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This chapter was automatically generated by an AI agent and has not been reviewed by a human. Read with caution.

Simulation Steps

The core logic of the model relies on user-defined states and their corresponding update functions. The model does not have a predefined set of states (e.g., susceptible, infected, recovered); the user establishes them. This provides flexibility, as models in epiworld can have an arbitrary set of states.

Discrete-Time Simulation

Like most other ABMs, epiworld simulates the evolution of a system in discrete steps. Each step represents a day in the system, and changes are reflected at the beginning of the following day. Therefore, agents can recover and transmit a virus on the same day.

Steps Within a Single Day

A single step of epiworld features the following procedures:

  1. State update — Agents are updated according to their current state. Each state has an associated update function that determines how agents in that state behave (e.g., whether they can infect others, recover, etc.).

  2. (Optional) Execute global events — A call to user-defined functions that affect the system as a whole. These can make any type of change in the system, such as implementing interventions, changing parameters, or collecting custom statistics.

  3. (Optional) Apply rewiring algorithm — When specified, the contact network is rewired according to a user-defined function. This can model changes in social behavior over time.

  4. Lock the results — The current date is incremented by one unit, and the changes (exposure, new infections, recoveries, etc.) are recorded in the database.

  5. (Optional) Mutate variants — When defined, viruses can mutate, with new variants appearing the next day.

Queuing System

To speed up computations, epiworld uses a queuing system that decides which agents will be active during each step and which will not. Agents are active when either they or at least one of their neighbors has an active virus. Updates are triggered only for agents in the queue, significantly accelerating each step—especially when most of the population is not near an infected individual.