Grey relational analysis (wikipedia)
Grey relational analysis (GRA), also called Deng's Grey Incidence Analysis model, was developed by a Chinese Professor Julong Deng of Huazhong University of Science and Technology. It is one of the most widely used models of Grey system theory. GRA uses a specific concept of information. It defines situations with no information as black, and those with perfect information as white. However, neither of these idealized situations ever occurs in real world problems. In fact, situations between these extremes, which contain Dispersed knowledge (partial information), are described as being grey, hazy or fuzzy. A variant of GRA model, Taguchi-based GRA model, is very popular in engineering.
Introduction to Grey System Theory - by Deng Julong (PDF)
Grey System theory was initiated in 1982 [7]. As far as information is concerned, the systems which lack information, such as structure message, operation mechanism and behaviour document, are referred to as Grey Systems. For example, the human body, agriculture, economy, etc., are Grey Systems. Usually, on the grounds of existing grey relations, grey elements, grey numbers (denoted by 8 ) one can identify which Grey System is, where "grey" means poor, incomplete, uncertain, etc. The goal of Grey System and its applications is to bridge the gap existing between social science and natural science. Thus, one can say that the Grey System theory is inter- disciplinary, cutting across a variety of specialized fields, and it is evident that Grey System theory stands the test of time since 1982. As the case stands, the development of the Grey System-as well as theoretical topic-is coupled with clear applications of the theory in assorted fields.