21,337 research outputs found
Products of Borel fixed ideals of maximal minors
We study a large family of products of Borel fixed ideals of maximal minors.
We compute their initial ideals and primary decompositions, and show that they
have linear free resolutions. The main tools are an extension of straightening
law and a very surprising primary decomposition formula. We study also the
homological properties of associated multi-Rees algebra which are shown to be
Cohen-Macaulay, Koszul and defined by a Gr\"obner basis of quadrics
The subdivision of large simplicial cones in Normaliz
Normaliz is an open-source software for the computation of lattice points in
rational polyhedra, or, in a different language, the solutions of linear
diophantine systems. The two main computational goals are (i) finding a system
of generators of the set of lattice points and (ii) counting elements
degree-wise in a generating function, the Hilbert Series. In the homogeneous
case, in which the polyhedron is a cone, the set of generators is the Hilbert
basis of the intersection of the cone and the lattice, an affine monoid.
We will present some improvements to the Normaliz algorithm by subdividing
simplicial cones with huge volumes. In the first approach the subdivision
points are found by integer programming techniques. For this purpose we
interface to the integer programming solver SCIP to our software. In the second
approach we try to find good subdivision points in an approximating overcone
that is faster to compute.Comment: To appear in the proceedings of the ICMS 2016, published by Springer
as Volume 9725 of Lecture Notes in Computer Science (LNCS
Optimal maintenance strategies for systems with partial repair options and without assuming bounded costs
We study a repairable system with Markovian deterioration and partial repair options, carried out at fixed times and look for optimal strategies under certain conditions. Two optimality criteria are considered: expected discounted cost and long-run average cost. Douer and Yechiali found conditions under which a policy in the class of generalized control limit policies is optimal. In this paper conditions are found under which an optimal policy is a control-limit policy. We explicitly explain how to derive this optimal policy; numerical examples are given, too
Citizen journalism in the 2007 Australian Federal Election
Citizen journalists and news and political bloggers are set to have a considerable impact on journalistic coverage of the 2007 Australian federal election campaign. Already, even before the election proper has been called, the alternative viewpoints of citizen journalists and bloggers can be seen to have significantly disrupted the previously relatively static arrangements between government and opposition parties and the journalistic establishment, and to have challenged standard modes of reporting and interpreting political events. This paper discusses the role of citizen journalists and news and political bloggers in the 2007 Australian federal election campaign by examining four key sites of such alternative reporting, analysis, and commentary: the hyperlocal citizen journalism site Youdecide2007.org, the leading left-of-centre political group blog Larvatus Prodeo, the influential psephologist blogger Possums Pollytics, and ABC Onlineâs attempt at blogging the election campaign, The Poll Vault. It analyses the content and style of such initiatives, and tracks the take-up of their work across the wider Australian blogosphere and beyond (in part building on network mapping methodologies as outlined in Bruns, 2007), and on that basis presents an insight into the place of news and political blogging and citizen journalism within the wider Australian mediasphere throughout the federal election campaign
A discounted model for a repairable system with continuous state space
We examine repairable systems with a continous state space and partial repair options, carried out at fixed times . Every time interval there is a manufacturing cost and a repair cost. These cost functions are not restricted to the class of bounded functions in this study. Conditions are found under which a control-limit replacement policy minimizes the discounted cost. Hence these conditions guarantee that there is an optimal policy under the discounted cost criterion which does not use partial repairs. We explicitly explain how to derive this optimal policy
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