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We investigated the phenomenon of activity cycles in ants, taking into account the spatial structure of colonies. In our study species, Leptothorax acervorum, there are two spatially segregated groups in the nest. We developed a model that considers the two groups as coupled oscillators which can produce synchronized activity. By investigating the e¡ects of(More)
Quadratic pencils arising from applications are often inherently structured. Factors contributing to the structure include the connectivity of elements within the underlying physical system and the mandatory nonnegativity of physical parameters. For physical feasibility, structural constraints must be respected. Consequently, they impose additional(More)
In this paper we consider methods for evaluating both exp(A) and exp(τA)q1 where exp(·) is the exponential function, A is a sparse skew-symmetric matrix of large dimension, q1 is a given vector, and τ is a scaling factor. The proposed method is based on two main steps: A is factorized into its tridiagonal form H by the well-known Lanczos iterative process,(More)
In various applications, data in multi-dimensional space are normalized to unit length. This paper considers the problem of best fitting given points on the m-dimensional unit sphere S m−1 by k-dimensional great circles with k much less than m. The task is cast as an algebraically constrained low-rank matrix approximation problem. Using the fidelity of the(More)
Non-negative dyadic data, that is data representing observations which relate two finite sets of objects, appear in several domain applications, such as text-mining-based information retrieval, collaborative filtering and recommender systems, micro-array analysis and computer vision. Discovering latent subgroups among data is a fundamental task to be(More)