Peter Widmayer

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The Web-based software tool Genevestigator provides powerful tools for biologists to explore gene expression across a wide variety of biological contexts. Its first releases, however, were limited by the scaling ability of the system architecture, multiorganism data storage and analysis capability, and availability of computationally intensive analysis(More)
In a variety of applications, we need to keep track of the development of a data set over time. For maintaining and querying these multiversion data efficiently, external storage structures are an absolute necessity. We propose a multiversion B-tree that supports insertions and deletions of data items at the current version and range queries and exact match(More)
We present an algorithm for finding a Steiner tree for a connected, undirected distance graph with a specified subset S of the set of vertices V. The set V-S is traditionally denoted as Steiner vertices. The total distance on all edges of this Steiner tree is at most 2(1−1/l) times that of a Steiner minimal tree, where l is the minimum number of leaves in(More)
In this paper we study the problem of gathering in the same location of the plane a collection of identical oblivious mobile robots. Previous investigations have focused mostly on the unlimited visibility setting, where each robot can always see all the other ones, regardless of their distance. In the more difficult and realistic setting where the robots(More)
We propose the Local Split Decision tree (LSD tree, for short), a data structure supporting efficient spatial access to geometric objects. Its main advantages over other structures are that it performs well for all reasonable data distributions, cover quotients (which measure the overlapping of the data objects), and bucket capacities, and that it maintains(More)
We are given a two-dimensional square grid of size N N, where N := 2 n and n 0. A space lling curve (SFC) is a numbering of the cells of this grid with numbers from c + 1 to c + N 2 , for some c 0. We call a SFC recursive (RSFC) if it can be recursively divided into four square RSFCs of equal size. Examples of well-known RSFCs include the Hilbert curve, the(More)
Databases are growing steadily, and distributed computer systems are more and more easily available. This provides an opportunity to satisfy the increasingly tighter efficiency requirements by means of distributed data structures. The design and analysis of these structures under efficiency aspects, however, has not yet been studied sufficiently. To our(More)
The distributed coordination and control of a set of autonomous mobile robots is a problem widely studied in a variety of fields, such as engineering, artificial intelligence, artificial life, robotics. Generally, in these areas the problem is studied mostly from an empirical point of view. In contrast, we aim to understand the fundamental limitations on(More)