In Memoriam Arie Hordijk
Last week we were informed that Prof. A. Hordijk, emeritus professor at the Mathematical Institute, has passed away. Arie Hordijk (1940) came to the Universiteit Leiden in 1976 and has been a professor of Mathematics of Operations Research at our institute until his retirement in 2005.
Under the leadership of Gijs de Leve, an enthusiastic group of young staff conducted research at the Mathematical Centre (now CWI) in the field of Markov Decision Processes, a then new field within Stochastic Decision Theory.
Arie Hordijk played a prominent role in this with Henk Tijms and Awi Federgruen.
Together with Jaap Wessels' group in Eindhoven, they made the Netherlands one of the world's leading centres in this field.
Arie, Henk Tijms and Jan-Willem Cohen were also the initiators of the Queueing Colloquium that has been held annually at the CWI since 1978, after its start at Utrecht University. In 1980 Arie's work was awarded the Van Dantzig Prize.
Many of Arie's PhD students and former students played and still play a prominent role in Applied Mathematics. His PhD students Frank van der Duijn Schouten, Lodewijk Kallenberg, Nico van Dijk, Rommert Dekker and Ger Koole have become full professors. Ad Ridder, Floske Spieksma and Dinard van der Laan are associate professors, and the three other PhD students Anneke Loeve, Nicolai Popov and Olaf Passchier have entered the business world.
In addition, former student Ton de Kok is the new director of the CWI, and former student Richard Boucherie is a professor in Twente.
The Leiden Math of OR group was a lively international group: Sheldon Ross (known to many students for his books on Stochastic Dynamic Programming and Stochastic Processes) and, after the perestroika, Alexander Borovkov and Alexander Yushkevich were among his guests and co-authors.
There was also room for relaxation: around 1990 an annual sailing trip took place with the group. Arie invariably appeared in a 70s jeans suit.
Besides math, singing was a great passion of Arie. It has sometimes happened that an article by a PhD student was left in a drawer for six months due to a persistent cold of the person concerned. Arie thought the risk of infection and therefore of not being able to sing too big! After his retirement he hoped to be able to devote more attention to the cultural aspects of life. Unfortunately, shortly before, he was diagnosed with Parkinson's disease.
It was typical Arie to not give up! As long as he could, he has published research with, amongst others, Bernd Heidergott and with his cousin Wim Hordijk. He continued to sing, and started to paint and to write poetry!
Frank van der Duijn Schouten