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Reduction Problem (reduction + problem)
Kinds of Reduction Problem Selected AbstractsA remark on ,Model reduction for singular systems via covariance approximation'OPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 5 2006Dabo Xu Abstract This note comments on the results of the paper, ,Model reduction for singular systems via covariance approximation', (Optim. Contr. Appl. Meth. 2004; 25:263,278), which studied model reduction for singular system via covariance approximation. Although the proposed new error criterion reflects the capacity of the impulsive behaviour for singular systems, there exists shortcomings due to the fixed matrix Br in the process of optimization, which remarkably matters. In order to avoid this drawback, the model reduction problem is reformulated and a genetic algorithm is used to deal with the optimization problem. A numerical example is provided to show the effectiveness and improvement of the proposed algorithm. Copyright © 2006 John Wiley & Sons, Ltd. [source] An empirical analysis of the relationship between hedge ratio and hedging horizon using wavelet analysisTHE JOURNAL OF FUTURES MARKETS, Issue 2 2007Donald Lien In this article, optimal hedge ratios are estimated for different hedging horizons for 23 different futures contracts using wavelet analysis. The wavelet analysis is chosen to avoid the sample reduction problem faced by the conventional methods when applied to non-overlapping return series. Hedging performance comparisons between the wavelet hedge ratio and error-correction (EC) hedge ratio indicate that the latter performs better for more contracts for shorter hedging horizons. However, the performance of the wavelet hedge ratio improves with the increase in the length of the hedging horizon. This is true for both within-sample and out-of-sample cases. © 2007 Wiley Periodicals, Inc. Jrl Fut Mark 27:127,150, 2007 [source] On ,, model reduction for discrete-time linear time-invariant systems using linear matrix inequalities,ASIAN JOURNAL OF CONTROL, Issue 3 2008Yoshio Ebihara Abstract In this paper, we address the ,, model reduction problem for linear time-invariant discrete-time systems. We revisit this problem by means of linear matrix inequality (LMI) approaches and first show a concise proof for the well-known lower bounds on the approximation error, which is given in terms of the Hankel singular values of the system to be reduced. In addition, when we reduce the system order by the multiplicity of the smallest Hankel singular value, we show that the ,, optimal reduced-order model can readily be constructed via LMI optimization. These results can be regarded as complete counterparts of those recently obtained in the continuous-time system setting. [source] Computationally Efficient Algorithm For Frequency-Weighted Optimal H, Model ReductionASIAN JOURNAL OF CONTROL, Issue 3 2003Fen Wu ABSTRACT In this paper, a frequency-weighted optimal H, model reduction problem for linear time-invariant (LTI) systems is considered. The objective of this class of model reduction problems is to minimize H, norm of the frequency-weighted truncation error between a given LTI system and its lower order approximation. A necessary and sufficient solvability condition is derived in terms of LMIs with one extra coupling rank constraint, which generally leads to a non-convex feasibility problem. Moreover, it has been shown that the reduced-order model is stable when both stable input and output weights are included, and its state-space data are given explicitly by the solution of the feasibility problem. An efficient model reduction scheme based on cone complementarity algorithm (CCA) is proposed to solve the non-convex conditions involving rank constraint. [source] Mechanism of antibody reduction in cell culture production processesBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2010Yung-Hsiang Kao Abstract We recently observed a significant disulfide reduction problem during the scale-up of a manufacturing process for a therapeutic antibody using a CHO expression system. Under certain conditions, extensive reduction of inter-chain disulfide bonds of an antibody produced by CHO cell culture may occur during the harvest operations and/or the protein A chromatography step, resulting in the observation of antibody fragments (light chain, heavy chain, and various combination of both) in the protein A pools. Although all conditions leading to disulfide reduction have not been completely identified, an excessive amount of mechanical cell lysis generated at the harvest step appears to be an important requirement for antibody reduction (Trexler-Schmidt et al., 2010). We have been able to determine the mechanism by which the antibody is reduced despite the fact that not all requirements for antibody reduction were identified. Here we present data strongly suggesting that the antibody reduction was caused by a thioredoxin system or other reducing enzymes with thioredoxin-like activity. The intracellular reducing enzymes and their substrates/cofactors apparently were released into the harvest cell culture fluid (HCCF) when cells were exposed to mechanical cell shear during harvest operations. Surprisingly, the reducing activity in the HCCF can last for a long period of time, causing the reduction of inter-chain disulfide bonds in an antibody. Our findings provide a basis for designing methods to prevent the antibody reduction during the manufacturing process. Biotechnol. Bioeng. 2010;107:622,632. © 2010 Wiley Periodicals, Inc. [source] Generalization of rank reduction problems with Wedderburn's formulaJOURNAL OF CHEMOMETRICS, Issue 11 2003Joan Ferré Abstract In first- and second-order calibration methods based on spectroscopic data, the calculation of the space spanned by the spectra of the interferences has been an important research subject for, among many other applications, calculating the net analyte signal and obtaining figures of merit. Recently, many different calculation methods have been introduced. We show that the calculation of this space can be interpreted from a unified point of view, namely from the rank-one downdating Wedderburn formula. This formula enables one to better understand the properties of the calculation methods currently available. A number of recently introduced signal-preprocessing methods also fit into the proposed framework. Copyright © 2004 John Wiley & Sons, Ltd. [source] Computationally Efficient Algorithm For Frequency-Weighted Optimal H, Model ReductionASIAN JOURNAL OF CONTROL, Issue 3 2003Fen Wu ABSTRACT In this paper, a frequency-weighted optimal H, model reduction problem for linear time-invariant (LTI) systems is considered. The objective of this class of model reduction problems is to minimize H, norm of the frequency-weighted truncation error between a given LTI system and its lower order approximation. A necessary and sufficient solvability condition is derived in terms of LMIs with one extra coupling rank constraint, which generally leads to a non-convex feasibility problem. Moreover, it has been shown that the reduced-order model is stable when both stable input and output weights are included, and its state-space data are given explicitly by the solution of the feasibility problem. An efficient model reduction scheme based on cone complementarity algorithm (CCA) is proposed to solve the non-convex conditions involving rank constraint. [source] | ||||||||||