# In Memoriam: Heinz-Otto Kreiss

The department is sad to announce that Professor Emeritus Heinz-Otto Kreiss, passed away on Wednesday, December 16th. He died peacefully in his home without pain or anxiety.

**Heinz-Otto Kreiss**

**1930-2015**

One of the great figures in numerical analysis and applied partial differential equations passed away December 16, 2015 at his home in Stockholm. Heinz, as everyone called him, was a faculty member in the Department from 1987-2001 but this fact understates his influence on UCLA’s Applied Mathematics Group.

He was born in Hamburg, Germany, lived and worked on a farm during the war, and became an undergraduate in Hamburg in 1950. In 1955 he went to Stockholm, Sweden where he began his stellar research career. He was a Professor at the Chalmers Institute of Technology in Gothenberg from 1964-65, Uppsala University from 1965-78, Caltech from 1978-1987, and here from 1987-2001, when he retired and returned to Sweden.

Heinz visited the Courant Institute in the 60’s quite often and I was lucky enough to meet him in 1966. This meeting changed my research direction. He had just proven stability of finite difference approximations to hyperbolic equations in one space dimension with the appropriate numerical boundary conditions. I then came up with an elegant proof involving Toeplitz matrices after reading his paper. This got me a job at UC Berkeley and started my career in applied mathematics.

Heinz was a terrific, no nonsense mathematician, with an uncanny ability to get sharp estimates, usually involving families of matrices depending on parameters. There is the Kreiss matrix theorem, stability of difference approximation to hyperbolic equations, well-posedness of initial-boundary value problems for these equations, problems with different time scales, many results on numerical weather prediction and atmospheric science in general and analysis of incompressible Navier-Stokes equation, to name a few of his contributions.

He was also a wonderful and caring human being, who was totally unpretentious (which is not the usual image of a stuffy European professor). For example, when he was inducted into the Swedish Academy of Sciences, the story goes that that he had to borrow a tie and sport jacket from a waiter to get into his dinner and reception. Past and present UCLA faculty members who were influenced by his work include: his Ph.D. student Bjorn Engquist, Andrew Majda, Daniel Michelson, Gregory Eskin, James Ralston, Eitan Tadmor, Moshe Goldberg and myself.

Heinz generated mathematical excitement and enthusiasm and had a charmingly cynical edge at times. He was always fun to be around. He loved his island retreat in Sweden, hated doing university administration, and had an equally wonderful life partner in his wife Barbro, who we all got to know well. His daughter Gunilla is now a Professor in Numerical Analysis at Uppsala University. His scientific legacy lives on. According to the Mathematics Genealogy Project he has 26 students and 463 descendants.

He will be missed by everyone who knew him. He was great, both as a scientist and as a human being.

**Professor Stanley Osher**