The Sample Number Selection Rules Study on Grey Forecast Model

To establish GM(1,1) model or the discrete GM(1,1) model, how to select the proper sample should be decided first, but no satisfied rules has been put forward about the selection of the sample number. The paper makes a comparable complete study on the selection rule about sample data. It proves that the growth rates of the fitted value of the GM(1,1) model and the discrete GM(1,1) model are both fixed value. If the growth rates of the primary sequence are equal, the fitted value deriving from the discrete GM(1,1) model the same as the primary sequence. The closer the growth rates of the sample are, the smaller the average absolute error of sample data is. If the average absolute error of the growth rates is smaller enough, the sample data can be regarded as the same circle data. According to the above study, the paper puts forward the selection rules of the sample data.