At the annual meeting of the Association for the Advancement of Artificial Intelligence (AAAI) this month, MIT researchers will present algorithms that represent significant steps toward “a better Siri” — the user-assistance application found in Apple products.

One aspect of the software that distinguishes it from previous planning systems is that it assesses risk.

"It’s always hard working directly with probabilities, because they always add complexity to your computations,” said Cheng Fang, a graduate student in MIT’s Department of Aeronautics and Astronautics. “So we added this idea of risk allocation. We say, ‘What’s your budget of risk for this entire mission? Let’s divide that up and use it as a resource.’”

The time it takes to traverse any mile of a bus route, for instance, can be represented by a probability distribution — a bell curve, plotting time against probability. Keeping track of all those probabilities and compounding them for every mile of the route would yield a huge computation. But if the system knows in advance that the planner can tolerate a certain amount of failure, it can, in effect, assign that failure to the lowest-probability outcomes in the distributions, lopping off their tails. That makes them much easier to deal with mathematically.


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