By grey system theory I mean the one defined by Deng Julong in 1982. '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.', Deong Julong.
A lot of research in grey system theory has been done since 1982. There are books and articles, but performing all the calculations manually is not effective, especially when some changes have to be introduced repeatedly.