Compartment Models

17 Jul 2022 15:00

Yet Another Inadequate Placeholder

A "compartment model" is a model for the evolution of a population. At any give time, each individual in the population is of one of a finite number of types. That is, the population is divided up among "compartments", one compartment per type. Individuals can "transition" from one compartment to another, i.e., change types. (In some versions, individuals can also be born and die.) The rates at which they make these transitions are allowed to be functions of the current distribution of the population across compartments; sometimes we allow for the history of the distribution to matter as well. There are deterministic and stochastic versions; I am particularly interested in stochastic versions which approach deterministic limits as the population size grows.

These get used a lot as models of contagious disease (where the compartments are status like "infectious", "exposed but not yet infectious", "recovered", etc.), and in demography (where the compartments are things like "Male 18--22" or "Female 90--94", perhaps further sub-divided by marital status, caste, etc.) They are also formally identical to models in chemical kinetics and physical chemistry, which was the inspiration for one of the pioneers here, A. J. Lotka.

See also: Branching Processes; Convergence of Stochastic Processes; Demography; Epidemic Models; Markov Models; Mean-Field Games and Mean-Field Control