Guest editorial: foreword to the special issue on aggregation operators

The fourteen papers in this special section are devoted to aggregation operators with respect to knowledge based systems.

Fitting aggregation operators to data

Theoretical advances in modelling aggregation of information produced a wide range of aggregation operators, applicable to almost every practical problem. The most important classes of aggregation operators include triangular norms, uninorms, generalised means and OWA operators.
With such a variety, an important practical problem has emerged: how to fit the parameters/ weights of these families of aggregation operators to observed data? How to estimate quantitatively whether a given class of operators is suitable as a model in a given practical setting? Aggregation operators are rather special classes of functions, and thus they require specialised regression techniques, which would enforce important theoretical properties, like commutativity or associativity. My presentation will address this issue in detail, and will discuss various regression methods applicable specifically to t-norms, uninorms and generalised means. I will also demonstrate software implementing these regression techniques, which would allow practitioners to paste their data and obtain optimal parameters of the chosen family of operators.

Pointwise construction of Lippschitz aggregation operators with specific properties

This paper describes an approach to pointwise construction of general aggregation operators, based on monotone Lipschitz approximation. The aggregation operators are constructed from a set of desired values at certain points, or from empirically collected data. It establishes tight upper and lower bounds on Lipschitz aggregation operators with a number of different properties, as well as the optimal aggregation operator, consistent with the given values. We consider conjunctive, disjunctive and idempotent n-ary aggregation operators; p-stable aggregation operators; various choices of the neutral element and annihilator; diagonal, opposite diagonal and marginal sections; bipolar and double aggregation operators. In all cases we provide either explicit formulas or deterministic numerical procedures to determine the bounds. The findings of this paper are useful for construction of aggregation operators with specified properties, especially using interpolation schemata.

Interpolatory type construction of general aggregation operators

In this chapter we examine a number of methods to construct aggregation operators of interpolatory type for specific applications. The construction is based on the desired values of the aggregation operator at certain prototypical points, and on other desired properties, such as, conjuctive, disjunctive or averaging behaviour, symmetry and marginals.

Identification of weights in aggregation operators

This chapter provides a review of various techniques for identification of weights in generalized mean and ordered weighted averaging aggregation operators, as well as identification of fuzzy measures in Choquet integral based operators. Our main focus is on using empirical data to compute the weights. We present a number of practical algorithms to identify the best aggregation operator that fits the data.

Texture recognition by using GLCM and various aggregation functions

We discuss the problem of texture recognition based on the grey level co-occurrence matrix (GLCM). We performed a number of numerical experiments to establish whether the accuracy of classification is optimal when GLCM entries are aggregated into standard metrics like contrast, dissimilarity, homogeneity, entropy, etc., and compared these metrics to several alternative aggregation methods.We conclude that k nearest neighbors classification based on raw GLCM entries typically works better than classification based on the standard metrics for noiseless data, that metrics based on principal component analysis inprove classification, and that a simple change from the arithmetic to quadratic mean in calculating the standard metrics also improves classification.

Towards co-design with users who have autism spectrum disorders

People with cognitive disorders, such as autism or Asperger’s syndrome, face many barriers when being involved in the co-design of information and communications technologies (ICT). Cognitive disorders may require that co-design techniques be modified to fit with individual abilities. Up until recently, with technology design, purpose and use being in the hands of ‘experts’ there was little opportunity for customisation. However, ICT bring together various threads that make open many new possibilities. Not only are technologies cheaper, more powerful and more available than ever, but now parents, support agencies and people with autism spectrum disorders expect information technologies to be part of their worlds, and they have the capacity to participate in co-design for customisation. However, co-design techniques have not evolved to the extent that they capture this potential democratisation of the ICT. This paper reports on an investigation of the potential to develop a set of guidelines for co-design techniques to enable people with autism spectrum disorders to participate in ICT design.

Inhibition of platelet aggregation by omega-3 polyunsaturated fatty acids is gender specific — redefining platelet response to fish oils

Existence of gender differences in cardiovascular disease (CVD) following long-chain omega-3 polyunsaturated fatty acid (LCn-3 PUFA) supplementation have suggested that sex hormones play a role in cardio-protection. The objective of this study was to determine gender specific responses in the efficacy of LCn-3 PUFA to inhibit platelet aggregation in vitro. Blood was analyzed for collagen-induced platelet aggregation following pre-incubation with LCn-3 PUFA in healthy adults (n=42). Eicosapentaenoic acid (EPA) was significantly more effective in reducing platelet aggregation compared with docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). When grouped by gender, this differential pattern was followed in males only. In females, DHA, DPA and EPA were all equally effective. Between group analyses (LCn-3 PUFA vs. gender) showed that both DHA and DPA were significantly less effective in males compared with females. EPA was equally effective in reducing platelet aggregation in both groups. These findings show that significant gender differences exist in platelet aggregation in response to various LCn-3 PUFA treatments.

Environmental variation and the maintenance of polymorphism : the effect of ambient light spectrum on mating behaviour and sexual selection in guppies

The intensity of sexual selection is influenced by environmental conditions because these conditions influence signal propagation and the risks of the signal being exploited by predators and parasites. We explore the possibility that spatial or temporal heterogeneity in environmental signalling conditions (in this case light spectrum) may induce fluctuating sexual selection on male behaviour and ornamentation in guppies. We used shade cloth and filters to experimentally manipulate light spectrum, mimicking conditions found naturally: early morning/late afternoon light (SC treatment), midday forest shade (F89 filter treatment) and midday woodland shade (F55 filter treatment). Females were more responsive to male courtship and males were less likely to attempt sneak copulations under F55 light than the other two treatments. By contrast, male display rate was not influenced by treatment. Females tended to prefer the same males under SC and F55 light, but attractiveness in these treatments was unrelated to attractiveness under F89 light. There were similarities among treatments in the traits that females preferred: females preferred males with larger areas of orange in all three treatments. There were, however, also some differences, including preference for larger males under F89 light and for smaller males under the other treatments. Overall, the influence of ambient light spectrum on the relative importance of mate choice and male sneak copulation may have important implications for the mode and strength of sexual selection in different environments. The findings on attractiveness and preference functions, however, suggest that light spectrum only weakly affects the direction of sexual selection by female choice.

Construction of aggregation functions from data using linear programming

This article examines the construction of aggregation functions from data by minimizing the least absolute deviation criterion. We formulate various instances of such problems as linear programming problems. We consider the cases in which the data are provided as intervals, and the outputs ordering needs to be preserved, and show that linear programming formulation is valid for such cases. This feature is very valuable in practice, since the standard simplex method can be used.