Beat Gfeller

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Peter Widmayer22
Nicola Santoro12
Guido Proietti11
Christian Lavault10
Franck Butelle10
12Peter Widmayer
6Elias Vicari
6Nicola Santoro
5Nitesh Saxena
5Gaurav Kanade

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Towards Optimal Range Medians
We consider the following problem: Given an unsorted array of n elements, and a sequence of intervals in the array, compute the median in each of the subarrays defined by the intervals. We describe a simple algorithm which needs O(n log k + k log n) time to answer k such median queries. This improves previous algorithms by a logarithmic factor and matches a… (More)
Angle Optimization in Target Tracking
We consider the problem of tracking n targets in the plane using 2n cameras, where tracking each target requires two distinct cameras. A single camera (modeled as a point) sees a target point in a certain direction, ideally with unlimited precision, and thus two cameras (not collinear with the target) unambiguously determine the position of the target. In… (More)
Identifying refactoring opportunities in process model repositories
Context: In order to ensure high quality of a process model repository, refactoring operations can be applied to correct anti-patterns, such as overlap of process models, inconsistent labeling of activities and overly complex models. However, if a process model collection is created and maintained by different people over a longer period of time, manual… (More)
A randomized distributed algorithm for the maximal independent set problem in growth-bounded graphs
The efficient distributed construction of a maximal independent set (MIS) of a graph is of fundamental importance. We study the problem in the class of Growth-Bounded Graphs, which includes for example the well-known Unit Disk Graphs. In contrast to the fastest (time-optimal) existing approach [11], we assume that no geometric information (e.g., distances… (More)
Counting Targets with Mobile Sensors in an Unknown Environment
We consider the problem of counting the number of indistinguishable targets using a simple binary sensing model. Our setting includes an unknown number of point targets in a (simply-or multiply-connected) polygonal workspace, and a moving point-robot whose sensory input at any location is a binary vector representing the cyclic order of the polygon vertices… (More)
A Distributed Algorithm for Finding All Best Swap Edges of a Minimum-Diameter Spanning Tree
Communication in networks suffers if a link fails. When the links are edges of a tree that has been chosen from an underlying graph of all possible links, a broken link even disconnects the network. Most often, the link is restored rapidly. A good policy to deal with this sort of transient link failures is swap rerouting, where the temporarily broken link… (More)
A Faster Distributed Approximation Scheme for the Connected Dominating Set Problem for Growth-Bounded Graphs
We present a distributed algorithm for finding a (1 + ε)-approximation of a Minimum Connected Dominating Set in the class of Growth-Bounded graphs, which includes Unit Disk graphs. In addition, the computed Connected Dominating Set guarantees a constant stretch factor on the length of a shortest path with respect to the original graph and induces a subgraph… (More)
Faster Swap Edge Computation in Minimum Diameter Spanning Trees
In network communication systems, frequently messages are routed along a minimum diameter spanning tree (MDST) of the network, to minimize the maximum travel time of messages. When a transient failure disables an edge of the MDST, the network is disconnected, and a temporary replacement edge must be chosen, which should ideally minimize the diameter of the… (More)