17 research outputs found
Nonexistence of Certain Skew-symmetric Amorphous Association Schemes
An association scheme is amorphous if it has as many fusion schemes as
possible. Symmetric amorphous schemes were classified by A. V. Ivanov [A. V.
Ivanov, Amorphous cellular rings II, in Investigations in algebraic theory of
combinatorial objects, pages 39--49. VNIISI, Moscow, Institute for System
Studies, 1985] and commutative amorphous schemes were classified by T. Ito, A.
Munemasa and M. Yamada [T. Ito, A. Munemasa and M. Yamada, Amorphous
association schemes over the Galois rings of characteristic 4, European J.
Combin., 12(1991), 513--526]. A scheme is called skew-symmetric if the diagonal
relation is the only symmetric relation. We prove the nonexistence of
skew-symmetric amorphous schemes with at least 4 classes. We also prove that
non-symmetric amorphous schemes are commutative.Comment: 10 page
Detecting anomalies in heterogeneous population-scale VAT networks
Anomaly detection in network science is the method to determine aberrant
edges, nodes, subgraphs or other network events. Heterogeneous networks
typically contain information going beyond the observed network itself. Value
Added Tax (VAT, a tax on goods and services) networks, defined from pairwise
interactions of VAT registered taxpayers, are analysed at a population-scale
requiring scalable algorithms. By adopting a quantitative understanding of the
nature of VAT-anomalies, we define a method that identifies them utilising
information from micro-scale, meso-scale and global-scale patterns that can be
interpreted, and efficiently implemented, as population-scale network analysis.
The proposed method is automatable, and implementable in real time, enabling
revenue authorities to prevent large losses of tax revenues through performing
early identification of fraud within the VAT system.Comment: 14 pages, 5 figures, 3 table