## Character experience

Li Yapuov (александрмихайловичляпунов, 1857-1918) Russian mathematician, musicalist. On June 6, 1857, born in Yaroslavl; on November 3, 1918, died in Odessa. When I graduated from the middle school in 1876, I was admitted to the Gold Medal Department of St. Petersburg University. The knowledge of the University of St. Petersburg was deeply attracted to the knowledge of the famous mathematician Cut Bibbev. Under the influence of Pie Bikov, Zorota, he wrote a paper with an innovated paper in the fourth grade of the university, and got a gold medal. In 1880, college graduates were working in school, and the Ph.D. was also a professor in 1892. In 1893, he served as a professor of Harkov University. He was elected for the communication academician of the St. Petersburg Academy of Sciences in 1901. He was elected as Academician. In 1909, he was elected as a foreign academician of the Italian Guoqin Academy of Science, in 1916, is elected as a foreign academician of the Paris Academy of Sciences.

## Academic achievement

** Cut Bikov founded the outstanding representative of Petersburg learning **

Li Yapopnov is Cantophili created The outstanding representative of the St. Petersburg learned, his construction tree involves a number of fields, especially in probability, differential equations, and mathematical physics.

** created characteristic function method **

In the probability theory, he created a feature function method, achieving a breakthrough in the research method, this method is characterized by retaining all the information distribution of random variables, providing the convergence of characteristic functions. A correspondence between the convergence properties of the nature and distribution function, gives a simple and strict prove that the Pimple, Markov on the central limit is simpler, and he also uses this reason for the first scientific explanation. Why did many random variables encountered in the actual approach to normal distribution. His construction tree for probability theory mainly published in its 1900 "probabilistic theory" and 1901 "probabilistic disclosure of new form" paper His approach has been widely used in modern probability. This work is later by A. A. Markov inherited.

** Original Differential Equation Sports Stability Theory The founder **

Li Yapopnov is one of the founders of exercise stability theory in mechanics. Sports Stability Problem has studied many scholars in the second half of the 19th century, and has some results, such as J · C, famous physicists. Maxwell (1868) analyzes the paper "discipline" and E of steam machine governor and clock mechanism stability. J. Monographical "Stability of Motion Status" (1877), H. E. Confucian "Persistence" (1882), etc. Li Yapopnov and France H. Pangolan studied general problems in motion stability theory from different perspectives. Li Yapopnov adopted a pure mathematical analysis method, and Poacle focused on geometric and topological methods. Li Yapov was completed in 1884, "On a stability of a rotating liquid balanced surface shape", in 1888, he published "the stability of mechanics system with limited freedom", especially his 1892 Ph.D. The "General Problem of Sports Stability" is a classic masterpiece. The stability of the known motion status is given a strict mathematical definition in the text, and the first set is suitable for motion status as a known situation. The second set is completely qualitative, as long as you know the differential differentiation equation. The latter set method is widely used in the 20th century to analyze the mechanical system and the automatic control system, and the ** of the nonlinear neutral differential equation is proposed in it, which is also known as the direct method. It linked to the stability of the solution with a function of a special nature (now known as Li Yapopov function), which has certain nature of the derivative along the track about time. It is because of this The obvious geometric intuitive and concise analytical skills of the method are prone to the actual and theoretical workers, thereby extensively apply and develop in many fields of science and technology, and laid the basis of the stability theory of normal differential equations. It is also an important means of the genialization theory of normal differential equations. **

** The balanced shape of the rotating fluid and its stability **

Li Yapopov also studied the balanced shape of the rotating fluid and its stability. This problem is related to the origin of the celestial strength. Pangola has proposed a balanced shape that is likely to be born from an ellipsoid (called bifurcation). Li Yapopnov pointed out that this pear shape was unstable, and his research was later j. Jones confirmed in 1917.

** Developed a new way to the development of mathematical physics methods **

Li Yapopov's research on the theory of position is open, the development of mathematical physics methods has opened up new The way. The paper published in 1898 "Some research on Diyaki problem" is also an important paper. The text of the first time, a few basic properties of the single layer, the double-level position, pointed out Several charges of this issue in this issue is here. His research results laid a basis for the classic method of boundary value issues.

** Mathematical concept named by last name **

in mathematics with his surname name: Li Yapopnov first method, Li Yapopnov second method , Li Yapopnov, Li Yapov, Li Yapopnov curve, Li Yapopnov curve, Li Yapuov, Li Yapuov, Li Yapopnov random function, Li Yapuov random calculator, Li Yapu Novi Index, Li Yapopnovvi, Li Yapopnov System, Li Yapopnov, Li Yapopov Stability, etc., which has a variety of conditions in his surname named.