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A simple iterative technique, which is free of certain shortcomings of the previous methods, is proposed for the approximation of large linear systems by a lower- order model. Here, the measure of the goodness of the approximate model is taken to be the value of the integral-square error between the step responses of the exact and the simplified systems. The proposed technique consists of a two-step iterative scheme. In the first step, the optimum residues are obtained by the minimization of the objective function, while the poles (or eigenvalues) are kept constant. In the second step, the poles are optimized while the residues remain fixed. This procedure is continued cyclically until the objective function is satisfactorily minimized. The necessary and sufficient conditions for existence of an optimum are satisfied in each step. The residues, poles and objective functions converge monotonically. The resulting reduced-order model obtained by this method is stable if the original system is stable. The method can also be applied to systems with repeated poles and to multivariable systems. The results are superior to those obtained previously in the steady-state, the point-by-point transient response, and the value of the integral-square error. Illustrative examples are presented. 相似文献
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Margo A. Mastropieri Thomas Scruggs Lisa Mohler Marcia Beranek Vicky Spencer Richard T. Boon Elizabeth Talbott 《Learning disabilities research & practice》2001,16(1):18-27
This investigation was intended to examine the effects of teaching middle school students with learning disabilities and mild mental retardation to tutor one another in reading comprehension strategies. All students were reading significantly below grade level and many students exhibited behavior problems in addition to their primary disability area. Students were randomly assigned to a tutoring or traditional reading instruction condition. Within the tutoring condition, students were matched into tutoring dyads, trained in the tutoring procedures, and taught specific reading comprehension strategies. Reciprocal tutoring was employed, such that students assumed roles of both tutor and tutee during daily reading periods. Performance on reading comprehension tests following tutoring yielded significant performance advantages for students involved in tutoring. Observational, survey, and interview data revealed that students enjoyed tutoring more than their traditional instruction, appeared to see the value and benefits of the tutoring, and wanted to include tutoring as part of their other classes, such as science and social studies. Findings are discussed with respect to the strengths and challenges associated with the use of tutoring to provide strategic instruction to students with special learning needs. 相似文献
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A recursive nonlinear filter and tracking methodology is developed here for a class of partially observable processes. The method is based on an approximation of a nonlinear system by a system which is linear in the unobservable states and has the unobservables conditionally Gaussian with respect to the observations initially. Model smoothness, such as required with most approximating filters is not required here, and applications to simulated tracking problems show the filter to be considerably more accurate than the modified second-order filter which in general sense includes the extended Kalman filter. 相似文献
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