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Wed, 19 Nov 2008 14:30:02 +0100Wed, 19 Nov 2008 14:30:02 +0100A time series model for precipitation based on disaggregation and lognormal point processes
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/2041
In this thesis, we investigate a statistical model for precipitation time series recorded at a single site. The sequence of observations consists of rainfall amounts aggregated over time periods of fixed duration. As the properties of this sequence depend strongly on the length of the observation intervals, we follow the approach of Rodriguez-Iturbe et. al. [1] and use an underlying model for rainfall intensity in continuous time. In this idealized representation, rainfall occurs in clusters of rectangular cells, and each observations is treated as the sum of cell contributions during a given time period. Unlike the previous work, we use a multivariate lognormal distribution for the temporal structure of the cells and clusters. After formulating the model, we develop a Markov-Chain Monte-Carlo algorithm for fitting it to a given data set. A particular problem we have to deal with is the need to estimate the unobserved intensity process alongside the parameter of interest. The performance of the algorithm is tested on artificial data sets generated from the model. [1] I. Rodriguez-Iturbe, D. R. Cox, and Valerie Isham. Some models for rainfall based on stochastic point processes. Proc. R. Soc. Lond. A, 410:269-288, 1987.Nikolaus Rufdoctoralthesishttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/2041Wed, 19 Nov 2008 14:30:02 +0100Set Covering With Almost Consecutive Ones Property
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1448
In this paper we consider set covering problems with a coefficient matrix almost having the consecutive ones property, i.e., in many rows of the coefficient matrix, the ones appear consecutively. If this property holds for all rows it is well known that the set covering problem can be solved efficiently. For our case of almost consecutive ones we present a reformulation exploiting the consecutive ones structure to develop bounds and a branching scheme. Our approach has been tested on real-world data as well as on theoretical problem instances.Nikolaus Ruf; Anita SchÃ¶belpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1448Tue, 11 Nov 2003 14:13:43 +0100