind using non-additive entropy formulas, which are, in most cases, still group entropies, defined as expectation values, and incorporate, in one way or another, nontrivial correlations in the investigated systems and processes. The concept of entropy has been changing swiftly since C. Tsallis and, before him, a series of mathematicians and informatics experts proposed various generalizations of Boltzmann-Gibbs entropy. [Extracted from the article]