Judges in the Philadelphia court system are now taking advantage of powerful new computer models to help determine how much jail time an offender should get. Computers have been forecasting weather and economic trends for years, but applying algorithms to human behavior is relatively new. University of Pennsylvania professor Richard Berk, a pioneer in the field, his forecasts, which use an algorithm to predict whether someone will offend again, have been used by city probation and parole officers for about three years, to decide how much supervision a defendant needs.