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On the nonexistence of pseudo-generalized quadrangles
European Journal of Combinatorics ( IF 1.0 ) Pub Date : 2020-05-28 , DOI: 10.1016/j.ejc.2020.103128
Ivan Guo , Jack H. Koolen , Greg Markowsky , Jongyook Park

In this paper, we consider the question of when a strongly regular graph with parameters ((s+1)(st+1),s(t+1),s1,t+1) can exist. A strongly regular graph with such parameters is called a pseudo-generalized quadrangle. A pseudo-generalized quadrangle can be derived from a generalized quadrangle, but there are other examples which do not arise in this manner. If the graph is derived from a generalized quadrangle then ts2 and st2, while for pseudo-generalized quadrangles we still have the former bound but not the latter. Previously, Neumaier has proved a bound for s which is cubic in t, but we improve this to one which is quadratic. The proof involves a careful analysis of cliques and cocliques in the graph. This improved bound eliminates many potential parameter sets which were otherwise feasible.



中文翻译:

关于伪广义四边形的不存在

在本文中,我们考虑以下问题:何时带有参数的强正则图 s+1个sŤ+1个sŤ+1个s-1个Ť+1个可以存在。具有此类参数的强正则图称为伪广义四边形。伪广义四边形可以从广义四边形派生,但是还有其他一些示例未以这种方式出现。如果图是从广义四边形得出的,则Ťs2sŤ2,而对于伪广义四边形,我们仍然具有前者约束,而没有后者。以前,诺伊麦尔(Neumaier)已经证明了s 这是立方的 Ť,但我们将其改进为二次方。证明包括仔细分析图中的集团和同伴。这种改进的界限消除了许多可能可行的潜在参数集。

更新日期:2020-05-28
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