1,721,123 research outputs found
Food habits and trophic niche overlap of the red fox and the stone marten in a Mediterranean rural area
No full textThe food habits of the red fox Vulpes vulpes (Linnaeus, 1758) and the stone marten Martes foina (Erxleben, 1777) were studied in a rural hilly area in Siena county, central Italy, using faecal analysis. Both frequency of occurrence and volume of the different foods were quantified. Rodents, especially Apodemus sp., were an important prey for both species. Predation on poultry and game birds was nearly absent, whereas fruits and insects were seasonally taken by both species. Rosaceae fruits were the most eaten plant item. Within this category the fox fed mainly on Malus sp. and Pyrus sp., while the marten showed a preference for Rubus sp. and Sorbus domestica. Only fruits of Prunus spinosa were eaten in comparable quantities. Beetles were well represented in the diet of both carnivores, although they tended to concentrate on different species. Grasshoppers were preyed in small quantity. The overall diet overlap of foxes and stone martens was extensive: a surprising result, if the different body size, locomotor adaptations and living habits of these carnivores are considered
Linear Programming
No full textThis chapter provides an introduction to Linear Programming theory. It discusses classical concepts such as duality, complementarity slackness, complexity and algorithmic issues
Activity patterns of the stone marten Martes foina Erxleben, 1777, in relation to some environmental factors
No full textIntroduction
No full textLinear Programming (LP) and Integer Linear Programming (ILP) are two of the most powerful tools ever created in mathematics. Their usefulness comes from the many areas where they can provide satisfactory modeling and solving techniques to real-life problems. Their appeal comes from the rich combinatorial and geometric theory they are based upon. Solving an LP problem consists in minimizing a linear functional over a polyhedron, which, in turn, amounts to detecting a vertex of the polyhedron where the linear functional achieves the minimum (if it exists)
Computational complexity and ilp models for pattern problems in the logical analysis of data
Full text linkLogical Analysis of Data is a procedure aimed at identifying relevant features in data sets with both positive and negative samples. The goal is to build Boolean formulas, represented by strings over {0,1,-} called patterns, which can be used to classify new samples as positive or negative. Since a data set can be explained in alternative ways, many computational problems arise related to the choice of a particular set of patterns. In this paper we study the computational complexity of several of these pattern problems (showing that they are, in general, computationally hard) and we propose some integer programming models that appear to be effective. We describe an ILP model for finding the minimum-size set of patterns explaining a given set of samples and another one for the problem of determining whether two sets of patterns are equivalent, i.e., they explain exactly the same samples. We base our first model on a polynomial procedure that computes all patterns compatible with a given set of samples. Computational experiments substantiate the effectiveness of our models on fairly large instances. Finally, we conjecture that the existence of an effective ILP model for finding a minimum-size set of patterns equivalent to a given set of patterns is unlikely, due to the problem being NP-hard and co-NP-hard at the same time
Scheduling
No full textScheduling problems are notoriously difficult and ILP models have not yet shown adequate strength for them to be competitive with other approaches. This chapter presents a time-indexed model for the Job-Shop problem that can be solved either by column generation or by a compact equivalent formulation. We present also an interesting approach for a one-machine problem for which a Dantzig-Wolfe decomposition was proposed. This example allows us to show how the Dantzig-Wolfe decomposition goes in the opposite direction with respect to the compactification techniques that we have extensively discussed in this book
Cuts and Induced Bipartite Subgraphs
No full textIn this chapter we compare three popular models for the maximum cut problem and show the equivalence of their relaxations by using compact extended formulations. These problems are closely related to the subject of edge-induced and node-induced bipartite subgraphs, for which we give compact extended formulations as well
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