Closing the Gap Between Theory and Practice: New Measures for On-Line Algorithm Analysis

We compare the theory and practice of online algorithms, and show that in certain instances there is a large gap between the predictions from theory and observed practice. In particular, the competitive ratio which is the main technique for analysis of online algorithms is known to produce unrealistic measures of performance in certain settings. Motivated by this we examine first the case of paging. We present a study of the reasons behind this apparent failure of the theoretical model. We then show that a new measure derived from first principles and introduced by [Angelopoulos, Dorrigiv and Lopez-Ortiz, SODA 2007] better corresponds to observed practice. Using these ideas, we derive a new framework termed the cooperative ratio that generalizes to all other online analysis settings and illustrate with examples in list update.

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