In January 2020, there was the Centennial of outstanding mathematician, expert in Approximation Theory, Professor M. P. Korneichuk (1920–2003). On this occasion Institute of Mathematics of National Academy of Sciences of Ukraine, Oles Honchar Dnipro National University, Taras Shevchenko Kyiv National University, Giessen University (Germany) are organizing the International Scientific Conference that will be held in Dnipro, Ukraine, on September 16–19, 2020.

# «APPROXIMATION THEORY

# AND ITS APPLICATIONS»

Mykola Pavlovych Korneichuk was born on the 22nd of January 1920 in the village Bobryk of Petrykiv district of Gomel region, Belarus, in a peasant family. In 1938 he graduated from the industrial-pedagogical college, worked as a teacher of Mathematics. From 1940 to 1949 he served in the ranks of the Soviet Army, fought on the fronts of the Great Patriotic War, was twice wounded, was awarded the Order of the Patriotic War of the 1st degree and the Red Star, the medal “For the victory over Germany”.

Immediately after his demobilization, Mykola Pavlovych worked as a teacher of Mathematics in Pavlograd, Dnipropetrovsk region, and at the same time studied by correspondence at the Physics and Mathematics Faculty of Dnipropetrovsk State University (DSU), graduating with honors in 1955. In 1958 he finished postgraduate studies at the Department of Mathematical Analysis of DSU. Having started scientific research late, M. P. Korneichuk quickly declared himself in the Mathematical world. In 1959 he defended his PhD thesis “Some questions on the approximation of periodic functions by trigonometric polynomials”. In 1961 he solved famous Favar’s problem, and two years later successfully defended his doctoral thesis “On the best uniform approximation of continuous functions” at V. A. Steklov Mathematical Institute of USSR Academy of Sciences. In 1963 he became the head of Department of Functions Theory of DSU. In 1965 he received the academic title of Professor. M. P. Korneichuk had been heading the Department of Approximation Theory of Institute of Mathematics of Academy of Sciences of Ukraine since 1974.

In 1970 M. P. Korneichuk brightly competed the cycle of works on exact estimates of the best approximations by trigonometric polynomials of classes of differentiable functions. Moreover, he developed a method of sigma-rearrangements that became an effective tool for solving extremal problems of non-linear analysis. In 1980s Mykola Pavlovych worked on solving extremal problems, spline approximation, optimization of approximation methods. His significant results facilitated development of Approximation Theory inside Ukraine and abroad. The results of Mykola Pavlovych own research, as well as the results of his students’ researches, are summarized in eight monographs, both personal and co-authored, and in many papers on the problems in Approximation Theory. Scientific creativity and exceptional combination of high human qualities, pedagogical talent and outstanding organizational abilities allowed him to create a team actively working in the field of Approximation Theory, whose members defended more than 30 PhD and 8 doctoral theses.

For many years M. P Korneichuk headed Kyiv Mathematical Society, was the Deputy Academician-Secretary of the Department of Mathematics of NAS of Ukraine. For decades he was the head of the scientific seminar at the Department of Approximation Theory in Institute of Mathematics of NAS of Ukraine. It is impossible to overestimate M. P. Korneichuk’s contribution in training of scientific personnel of the highest qualification in the positions of the chairman of the specialized academic council for the defense of doctoral theses at Institute of Mathematics of NAS of Ukraine, as well as the chairman of the expert council of High Accreditation Committee of Ukraine in Mathematics. Mykola Pavlovych devoted a lot of energy and efforts to scientific editorial activities. He was the deputy editor-in-chief of the Ukrainian Mathematical Journal, a member of the editorial board of East Journal on Approximations, a member of the editorial council of Mathematical section of Proceedings of Institute of Mathematics of NAS of Ukraine, and the editor-in-chief of many volumes of journals in Approximation Theory published by Dnipropetrovsk University and Institute of Mathematics.

Mykola Pavlovych Korneichuk’s scientific and pedagogical achievements were highly regarded by the state. In 1967 he was awarded the Order of Lenin; and in 1980 – the Order of the Red Banner of Labor. In 1973 M. P. Korneichuk became a laureate of the USSR State Prize, and in 1994 – the State Prize of Ukraine in the field of science and technology. In 1998 Mykola Korneichuk was elected a full member of National Academy of Sciences of Ukraine. In 2000 M. P. Korneichuk (together with S. M. Nikolskii and O. I. Stepanets) was awarded the M. V. Ostrogradsky Prize of NAS of Ukraine for the series of works on Approximation Theory of functions. In the same year, by the decree of the President of Ukraine, he was awarded the honorary title “Honored Worker of Science and Technology of Ukraine”.

Thanks to his sincerity and humanity, his vivid mathematical talent, his tremendous perseverance and hard work, Mykola Pavlovych Korneichuk gained authority and respect of Mathematical community. His name is inscribed in gold in the world treasury of Approximation Theory of functions .