Speech at the Opening Ceremony of the 40^th Anniversary Commemorative Exhibition of the Founding of Grey System Theory

29^th November, 2022

First of all, I congratulate on the grand opening of the 40th anniversary of the birth of the grey system theory, and congratulate on the important influence of the grey system theory created by Chinese scientists in the world.

In the researches of natural sc  ience, social science technology and engineering, due to the limitation of people's cognitive ability and the internal and external d isturbance of the research object, the available information is always uncertain. The second half of the 20th century, with the deepening of people's understanding of system uncertainty, witnessed various theories and methods proposed to describe uncertain systems from different perspectives, including fuzzy mathematics, rough set theory and grey system theory. Among them, fuzzy mathematics deals with cognitive uncertainty and focuses on the objects with "clear connotation and unclear extension"; Rough set theory analyzes data based on equivalence relations, using upper and lower approximation sets to describe the boundary region of uncertain concept extension; The grey system theory focuses on the objects with "clear extension and unclear connotation" and the poor information uncertainty system with unknown distribution.

The grey system theory mainly extracts valuable information through mining of “a part" of the known information, and realizes the correct description of the system operation behavior and evolution laws. As such, people can use mathematical models to realize the analysis, evaluation, prediction, decision-making and optimization control of uncertain systems with "poor information". The uncertainty systems with "poor information", which widely exist in the real world, have provided rich research resources and broad development space for the grey system theory.

Professor Sifeng Liu has devoted himself to the research field since the birth of the grey system theory. Over the past 40 years, he has led a group of young scholars to make a systematic and innovative study on the theories, methods and models of grey system and spread the kindling of grey system research to the whole world with the firm belief of "a group of people, a whole lifetime and a unique persuit".

I got to know Prof. Liu at the turn of this century and worked together with him at Nanjing University of Aeronautics and Astronautics for many years. I was happy to see that Prof. Liu, as the Chair Professor of Management Science and Engineering, founded the corresponding doctoral program, which was successfully approved by the State Council, at NUAA and promoted the College of Economics and Management of NUAA to a more advanced level. I have kept paying attention to his academic research since I moved to Beijing Institute of Technology. It is gratifying to see that he has made a series of important theoretical and applied research achievements by persisting in studying real problems, pursuing real contributions and creating real value for a long time.

Recently, Professor Sifeng Liu, through an in-depth analysis of the reliability growth data of major aerospace equipment, found that it has the coexistence characteristics of random, fuzzy, gray and rough data, and thus proposed new concepts such as general uncertainty data (GUD) and general uncertainty variable (GUV), which opened a new door to reliability growth research. In his late seventies, he still maintains the evergreen academic tree, which is encouraging young students to make unremitting efforts to climb the peak. I believe that NUAA will have a better tomorrow, and the grey system theory will have a better tomorrow!

Finally, I wish that the Chinese scientists will continue to make new discoveries, put forward new concepts, create new theories and realize the dream of becoming a powerful nation in science and technology as early as possible!

                                                                                                             Haiyan Hu

                                   Academician of the China Academy of Sciences and 

                                   former President of Beijing Institute of Technology