Browsing by Subject "Approximate solution"

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    Approximate Schur preconditioners for efficient solutions of dielectric problems formulated with surface integral equations
    (IEEE, 2009-07) Malas, Tahir; Gürel, Levent
    We propose direct and iterative versions of approximate Schur preconditioners to increase robustness and efficiency of iterative solutions of dielectric problems formulated with surface integral equations. The performance of these preconditioners depends on the availability of fast and approximate solutions to reduced matrix systems. We show that sparse-approximate-inverse techniques provide a suitable mechanism for this purpose. The proposed preconditioners are demonstrated to significantly improve convergence rates of dielectric problems formulated with two different surface integral equations. ©2009 IEEE.
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    Replacement problem in Web caching
    (IEEE, 2003-06-07) Çakıroğlu, Seda; Arıkan, Erdal
    Caching has been recognized as an effective scheme for avoiding service bottleneck and reducing network traffic in World Wide Web. Our work focuses on the replacement problem in Web caching, which arises due to limited storage. We seek the best configuration for a fully connected network of N caches. The problem is formulated as a discrete optimization problem. A number of low complexity heuristics are studied to obtain approximate solutions. Performances are tested under fictitious probabilistic request sequences access logs of real Web traffic. LFD (longest-forward-distance), the classical optimal off-line paging algorithm, is observed not to be optimal. Instead a window scheme should be used. Under an unchanging request pattern, a simple static placement algorithm achieves the maximum hit rates using the arrival probabilities. Otherwise, for quick adaptation to changing requests and for better worst-case performances a randomized algorithm should be chosen. We also give an analysis of Web data to propose best heuristics for its characteristics. © 2003 IEEE.