This invention generally relates to methods, apparatus and computer program code processing digital data using non-negative matrix factorisation. The optical head includes a unit for correcting the spot shape between the objective lens and a photodetector device. Namely, when the battery temperature is low and the catalyst temperature is also low, the catalyst warm-up is given a higher priority than the low SOC control and prevents the exhaust emission from becoming worse. The storage device receives information stored in the non-volatile memory cell.