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The development and calibration of complex traffic models demands parsimonious techniques, because such models often involve hundreds of thousands of unknown parameters. The Weighted Simultaneous Perturbation Stochastic Approximation (W-SPSA) algorithm has been proven more efficient than its predecessor SPSA (Spall, 1998), particularly in situations where the correlation structure of the variables is not homogeneous. This is crucial in traffic simulation models where effectively some variables (e.g. readings from certain sensors) are strongly correlated, both in time and space, with some other variables (e.g. certain OD flows). In situations with reasonably sized traffic networks, the difference is relevant considering computational constraints. However, W-SPSA relies on determining a proper weight matrix (W) that represents those correlations, and such a process has been so far an open problem, and only heuristic approaches to obtain it have been considered.This paper presents W-SPSA in a formally comprehensive way, where effectively SPSA becomes an instance of W-SPSA, and explores alternative approaches for determining the matrix W. We demonstrate that, relying on a few simplifications that marginally affect the final solution, we can obtain W matrices that considerably outperform SPSA. We analyse the performance of our proposed algorithm in two applications in motorway networks in Singapore and Portugal, using a dynamic traffic assignment model and a microscopic traffic simulator, respectively. 相似文献
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宋岩 《南通航运职业技术学院学报》2010,9(1):50-53
本文以Z6150ZLCZ-5型柴油机为对象,阐明了船用柴油机排放台架试验的试验要求、主要仪器、台架布置和试验结果,为船用柴油机满足排放标准拓宽思路。 相似文献
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从轨道衡地点选定、线路要求、机械台而、电气设备等方面介绍不断轨动态称量轨道衡安装各阶段、过程的方法与指引,以及轨道衡的计量检定。 相似文献
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介绍了无核密度仪的测试原理,针对Superpave-25型沥青混合料,对无核密度仪基于不同测定样本容量的标定方法进行了比较分析,证明了提高测定样本容量标定的无核密度仪用于Superpave-25型沥青混凝土面层密度测定是可行和可靠的。同时,基于密度差的离析判别标准,采用无核密度仪评价沥青混凝土路面内部施工离析,并提出了控制施工离析的建议措施。 相似文献