Program 3.4 implement an SEIR model with four age-classes and yearly aging, closely matching the implications of grouping individuals into school cohorts. The four age-classes modelled are 0-6, 6-10, 10-20 and 20+ years old. Key to this model are two basic assumptions:
Only individuals in the adult class give birth, and only individuals in the adult class die.
Births and deaths are continuous, but aging only happens once per year.