Professor Patric R. J. Östergård's home page

First things first: My first son was born on March 21, 2001: Picture 1, Picture 2, Picture 3, Picture 4, Picture 5, Picture 6, Picture 7. On November 4, 2001, he is alreday a lot bigger: Picture 1.

My second son was born on March 21, 2004. The question of the day: Have you already seen this date on this page? Well, his father is a mathematician, isn't he ;-) Second son and Family.

Research interests

• Mathematical objects
  • Codes (covering codes, error-correcting codes, etc.)
  • Combinatorial designs
  • Other structures that can be viewed as packings or coverings
• Combinatorial algorithms
  • Stochastic optimization methods, local search algorithms (tabu search)
  • Exact algorithms for (NP-)hard problems
  • Graph algorithms for clique and coloring problems
  • Algorithms for isomorphism testing; classification algorithms
• Information theory, in general
• Discrete mathematics, in general

Recent and old news

There are 1,054,163 Steiner quadruple systems of order 16; this result has been obtained in joint work with Petteri Kaski and Olli Pottonen.

There exists no Steiner quintuple system of order 17.

There are 11,084,874,829 Steiner triple systems of order 19; see a paper by Petteri Kaski and myself.

Optimal one-error-correcting codes of lengths 10 and 11 have 72 and 144 codewords, respectively; see this page.

There are 5983 perfect binary one-error-correcting codes of length 15; this result, obtained by Olli Pottonen and myself, was submitted in June 2008.

Together with Sampo Niskanen, we have developed Cliquer, routines for clique searching. The first public release (1.0) was made in late 2002; the current release (1.2) can be found here.

I am a recipient of the 1996 Kirkman Medal, awarded by The Institute of Combinatorics and its Applications.

I am co-Editor-in-Chief of the Journal of Combinatorial Designs.

My research is financed in part by the Academy of Finland.

I spent the year 1996 at the Department of Mathematics and Computing Science, Eindhoven University of Technology, the Netherlands.

Publications

The nonexistence of a (K₆-e)-decomposition of the complete graph K₂₉, S. G. Hartke, P. R. J. Östergård, D. Bryant, and S. I. El-Zanati, Journal of Combinatorial Designs, to appear.
Classification of starters, V. Linja-aho and P. R. J. Östergård, Journal of Combinatorial Mathematics and Combinatorial Computing, to appear.
A tournament of order 14 with disjoint Banks and Slater sets, P. R. J. Östergård and V. P. Vaskelainen, Discrete Applied Mathematics, to appear.
Two optimal one-error-correcting codes of length 13 that are not doubly shortened perfect codes, P. R. J. Östergård and O. Pottonen, Designs, Codes and Cryptography, to appear.
A census of one-factorizations of the complete 3-uniform hypergraph of order 9, M. Khatirinejad and P. R. J. Östergård, Australasian Journal of Combinatorics, to appear.
The number of Latin squares of order 11, A. Hulpke, P. Kaski, and P. R. J. Östergård, Mathematics of Computation, to appear.

Other interests