25 research outputs found

    Perfect Octagon Quadrangle Systems with an upper C4-system and a large spectrum

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    An octagon quadrangle is the graph consisting of an 8-cycle (x1, x2,..., x8) with two additional chords: the edges {x1, x4} and {x5, x8}. An octagon quadrangle system of order Ī½ and index Ī» [OQS] is a pair (X,H), where X is a finite set of Ī½ vertices and H is a collection of edge disjoint octagon quadrangles (called blocks) which partition the edge set of Ī»KĪ½ defined on X. An octagon quadrangle system Ī£=(X,H) of order Ī½ and index Ī» is said to be upper C4-perfect if the collection of all of the upper 4-cycles contained in the octagon quadrangles form a Ī¼-fold 4-cycle system of order Ī½; it is said to be upper strongly perfect, if the collection of all of the upper 4-cycles contained in the octagon quadrangles form a Ī¼-fold 4-cycle system of order Ī½ and also the collection of all of the outside 8-cycles contained in the octagon quadrangles form a Ļ-fold 8-cycle system of order Ī½. In this paper, the authors determine the spectrum for these systems, in the case that it is the largest possible

    ON THE SPECTRUM OF OCTAGON QUADRANGLE SYSTEMS OF ANY INDEX

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    An \emph{octagon quadrangle} is the graph consisting of a length 88 cycle (x1,x2,ā€¦,x8)(x_{1},x_{2},\dots,x_{8}) and two chords, {x1,x4}\{x_{1},x_{4}\} and {x5,x8}\{x_{5},x_{8}\}. An \emph{octagon quadrangle system} of order vv and index Ī»\lambda is a pair (X,B)(X,\mathcal B), where XX is a finite set of vv vertices and B\mathcal B is a collection of octagon quadrangles (called blocks) which partition the edge set of Ī»Kv\lambda K_{v}, with XX as vertex set. In this paper we determine completely the spectrum of octagon quadrangle systems for any index Ī»\lambda, with the only possible exception of v=20v=20 for Ī»=1\lambda=1

    Uniform coloured hypergraphs and blocking sets

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    strongly balanced 4 kite designs nested into oq systems

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    In this paper we determine the spectrum for octagon quadrangle systems [OQS] which can be partitioned into two strongly balanced 4-kitedesigns

    Dualities and collineations of projective and polar spaces and of related geometries

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    Distance-regular graphs

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    This is a survey of distance-regular graphs. We present an introduction to distance-regular graphs for the reader who is unfamiliar with the subject, and then give an overview of some developments in the area of distance-regular graphs since the monograph 'BCN' [Brouwer, A.E., Cohen, A.M., Neumaier, A., Distance-Regular Graphs, Springer-Verlag, Berlin, 1989] was written.Comment: 156 page

    Some contributions to incidence geometry and the polynomial method

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