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On the rational utilization of the Icelandic cod stock
(1996-08) Baldursson, Friorik M.; Daníelsson, Ásgeir; Stefánsson, Gunnar; Department of Business and Economics
The Icelandic cod stock is analysed with respect to the probable effects of different harvesting strategies on yield, spawning stock biomass, and economic benefits. Simulations are used to investigate the probability of stock recovery and collapse. Potential yield and economic benefits/costs are also investigated, using stochastic and deterministic models. In stochastic simulations, attention is paid to the apparent stock recruitment relationship, the highly variable weight-at-age and maturity-at-age in Icelandic water along with the inevitable inaccuracies in current and future assessments. Regardless of method, substantial reduction in catches from recent (1993) levels is seen to be necessary in order to rebuild the stock. In the deterministic model, profit maximization mandates closure of the fishery until stock is rehabilitated. Using the stochastic model, it is predicted that recent catch level lead to eventual extinction of the stock with high probability. A management procedure is formulated and its application to the model is shown to lead to stabilization of the stock around an economically and biologically acceptable level.
Verk
Lower bounds for on-line graph coloring
(Association for Computing Machinery, 1992-09-01) Halldórsson, Magnús M.; Szegedy, Márió; Department of Computer Science
An algorithm for vertex-coloring graphs is said to be online if each vertex is irrevocably assigned a color before any later vertices are considered. We show that such algorithms are inherently ineffective. The performance ratio of any such algorithm can be no better than Ω(n/log2n), even for randomized algorithms against oblivious adversary. We also show that various means of relaxing the constraints of the on-line model do not reduce these lower bounds. The features include presenting the input in blocks of log2 n vertices, recoloring any fraction of the vertices, presorting vertices according to degree, and disclosing the adversary's previous coloring.
Verk
Sibilla : A Tool for Reasoning about Collective Systems
(Springer Science and Business Media Deutschland GmbH, 2022) Del Giudice, Nicola; Matteucci, Lorenzo; Quadrini, Michela; Rehman, Aniqa; Loreti, Michele; ter Beek, Maurice H.; Sirjani, Marjan; Department of Computer Science
Sibilla is a Java framework designed to support the analysis of Collective Adaptive Systems. These are systems composed by a large set of interactive agents that cooperate and compete to reach local and global goals. Sibilla is thought of container where different tools supporting specification and analysis of concurrent and distributed large scaled systems can be integrated. In this paper, a brief overview of Sibilla features is provided together with a simple example showing some of the tool’s practical capabilities.
Verk
Impossible ecologies: Interaction networks and stability of coexistence in ecological communities
(2023) Meng, Y.; Horvát, S.; Modes, C.D.; Haas, P.A.; Department of Computer Science
Verk
Community Detection in Directed Weighted Networks using Voronoi Partitioning
(2023) Molnár, Botond; Márton, Ildikó-Beáta; Horvát, Szabolcs; Ercsey-Ravasz, Mária; Department of Computer Science
Community detection is a ubiquitous problem in applied network analysis, yet efficient techniques do not yet exist for all types of network data. Most techniques have been developed for undirected graphs, and very few exist that handle directed and weighted networks effectively. Here we present such an algorithm based on Voronoi partitionings. As an added benefit, this method can directly employ edge weights that represent lengths, in contrast to algorithms that operate with connection strengths, requiring ad-hoc transformations of length data. We demonstrate the method on inter-areal brain connectivity, air transportation networks, as well as on randomly generated benchmark networks. The algorithm can handle dense graphs where weights are the main factor determining communities. The hierarchical structure of networks can also be detected, as shown for the brain. Its time efficiency is comparable with other state-of-the-art algorithms, the most costly part being Dijkstra's shortest paths algorithm.

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