Mathematics

  2010 MAR 9 - (VerticalNews.com) -- According to a study from Shenzhen, People's Republic of China, "In this note, we discuss the problem of the sample-path-based (on-line) performance gradient estimation for Markov systems. The existing on-line performance gradient estimation algorithms generally require a standard importance sampling assumption."

  "When the assumption does not hold, these algorithms may lead to poor estimates for the gradients. We show that this assumption can be relaxed and propose algorithms with multi-step sampling for performance gradient estimates; these algorithms do not require the standard assumption," wrote Y.J. Li and colleagues ...read more

  2010 MAR 9 - (VerticalNews.com) -- According to recent research from the United States, "The problem of optimally controlling the processing rate of tasks in Discrete Event Systems with hard real-time constraints has been addressed in prior work under the assumption that a feasible solution exists. Since this cannot generally be the case, we introduce in this paper an admission control scheme in which some tasks are removed with the objective of maximizing the number of remaining tasks which are all guaranteed feasibility. ...read more

  2010 MAR 9 - (VerticalNews.com) -- According to a study from Stockholm, Sweden, "Natural projections with the observer property have proved effective in reducing the computational complexity of nonblocking supervisory control design, and the state sizes of the resulting controllers. In this paper we present an algorithm to verify this property, or if necessary to achieve it."

  "A natural projection is a special type of general causal reporter map; for the latter an algorithm is already known for verification and modification. This algorithm could be used to verify the observer property of a natural projection, but if the natural projection is not an observer the algorithm is not applicable to modify it to an observer. Also, while a general reporter map always admits a unique smallest refinement with the observer property, a natural projection does not. Indeed there may exist several minimal extensions to the original observable event set of a natural projection. We show that the problem of finding a minimal extension is NP-hard, but propose a polynomial-time algorithm that always finds an acceptable extension," wrote L. Feng and colleagues ...read more