Qin Yuanxun returned to Guiyang on 1948 and married Ms. Feng Min, who graduated from the Foreign Languages Department of Guizhou University. From then on, the two loved each other and lived together. Feng is a good helper of Qin, and Qin's achievements cannot be separated from her unknown help. 1On October 20th, Feng Min died of a sudden cerebral hemorrhage. Shortly after marriage, Qin went to Hong Kong to participate in the liberation struggle. Co-founded the Hong Kong and Kowloon Scientists Association with Cao Richang and served as the Vice Minister of Commerce (the minister is

Zeng Zhaolun). The main tasks are: to unite scientists who have been to Hong Kong and worked in Hong Kong and Kowloon; Comrades in charge of logistics and their families were transported to the liberated areas. In Hongkong, he wrote a General Theory of Geometry as a gift to the founding of New China (the book was reprinted twice). 1949, Xinhua News Agency of Hong Kong invited Qin, as one of the three representatives of Hong Kong (the other two were Cao Richang and Yan Xichun), to go to the liberated areas to participate in the preparations for the first conference of the Association for Science and Technology. At that time, I was faced with two choices: to go to the Liberated Area or to the United States to do business for the China Producer Party. Qin chose the former, took a boat from Hong Kong to Dalian to enter the Northeast Liberated Area, and arrived in Beiping in July of the same year. In addition to participating in the preparation and attending the first National Association for Science and Technology Conference, he was also hired as an associate professor in the Department of Mathematics of Beijing Normal University. When celebrities at home and abroad gathered in Beijing, Chen Yi mobilized people from Beijing to work in the frontier on behalf of the CPC Central Committee. Once again, Qin Yuanxun was faced with two choices: whether to stay in Beijing as a professor or to work in a remote area. Qin chose the latter. He took off his overseas fashion, put on the gray cotton-padded jacket of the Second Field with his wife Feng Min, put on his simple luggage, and went to Chongqing with Chu Tunan, living with only two yuan of pocket money a month. He recalled: "Why bother about personal life when the construction of new China is like mushrooms after rain?" 1950 to 1953 served as deputy director of the research office of the Culture and Education Department of the Southwest Military and Political Commission (Minister Chu Tunan) and director of the Science Popularization Department, and participated in taking over and rectifying the cultural and educational undertakings of the Southwest Administrative Region; Formulate the adjustment plan of colleges and departments in colleges and universities; Establish popular science institutions and associations in southwest China; The establishment of southwest cultural center system is very busy. /kloc-in the autumn of 0/953, the southwest region was revoked and transferred back to Beijing as the director of the Planning Bureau of the Chinese Academy of Sciences. 1954 ——1959 for the need of developing new disciplines in China, I worked as an associate researcher and deputy director (director is Wu Xinmou) in the Institute of Mathematics of China Academy of Sciences, engaged in the study of ordinary differential equations. At the same time, he is also the chairman of the Beijing Mathematical Society (1955- 1964), the Standing Committee of the National Association for Science Popularization (1950- 1958) and the Standing Committee of all-china youth federation (1955- 1959).

Qin returned to China to take part in the revolution after receiving his doctorate in the United States. 1950 joined the new-democratic youth league, and in the same year joined the Jiu San Society as a member of the National Science and Technology Committee of the Jiu San Society. When the new China was founded, the same program emphasized "popularization first". Qin Yuanxun devoted himself to the popular science cause in the newly born new China with a fiery heart, taking the needs of the country as his own responsibility. 1959, joined the China * * * production party.

1953, the delegation of China Academy of Sciences suggested that two "tentacles"-differentiation-must be developed when combining mathematical theory with practice.

Equation (deterministic law) and probability theory (stochastic law). Qin was invited by the director of China Institute of Mathematics to undertake the task of sorting out and developing ordinary differential equations in China. Together with other scholars, he established China's qualitative theory of ordinary differential equations and theoretical team of motion stability through various forms of training. In the past 30 years, we have introduced and developed two branches of real certainty theory and motion stability theory, and created two new branches of complex certainty theory and approximate analytical solution with China characteristics. In recognition of his achievements, at the 1978 scientific conference, his 100-word Research on Systems of Ordinary Differential Equations was awarded a major achievement award. In 1950s, Qin Yuanxun was one of the youngest and most promising experts at that time. He inherited and developed the research work initiated by four papers published by the famous French mathematician Poincare in 188 1, 1882, 1885, 1886, that is, directly drawing the integral curve of the definition of differential equation and writing the definition of differential equation. Research on limit cycles, * * * published 16 (volume) (1954- 1960). Among them, the regional analysis theory can roughly determine the position of the limit cycle; In 1955, it is given for the first time that (E2) has a specific type of limit cycle, which is the only known quadratic system with expression. He and his graduate student Pu Fuquan (later Professor Tsinghua University) provided a method to construct a concrete example of a quadratic system with three limit cycles near the singularity. Instructed graduate student Dong Jinzhu (who later became a professor at HKUST Graduate School) to solve the relative position distribution of limit cycles of quadratic systems. These important achievements have been recognized and cited by scholars at home and abroad.

Qin Yuanxun led Wang Lian, Wang Muqiu (now a researcher at the Institute of Mathematics of China Academy of Sciences), Liu Yongqing (now a professor at South China University of Technology) and Jolin Tsai (now a professor at Zhejiang University) to study the stability of time-delay systems and the decomposition of large-scale systems into subsystems. He was the pioneer of the theory of large-scale system stability decomposition. The boundary of delay control parameters of combustion instability proposed by Qian Xuesen is solved. This achievement was translated into Russian and published in the Soviet Union as one of four papers submitted by China to the first international automation conference held in Moscow in 1960. These achievements are summarized in two books published in China: Lecture Notes on General Problems of Motion Stability (1958) and Motion Stability of Dynamical Systems with Time Delay (1963).

Due to the need of work, Qin Yuanxun was transferred from China Academy of Sciences on 1960, and his pure theoretical research on differential equations was suspended. (3) 1979 started the research on computer formula derivation of ordinary differential equations, which belongs to the category of "artificial intelligence". Qin cooperated with Liu Zunquan and Qin Chaobin, and realized the complex central focus discrimination formula in quadratic differential system through symbolic operation of computer. It is found that there is a key symbol error in the famous result of Bawujin, an academician of the Soviet Academy of Sciences. After correcting the error, the criteria of quadratic differential equations with all parameters are obtained. The research achievements in this field, with the title of "New Application of Computer", won the second prize of major achievements of China Academy of Sciences. At the same time, Qin initiated and organized the Chinese Society of Artificial Intelligence in 198 1 and became the first director (1981987), which promoted the development of this new field in China. Study on variable coefficient system, nonlinear system and Riccati equation (4) Study on variable coefficient system, nonlinear system and Riccati equation. Published the book "Theory and Application of Motion Stability" (198 1 year).

Qin's consistent academic guiding ideology is to overcome difficulties, establish new branches, find out the basic laws of differential equations and solve difficult problems by the way. He believes that there is no depth without attacking difficult problems; Only by solving difficult problems can we not draw a systematic new theory, nor can it be regarded as a great contribution to mathematics. From 65438 to 0980, in order to meet the needs of economic development, mathematical research on economic work was carried out. For example, the establishment of agricultural database, comprehensive transportation planning, the study of the optimal product-consumption ratio and so on.

In a word, Qin Yuanxun is engaged in both pure theoretical mathematics research and practical research to solve practical tasks; It has not only introduced international advanced disciplines, but also established a new branch discipline with China characteristics, which has achieved important results.

Qin is enthusiastic about cultivating scientific and technological talents and caring about the growth of young people. He has a set of training methods that can quickly bring a large number of cadres into the front line of scientific research. From 1954 to 1960, a group of talents in differential equations have been trained. From 1960 to 1972, the first nuclear power computing team was brought out; 1973- 1976, some students in the middle school attached to Peking University received training in their spare time, entered the university with excellent results, and some went abroad for further study; From 1977 to 1984, the computational physics team in China was trained. Since 1978 resumed postgraduate enrollment in China, a * * * has trained 23 postgraduate students, 6 doctoral students and 9 senior teachers. These students of Qin Yuanxun have achieved excellent results in their own research. Most of them are employed as professors and associate professors, and many of them hold leadership positions in important positions.

Qin attaches great importance to the popularization of science. In the early days of the founding of the People's Republic of China, he personally popularized and wrote many popular science books. For example, the general theory of geometry, space and time, from arithmetic to ordinary differential equations, infinite mathematics, mathematics self-study series in secondary schools, etc. He often makes reports on popular science work in simple terms, which is very popular with the audience. His point of view is: "readers can't understand, the problem lies in the author;" If the author really understands, he should let the readers understand in his own language, which shows that the author really understands. "Qin actively carried out international scientific exchanges and cooperation activities. He invites and receives many foreign tourists every year. Since 1980, he has also frequently visited and inspected abroad. For example, from September to October of 1980, he visited more than 20 famous American universities, companies and advanced research institutes as a member of the China mathematician delegation. Participated in the first and fourth international "Double Micro" conferences held in Beijing, China in August 1980 and September 1983; 1May, 984, visited eight famous universities in Britain. In July, he attended the 8th International Conference on Differential Equations held in Dandy and visited the Paris Institute for Advanced Studies. 1985 visited the traffic information system in Britain for two weeks and gave lectures in West Germany. Also signed a three-year (1986- 1988) talent exchange agreement with Birmingham University; Academic visit to Hungary and Romania from May to June,1986; 1August 1987 to1August 1990 as a visiting professor in the Department of Mathematics, University of Florida.