CONSTANTIN V ˆ ARSAN ON HIS 70th BIRTHDAY
Constantin Vˆarsan, an outstanding Romanian researcher in differential equations and stochastics, was born on May 18, 1939 in the town of Constant¸a, Romania. After basic and middle schooling in his native town, he studied at the Faculty of Mathematics and Physics with major in Mathematics, gradua- ting in 1962. In 1966 he started the doctoral studies at IMAR (Institute of Mathematics of the Romanian Academy) in the field of Variational Calculus, under the advisorship of Professor Miron Nicolescu (1903-1975), member of the Romanian Academy. Working under the direct advisorship of Professor Aristide Halanay (1924-1997) whose scientific seminar On Qualitative Theory of Differential Equations Vˆarsan joined in 1962 and is now leading (together with T. Morozan), he obtained his Ph.D. degree in 1969 with the thesis entitled
“Abstract multiplier rule applied to control systems”.
After seven years (1962-1969) spent as an instructor (teaching assis- tant) at the School he graduated, in the Department of Mathematical Ana- lysis, Vˆarsan joined the staff of the Institute of Mathematics of the Roma- nian Academy where he remained up to now: researcher, senior researcher and head of division, he served between 1975 (when the Institute of Mathe- matics practically ceased its existence) and 1990 at the Mathematics Section of INCREST (National Institute of Scientific Creation) as senior researcher of IIId then of IInd degree. Since 1990 he returned at the Institute of Mathe- matics and became senior researcher of Ist degree (highest research degree – equivalent to Professor in the University system). Also since 1990 he was head of the Division of Differential Equations, Optimal Control and Equations of the Mathematical Physics. In 1993 he obtained Ph.D. advisorship in the field of Differential and Partial Differential Equations. Up to now 6 doctoral stu- dents in Mathematics obtained the Ph.D. degree under Vˆarsan’s advisorship.
The research interests of Vˆarsan as reflected by his scientific publications are oriented towards some traditional directions of the Mathematics world research. The first group of papers is dedicated to nonlinear control problems with infinite dimensional restrictions. The second one, which may be viewed as some kind of extension of the first, deals with the theory of the nonlinear
MATH. REPORTS11(61),4 (2009), 275–277
276 Vladimir R˘asvan 2
controllability. The third group of papers, which starts after 1993, is concerned with stochastic differential and partial differential equations, based on gradient systems associated with finite/infinite dimensional Lie algebras.
The remarkable results of Vˆarsan were published in some 60 scientific papers and 4 monographs (books) – a rather high scientific production if one thinks to his mathematical rigor and his self-requirement level. The best ap- preciation of the scientific achievements of Vˆarsan is undoubtfully the cita- tion and continuation of his results. Starting with his Ph.D. thesis, whose main results were published in SIAM Journal on Control and Optimization, he was cited by such personalities as L.W. Neustadt (in 1974, SIAM Jour- nal on Control) and A.A. Dubovitskii (in his Doctoral thesis, 1975), also by A.B. Schwarzkopf (in 1975, SIAM Journal on Control). It is quite well known the high level of the surveys published by Russian Mathematical Sur- veys (Uspekhi Matematicheskikh Nauk). One of these surveys, authored by such recognized mathematicians in the field of Optimal Control, as E.S. Levi- tin, A.A. Milyutin and N.P. Osmolovski, is citing 5 of the papers of Vˆarsan while other two have been discussed within the 6th section of the survey.
Regarding the papers dedicated to nonlinear controllability we recall that an early IMAR preprint (lately published in Rev. Roumaine Pures Appl. 10 (1984)) was largely commented and discussed by H.W. Knobloch in the Con- trol Theory section of the World Mathematical Congress in Warsaw (1984).
The four books of Vˆarsan also got a worldwide recognition. The first one, “Abstract problems of restricted optimum applied to control”, published in 1974 and awarded the “Simion Stoilow” award of the Romanian Academy, is cited and commented in such a Survey Journal as Contemporary Mathematics (Russian, 1976). We have already mentioned a third research direction of Vˆarsan: the obtained results on stochastic differential equations are gathered in his monograph “Applications of Lie algebras to Hyperbolic and Stochastic Differential Equations” (Kluwer Academic Publishers, 1999). Not only that it received a remarkable review, but various reviewers of MathSciNet have cited this monograph in connection with other reviewed material. Also its results and their implications in such strikingly actual fields as Finance mathematics constituted the scientific basis for the 6 (up to now) Ph.D. theses elaborated under the advisorship of Vˆarsan.
As a University professor, he elaborated and taught courses both for his School (Faculty) of Mathematics of Bucharest University and for the “Ovidius”
University of his native town, Constant¸a. He delivered a similar activity also abroad: invited speaker at numerous scientific international conferences and seminars, he delivered talks and courses at the Banach Center in Warsaw and at the International Center of Theoretical Physics in Trieste. During the academic year 1978/1979 he was accepted, as a consequence of a competition,
3 Constantin Vˆarsan on his 70th birthday 277
as visiting professor in Hiroshima University, by the Japan Society for the Promotion of Science.
Now at 70 but still active and creative, the distinguished mathemati- cian Constantin Vˆarsan is greeted by his colleagues and friends, by the entire Mathematics Community of Romania.
Vladimir R˘asvan
