1. A method comprising: providing, by an apparatus, a data structure comprising context vectors and operational state vectors of a plurality of operational units in a system, the data structure having an association between said context vectors and said operational state vectors, and the operational units including hardware, software applications, or a combination thereof; receiving, by the apparatus, a context vector of the system; using, by the apparatus, said context vector and a distance measure to select a plurality of operational state vectors, the plurality of operational state vectors being indicative of operational states and respective power consumption states of the operational units, and the respective power consumption states including one or more power-performance ratios and one or more transition costs; and modifying, by the apparatus, the selected operational state vectors using a teaching operational state vector associated with said context vector by increasing a value of an element corresponding to the active operational unit in the teaching operational state vector according to said distance measure.