Leveraging deep generative modelling at the agent level in discrete-event simulations
Emulators are often invoked to facilitate parameter inference in computationally intensive agent-based simulations (ABSs). Most approaches, however, require a large sample of pre-existing outputs on which such emulators can be trained. For computationally intensive simulations, this sample can be prohibitively expensive to generate. We propose a new approach to leverage emulators at the agent level in event-based ABSs to reduce the computational requirements of the simulation itself. We demonstrate this in a computationally intensive ``multi-disease'' ABS, Thanzi La Onse, which self-consistently simulates a wide range of medical conditions in a population. By applying conditional tabular generative adversarial networks to replace the modelling of one of the simulated causes of ill health, road traffic injuries (RTIs), we are able to improve its simulation run-time by 86.6% (95% bootstrap confidence interval [85.2, 88.1]), while recovering the evolution of cause-specific mean disability adjusted life years with a 13% error, despite the low assumed incidence of fatal RTIs (~2%). Crucially, we do so while retaining the full ABS framework, and correctly recovering multi-disease dynamics. This represents a crucial step towards enabling full-model emulators for very computationally intensive simulations, and making large ABS amenable to rigorous parameter inference and a full understanding of parameter sensitivity.