Robert Duncan Luce, an influential mathematical psychologist at UC Irvine, died Saturday. In a career that spanned more than half a century, Luce applied the power of mathematics to describe human behavior.

"We’re talking about an intellectual giant," said UC Irvine economist Don Saari, a colleague of Luce.

Before Luce’s research, mathematics mostly described the physical world, calculating the speed of light or the freezing point of sugar water.

"But when we’re talking in terms of pain, or when we’re talking in terms of hunger, or we’re talking in terms of a lot of the issues that crop up in behavior ... These issues were not carefully defined until Luce and his co-authors tackled [them],” Saari said.

Luce’s research also led to a better understanding of the reasons consumers pick one brand over another and whether many options affect the choice. It does not, he wrote in 1959, when he presented "Luce’s Choice Axiom."

Before he joined the Irvine faculty in 1972, Luce had already taught at MIT, Columbia University and the Institute for Advanced Study. In 2003, Luce became the first social scientist to win the National Medal of Science.

"Duncan Luce was an internationally significant scholar for over half a century," said UC Irvine Chancellor Michael Drake. "The world has lost a great scholar, and we have lost a great friend. He will be missed."

The university said Robert Duncan Luce died after a short illness. He was 87 years old.