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[[Image:POPOV.JPG|right|thumb|150px|Vasile Mihai Popov]]
'''Vasile Mihai Popov''' (born 1928) is a leading [[system theory|systems theorist]] and [[control engineering]] specialist. He is well known for having developed a method to analyze [[stability theory|stability]] of nonlinear [[dynamical systems theory|dynamical systems]], now known as [[Non-linear control#Popov criterion|Popov criterion]].

== Biography ==
He was born in [[Galaţi]], [[Romania]] on July 7, 1928. He received the engineering degree in electronics from the [[Bucharest]] [[Polytechnic University of Bucharest|Polytechnic Institute]] in 1950. 

He worked for a few years as Assistant Professor at the [[Polytechnic University of Bucharest|Bucharest Polytechnic Institute]] in the Faculty of Electronics. His main research interests during this period were in frequency modulation and parametric oscillations. In the mid 1950s, he joined the Institute for Energy of Romanian Academy of Science in Bucharest. In the 1960s, Popov headed the Control group at the Institute of Energy of the [[Romanian Academy]].

In 1968 Popov left Romania. He was a visiting professor at the Electrical Engineering departments of [[University of California, Berkeley]], and [[Stanford University]], and then Professor in the
department of electrical engineering at the  [[University of Maryland College Park]]. In 1975 he joined the mathematics department of [[University of Florida]] Gainesville. 

He retired in 1993 and currently resides in [[Gainesville, Florida]], USA.

== Work ==
=== Qualitative theory of differential equations ===
Motivated by stability issues in nuclear reactors and by his participation in a seminar series on qualitative theory of [[differential equations]] run by [[A. Halanay]], Popov started working in stability of nonlinear [[feedback]] systems, in particular on the [[Lur'e-Postnikov problem]]. 

In 1958/59 he obtained, through a very original approach, the first frequency stability criterion for a class of nonlinear feedback control systems. He continued this work and obtained the equivalence between the [[state space]] ([[Lyapunov function]] based) approach and the frequency domain approach for stability and obtained a very perceptive characterization of [[Passivity (engineering)|passive]] systems, nowadays known as the celebrated [[Kalman–Yakubovich–Popov lemma]].

=== Hyperstability ===
In the early 1960s, Popov also conceived the notion of [[hyperstability]], a concept that he viewed as generalization of [[absolute stability]]. This introduced a new and a very fruitful point of view for the analysis and synthesis of nonlinear feedback systems. 

This research work was published in the first half of the sixties and led to the book ''Hyperstability of Dynamic Systems'', first published in Romania in 1966, and subsequently translated in French and English ([[Springer Science+Business Media|Springer-Verlag]], 1973). Popov was also the first to discover the geometric invariants of linear systems with respect to certain "transformation groups" and he introduced a "canonical" form for uniquely describing the multivariable systems.

== References ==
*{{cite journal|first=B.D.O.|last= Anderson|coauthors=P. Kokotovic, I.D. Landau and J.C Willems|title=Dissipativity of dynamical systems: applications in control -- dedicated to Vasile Mihai Popov|issue=Special issue|journal=European Journal of Control|volume=8|year=2002}}.

{{Authority control|VIAF=17754161}}
{{Persondata <!-- Metadata: see [[Wikipedia:Persondata]]. -->
| NAME              = Popov, Vasile M.
| ALTERNATIVE NAMES =
| SHORT DESCRIPTION =
| DATE OF BIRTH     = 1928
| PLACE OF BIRTH    =
| DATE OF DEATH     =
| PLACE OF DEATH    =
}}
{{DEFAULTSORT:Popov, Vasile M.}}
[[Category:1928 births]]
[[Category:American mathematicians]]
[[Category:Control theorists]]
[[Category:Living people]]
[[Category:People from Galaţi]]
[[Category:Romanian mathematicians]]
[[Category:American people of Romanian descent]]
[[Category:Politehnica University of Bucharest alumni]]
[[Category:Politehnica University of Bucharest faculty]]⏎
⏎
[[ht:Vasile Popov]]
[[ro:Vasile-Mihai Popov]]