In this paper, we classify finite 2-groups with a unique minimal non-abelian subgroup of index 2. We also classify finite 2-groups with a 2-generator abelian subgroup of index 2. This paper is a part of classification of finite p-groups with a minimal non-abelian subgroup of index p. Together with our previous work, we solved completely a problem proposed by Y. Berkovich.
Purpose -This paper attempts to extend classic absolute degree of grey incidence so that the extended model can be used for grey number sequences. Design/methodology/approach -The classic absolute degree of grey incidence was extended according to basic principles of grey incidence analysis. First, modelling methods and theories of the classic grey incidences were summarized. Then, the zeroing starting operator in grey incidence was extended for grey sequence. Third, the parameters in classic incidence degree were redefined, and an absolute degree of grey incidence for grey number sequences was proposed. The degree can not only be applied to grey number sequence, but also contains the uncertain information of analysis result. Fourth, two non-linear programming models were constructed to estimate the grey coverage interval of absolute degree of incidences. Finally, the comparison method of grey numbers was introduced for sorting the different absolute degrees of incidences. Findings -A theoretically feasible absolute degree of grey incidence was constructed for grey sequence. A case study showed that the proposed incidence degree was an effective method for grey sequence incidence analysis. Practical implications -The method exposed in the paper can be used for grey sequences clustering, grey decision making, multi-attribute decision making theory, uncertain target recognition and other related fields. Originality/value -The paper succeeded in establishing an incidence analysis model for grey sequences which was still a research gap in grey system theory.
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