Title: Constant-Work-Space Algorithm for Geometric Problems
Speaker: Tetsuo Asano
School of Information Science
Japan Advanced Institute of Science and Technology

I will talk about space-efficient algorithms for geometric problems in a restricted computational model called ``constant work space'' or ``log-space'' computation. I start with an algorithm for drawing a Delaunay triangulation of a planar point set and then extend it to another algorithm for drawing a Voronoi diagram. There are $\Theta(n \log n)$-time algorithms for those problems in a standard computational model for $n$ points. Our algorithms run in $O(n2)$ time using only a constant number of storage cells of $O(\log n)$ bits in total. Then, I will give a cubic-time algorithm for computing a Euclidean minimum spanning tree for a point set. The fourth problem is to find a simple path between two arbitrary nodes in a tree of $n$ nodes. Our algorithm runs in $O(n^{1+\epsilon})$ time using work space of size $O(1/\epsilon)$ for any small constant $\epsilon > 0$. Then, I will describe how to compute a shortest path between two points in a simple $n$-gon. Although the shortest path problem in general graphs is NL-complete, this constrained problem can be solved in quadratic time using only constant work space.


Dr. Tetsuo Asano was born in Kyoto Prefecture, Japan, in 1949. He got B.E., M.E., and Ph.D degrees from Osaka University, Japan, in 1972, 1974, and 1977, respectively. In 1977 he joined Osaka Electro-Communication University as a lecturer and moved to JAIST (Japan Advanced Institute of Science and technology) in 1997. He is now a professor in School of Information Science. He served as a Presidential Advisor in 1999-2000 and as a senetor in 2001-2003. His research interest includes algorithms and data structures, especially in computational geometry, combinatorial optimization, computer graphics, computer vision using geometric information, and VLSI layout design. He has been serving as editors of several journals including Discrete and Computational Geometry, Computational Geometry: Theory and Applications, International Journal of Computational Geometry and Applications, and Theory of Computing Sysytems. He has contributed to ACM Annual Symposium on Computational Geometry as a program committee member in 1990, 1994, 1996, 2004, and 2010. He served as a chair of a Special Interest Group on Algorithms of Information Processing Society of Japan in 1994-1996. He is fellows of Association of Computing Machinery (2001) and Information Processing Soceity of Japan (2004). Currently he is a director of Center for Graduate Education Initiative.