  The importance of low power consumption is widely acknowledged due to the
increasing use of portable devices, which require minimizing the consumption of
energy. The energy in a computational system depends heavily on the software
being executed, since it determines the activity in the underlying circuitry.
In this paper we introduce the notion of energy complexity of an algorithm for
estimating the required energy consumption. As test vehicle we employ matrix
multiplication algorithms and from the results it can be observed that energy
complexity in combination with computational complexity, provides an accurate
estimation for the energy consumed in the system.
