A "digital twin" is a online mathematical model/function/simulation that is continuously fed with sensor input data.<p>It's a new term for an old idea that has been around for decades in manufacturing; but what's old is new again in the context of IoT devices.<p>And it's only the first step -- manufacturing has gone a few steps farther.<p>Digital twins are primarily concerned with constructing a digital <i>representation</i> of a physical process/asset.<p>Model-based predictive control [1] (developed in 1980) has been used commercially to not only automatically control said assets, but do so optimally (by iteratively solving an optimization problem based on a mathematical model at every time period, and then reading new measurements off the feedback loop to update itself).<p>This type of optimal control technology is the reason why oil refineries are run so efficiently today.<p>[1] <a href="https://en.wikipedia.org/wiki/Model_predictive_control" rel="nofollow">https://en.wikipedia.org/wiki/Model_predictive_control</a>