“My research pulls together economics, computer science & management"

Andrés Cristi can’t resist the challenge of finding the missing piece of the puzzle. That drive helped prompt him to study engineering – and especially mathematics. Today a tenure-track assistant professor, Cristi explains that “it’s really exciting when you find the key that unlocks the solution to a problem.”

Growing up in Chile, Cristi enjoyed discussing science with his parents – his father is a veterinarian and his mother a nurse – and his brothers. Those discussions fueled Cristi’s interest in scientific disciplines. After graduating with a PhD in engineering systems, Cristi left Santiago last summer to take a position at EPFL, where he’s advancing his research on algorithmic game theory. “It’s a cross-disciplinary field that pulls together economics, computer science and management, using mathematical models as its foundations,” says Cristi, who began studying it during his master’s degree.

Overhauling the university admissions system

Cristi started out studying physics but found that mathematics gave him freer rein to explore his creativity. In 2011, while he was a bachelor’s student, a major political development in Chile gave him an opportunity to see how his field of study could be applied in practice. Many students at the University of Chile, including Cristi himself, protested against the inequality entrenched in the country’s education system. The government responded with a plan to reform several aspects of the system, including how seats in public and subsidized schools were allocated. Following this, the government asked one of Cristi’s professors to develop a new admissions process that would be rolled out across the country. Every public and subsidized school in Chile had its own admissions criteria, and the goal was to set up a centralized system that could handle all applications, making the process fairer and more efficient. “This project showed me I could have a direct impact by combining engineering and mathematics,” says Cristi.

It was his first tangible application of algorithmic game theory. “In the system we developed, various agents – in this case, schools and parents – interact via an algorithm. Parents read through the schools’ websites, and the algorithm suggests certain schools based on their admissions criteria,” says Cristi. “The catch was that our algorithm had to account for the fact that people make different choices based on their own interests and often change their minds. That complicated things considerably.” To overcome this problem, one of the things the engineers incorporated into their algorithm was incentive compatibility constraints. “That incentivized agents to give honest answers, resulting in the best possible outcomes for all stakeholders and helping to ensure that users’ personal interests were met,” says Cristi. It was this work on incentive compatibility that he found particularly interesting, as it was akin to finding that missing piece of the puzzle. Between 2016 and 2019, the system that Cristi and his colleagues developed was gradually implemented, and to this date it continues operating nationwide.

Explaining things in different ways

Cristi studied this topic further during his master’s and PhD, where he delved deep into the theory. He examined different market models and their mechanisms in order to better understand the underlying principles.

Today, algorithmic game theory is used in fields ranging from the design of online ad auctions to the planning of road systems to minimize traffic congestion. Cristi, who’s in the process of forming his research group at EPFL, currently teaches dynamic mathematical models of random phenomena to master’s students. “I really enjoy passing on my knowledge, and I try to explain things in various ways so that everyone can understand,” he says. “It’s an exercise that I personally find useful.”

When Cristi isn’t on campus, he can be found exploring Switzerland with his wife and meeting the locals. The couple has found fondue to be to their liking, and their next winter adventure will be sledding down the Alps.