1. Deng JL (2002) The foundation of grey theory. Huazhong University of Science and Technology Press, Wuhan
2. Deng JL (2002) Grey forecasting and grey decision-making. Huazhong University of Science and Technology Press, Wuhan
3. Mao SH, Xiao XP (2007) On the properties of a kind of smoothing operator. J Grey Syst 19:57–66
4. Xiao XP (2005) The foundation and application of grey technology. Science Press, Beijing
5. Liu SF, Deng JL (1999) The range suitable for GM(1,1). J Grey Syst 11:131–138