Joseph Pierre LaSalle (born 28 May 1916 in State College, Pennsylvania; died 7 July 1983 in Little Compton, Rhode Island) was an American mathematician specialising in

dynamical systems In mathematics, a dynamical system is a system in which a function describes the time dependence of a point in an ambient space. Examples include the mathematical models that describe the swinging of a clock pendulum, the flow of water in a p ...

and responsible for important contributions to

stability theory In mathematics, stability theory addresses the stability of solutions of differential equations and of trajectories of dynamical systems under small perturbations of initial conditions. The heat equation, for example, is a stable partial diffe ...

, such as

LaSalle's invariance principle LaSalle's invariance principle (also known as the invariance principle, Barbashin-Krasovskii-LaSalle principle, or Krasovskii-LaSalle principle) is a criterion for the asymptotic stability of an autonomous (possibly nonlinear) dynamical system. Gl ...

which bears his name.

Biography

Joseph LaSalle defended his Ph.D. thesis on ″''Pseudo-Normed Linear Sets over Valued Rings''″ at the California Institute of Technology in 1941.J. P. LaSalle on the Mathematics Genealogy Project
/ref> In 1946 he joined the Mathematics Department at the University of Notre Dame as an assistant professor and remained there until 1958, becoming a full professor in 1956.SIAM J. Control Optim., 21(6), vii–ix. In Memoriam
/ref> During a visit to Princeton in 1947–1948, LaSalle developed a deep interest in differential equations through his interaction with Solomon Lefschetz and

Richard Bellman Richard Ernest Bellman (August 26, 1920 – March 19, 1984) was an American applied mathematician, who introduced dynamic programming in 1953, and made important contributions in other fields of mathematics, such as biomathematics. He founde ...

, with whom he developed a close friendship. From 1958 until 1964 LaSalle was based at the

Research Institute for Advanced Studies The Baltimore-based Research Institute for Advanced Studies (RIAS), not to be confused with the better-known Institute for Advanced Study in Princeton, New Jersey, was among the several centers for research in the mathematical and physical science ...

(RIAS) in

Baltimore Baltimore ( , locally: or ) is the most populous city in the U.S. state of Maryland, fourth most populous city in the Mid-Atlantic, and the 30th most populous city in the United States with a population of 585,708 in 2020. Baltimore was d ...

, where he worked closely with Lefschetz and in 1960 published his extension of Lyapunov stability theory, known today as

. In 1962-1963 he was President of the

Society for Industrial and Applied Mathematics Society for Industrial and Applied Mathematics (SIAM) is a professional society dedicated to applied mathematics, computational science, and data science through research, publications, and community. SIAM is the world's largest scientific socie ...

(SIAM) and was a member of its board of trustees in 1964–1967. In 1964 LaSalle founded the

Journal of Differential Equations A journal, from the Old French ''journal'' (meaning "daily"), may refer to: *Bullet journal, a method of personal organization *Diary, a record of what happened over the course of a day or other period *Daybook, also known as a general journal, a ...

Journal of Differential Equations Editorial Board
/ref> and served as its Editor-in-Chief until 1980. In 1964 he became the first director of the Center for Dynamical Systems at

Brown University Brown University is a private research university in Providence, Rhode Island. Brown is the seventh-oldest institution of higher education in the United States, founded in 1764 as the College in the English Colony of Rhode Island and Providenc ...

, where he was also the chairman of the Division of Applied Mathematics in 1968–1973.Center for Dynamical Systems at Brown University
/ref> Together with J. K. Hale, LaSalle was the recipient of the 1965

Chauvenet Prize The Chauvenet Prize is the highest award for mathematical expository writing. It consists of a prize of $1,000 and a certificate, and is awarded yearly by the Mathematical Association of America in recognition of an outstanding expository article ...

for their article, ″''Differential Equations: Linearity vs. Nonlinearity''″, published in the SIAM Review.Mathematical Association of America, Chauvenet Prize recipients
/ref> In 1975 he was awarded the

Guggenheim Fellowship Guggenheim Fellowships are grants that have been awarded annually since by the John Simon Guggenheim Memorial Foundation to those "who have demonstrated exceptional capacity for productive scholarship or exceptional creative ability in the ar ...

for applied mathematics.Joseph P. LaSalle Guggenheim Fellowship, 1975
/ref>

Works

;Books * * * * ;Articles * * * * Bellman, R.E., LaSalle, J.P. ''On Non-Zero-Sum Games and Stochastic Processes'', Project RAND Research Memorandum, RM-212, 19 August 1949.
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* Bellman, R.E., Blackwell, D., LaSalle, J.P. ''Application of Theory of Games to Identification of Friend and Foe'', Project RAND Research Memorandum, RM-197, 28 July 1949.
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*LaSalle, J.P. ''Stability theory for ordinary differential equations'',

, volume 4, issue 1, pp. 57–65, 1968.
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*LaSalle, J.P. ''An Invariance Principle in the Theory of Stability'', Brown University, Center for Dynamical Systems, Technical Report 66–1, 1966.
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*LaSalle, J.P. ''Stability and Control'', SIAM Journal of Control, 1962.
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*LaSalle, J.P. ''Recent Advances in Liapunov Stability Theory'', SIAM Review, vol. 6, no. 1, January 1964.
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*LaSalle, J.P. ''The Second International Congress of IFAC on Automatic Control'', SIAM Review, vol 6., no. 3, July 1964.
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References

{{DEFAULTSORT:LaSalle, Joseph P. 1916 births 1983 deaths 20th-century American mathematicians Control theorists California Institute of Technology alumni Brown University faculty University of Notre Dame faculty People from State College, Pennsylvania