  Inspired by the epidemic contact tracing technique, we propose a method to
efficiently solve electromagnetics by tracing the energy distribution. The
computational domain is adaptively decomposed, and the available computational
resources are focused on those energy-active (infections) and their adjacent
(exposed) domains, while avoiding the unnecessary computation of energy-null
(unexposed) domains. As an example, we employ this method to solve several
optics problems. The proposed method shows high efficiency while maintaining a
good accuracy. The energy tracing method is based on the causality principle,
and therefore is potentially transformative into other computational physics
and associated algorithms.
