# Mittagsseminar (in cooperation with M. Ghaffari, A. Steger and B. Sudakov)

__Mittagsseminar Talk Information__ | |

**Date and Time**: Tuesday, April 20, 2004, 12:15 pm

**Duration**: This information is not available in the database

**Location**: This information is not available in the database

**Speaker**: Michael Hoffmann (2) (University of Leicester)

## Efficient Update Strategies for Geometric Computing with Uncertainty

We consider the problems of computing maximal points and the
convex hull of a set of points in 2D, when the points are
``in motion.'' We assume that the point locations (or trajectories)
are not known precisely and determining these values exactly is
feasible, but expensive. In our model, the algorithm only knows
areas within which each of the input points lie, and is required
to identify the maximal points or points on the convex hull correctly
by updating some points (i.e. determining exactly their location).
We compare the number of points updated by the algorithm on a given
instance to the minimum number of points that must be updated by a
nondeterministic strategy in order to provably compute the answer
correctly. We give algorithms for both of the above problems that
always update at most 3 times as many points as the nondeterministic
strategy, and show that this is the best possible.

(Joint work with Rajeev Raman and Danny Krizanc)

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