Fitting Aggregation Functions to Data: Part II - Idempotization

The use of supervised learning techniques for fitting weights and/or generator functions of weighted quasi-arithmetic means - a special class of idempotent and nondecreasing aggregation functions - to empirical data has already been considered in a number of papers. Nevertheless, there are still some important issues that have not been discussed in the literature yet. In the second part of this two-part contribution we deal with a quite common situation in which we have inputs coming from different sources, describing a similar phenomenon, but which have not been properly normalized. In such a case, idempotent and nondecreasing functions cannot be used to aggregate them unless proper preprocessing is performed. The proposed idempotization method, based on the notion of B-splines, allows for an automatic calibration of independent variables. The introduced technique is applied in an R source code plagiarism detection system.