**5. Preparing the input data**

First step in the process of electricity load forecasting is to provide last information of the system load being studied. After preparing the input data matrix, it is turn of classification. The reason of this classification is the existence of completely determined models in different days that were referred to in many references. Among different days of weeks, Saturday to Thursday which are working days in Iran, have the same load model. Fridays have also their own particular model and have a low level of load. Special days have a completely different model, too. So it seems necessary at the first look that each of these classes should be analyzed separately. We consider 2 groups of features that refer to previous days; 2, 7, and 14 day ago, and 2, 3, 4 day ago.
