The supercomputer is a predictive model that uses a combination of Elo ratings and performance data to simulate the season thousands of times and predict the outcome of the league. After each matchday the simulator is updated with the actual results and the remaining fixtures are simulated to forecast the remainder of the season.
To calculate the match probabilities each game is simulated thousands of times with every result measured. From this we can deduce the probability of different outcomes and calculate a predicted xG for each team. The supercomputer also factors in home advantage for improved accuracy.