View source for Raimo Juhani Ylinen

{{Infobox scientist
| name = Raimo Juhani Ylinen
| alt = Raimo Juhani Ylinen
| residence = Espoo, Uusimaa, Finland
| nationality = Finnish
| fields = [[Systems theory]], [[control engineering]], [[mathematics]]
| workplaces = [[University of Oulu]]; [[Helsinki University of Technology]] ([[Aalto University]])
| known_for = [[Polynomial systems theory]], algebraic theory of multivariable linear systems
}}

'''Raimo Juhani Ylinen''' is a Finnish [[systems theory|systems]] and [[control engineering|control]] theorist and mathematician, professor emeritus at the [[University of Oulu]] and docent in systems theory at the [[Helsinki University of Technology]] (now part of [[Aalto University]]). He is known for his work on the algebraic, or [[polynomial systems theory|polynomial systems]], approach to multivariable linear systems.

==Biography==
Ylinen carried out much of his early career at the Systems Theory Laboratory of the Helsinki University of Technology, where from the late 1960s he took part in the development of an algebraic theory of dynamical systems. Working with [[Hans Blomberg]], he co-authored the monograph ''Algebraic Theory for Multivariable Linear Systems'' (Academic Press, 1983), which became a standard reference in the field.

He later served as professor of automation and control engineering (systems engineering) at the University of Oulu, where he was appointed in 1997 and held a permanent chair from 2002 until his retirement in 2003. He subsequently continued to publish as professor emeritus and remained a docent in systems theory. He resides in Espoo, Finland.

==Work==
Ylinen's research centers on [[polynomial systems theory]], an algebraic framework in which the input-output behavior of linear systems is described by [[polynomial matrix|polynomial matrices]] and the associated algebraic structures such as [[principal ideal domain]]s. This approach provides a unified treatment of properties such as [[controllability]], [[observability]] and [[stability theory|stability]], and supports observer and controller design carried out by purely algebraic methods.

He extended the framework beyond constant-coefficient systems by employing skew polynomial (Ore) algebra to represent linear time-varying input-output differential systems, allowing many methods of ordinary polynomial systems theory to be applied to time-varying models. Through global linearization of nonlinear input-output descriptions, he further applied these skew-polynomial techniques to the analysis and feedback design of nonlinear systems, and to the study of multidimensional and distributed-parameter systems.

==External links==
* [https://epubs.siam.org/doi/abs/10.1137/1027050 ''Algebraic Theory for Multivariable Linear Systems'' (H. Blomberg and R. Ylinen), review in SIAM Review]
* [https://eudml.org/doc/207620 "Polynomial systems theory applied to the analysis and design of multidimensional systems" (2003)]

[[Category:Scientist|Ylinen Raimo]]