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Quantization effects on the equilibrium behavior of combined fuzzy cognitive maps

✍ Scribed by Rod Taber; Ronald R. Yager; Cathy M. Helgason


Publisher
John Wiley and Sons
Year
2006
Tongue
English
Weight
207 KB
Volume
22
Category
Article
ISSN
0884-8173

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✦ Synopsis


Fuzzy cognitive maps ~FCMs! allow experts to express their knowledge by drawing weighted causal digraphs. Experts can pool or fuse their knowledge by adding the underlying FCM causal matrices. This naturally extends the ordered-weighted-averaging ~OWA! technique to averaging dynamical systems and can create complex dynamical systems from several simpler ones. Edge quantization allows experts to state their knowledge in the simpler terms of causal increase ~1!, decrease ~Οͺ1!, or absence ~0!. We model the expert FCMs as a sequence of random fields to study the small-sample effects of quantizing both the causal edges and the fuzzy-set concept nodes. The averaged quantized random matrices exhibit large-sample convergence to the population means of the unquantized matrices in accordance with the Strong Law of Large Numbers. But the small-sample averages can show substantial diversity of equilibrium attractors ~fixed points or limit cycles!. We use statistical tests-chi-square tests, Spearman's rank coefficient, the Kolmogorov-Smirnov test, and the fuzzy equality of limit cycle histograms-to show that this small-sample equilibrium diversity increases as the node multivalence or fuzzy-set quantization increases. The appendix presents a new probabilistic convergence theorem that shows that edge quantization or thresholding does not affect FCM combination for large expert sample sizes: the sample mean of quantized expert causal edge values converges with probability one to the population mean causal edge values.


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