34,628 research outputs found
Inexactness of the Hydro-Thermal Coordination Semidefinite Relaxation
Hydro-thermal coordination is the problem of determining the optimal economic
dispatch of hydro and thermal power plants over time. The physics of
hydroelectricity generation is commonly simplified in the literature to account
for its fundamentally nonlinear nature. Advances in convex relaxation theory
have allowed the advent of Shor's semidefinite programming (SDP) relaxations of
quadratic models of the problem. This paper shows how a recently published SDP
relaxation is only exact if a very strict condition regarding turbine
efficiency is observed, failing otherwise. It further proposes the use of a set
of convex envelopes as a strategy to successfully obtain a stricter lower bound
of the optimal solution. This strategy is combined with a standard iterative
convex-concave procedure to recover a stationary point of the original
non-convex problem.Comment: Submitted to IEEE PES General Meeting 201
Strategies for Optimize Off-Lattice Aggregate Simulations
We review some computer algorithms for the simulation of off-lattice clusters
grown from a seed, with emphasis on the diffusion-limited aggregation,
ballistic aggregation and Eden models. Only those methods which can be
immediately extended to distinct off-lattice aggregation processes are
discussed. The computer efficiencies of the distinct algorithms are compared.Comment: 6 pages, 7 figures and 3 tables; published at Brazilian Journal of
Physics 38, march, 2008 (http://www.sbfisica.org.br/bjp/files/v38_81.pdf
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