On the Lovász δ-number of almost regular graphs with application to Erdős-Rényi graphs
European Journal of Combinatorics
Expressing combinatorial problems by systems of polynomial equations and hilbert's nullstellensatz
Combinatorics, Probability and Computing
On crossing numbers of geometric proximity graphs
Computational Geometry: Theory and Applications
An iterative scheme for valid polynomial inequality generation in binary polynomial programming
IPCO'11 Proceedings of the 15th international conference on Integer programming and combinatoral optimization
Journal of Global Optimization
The 2-page crossing number of Kn
Proceedings of the twenty-eighth annual symposium on Computational geometry
A branch-and-cut approach to the crossing number problem
Discrete Optimization
Using symmetry to optimize over the sherali-adams relaxation
ISCO'12 Proceedings of the Second international conference on Combinatorial Optimization
Zarankiewicz's Conjecture is finite for each fixed m
Journal of Combinatorial Theory Series B
Exploiting Symmetries in SDP-Relaxations for Polynomial Optimization
Mathematics of Operations Research
Book drawings of complete bipartite graphs
Discrete Applied Mathematics
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We consider semidefinite programming problems on which a permutation group is acting. We describe a general technique to reduce the size of such problems, exploiting the symmetry. The technique is based on a low-order matrix $$*$$-representation of the commutant (centralizer ring) of the matrix algebra generated by the permutation matrices. We apply it to extending a method of de Klerk et al. that gives a semidefinite programming lower bound to the crossing number of complete bipartite graphs. It implies that cr(K 8,n ) ≥ 2.9299n 2 − 6n, cr(K 9,n ) ≥ 3.8676n 2 − 8n, and (for any m ≥ 9) $$\lim_{n\to\infty}\frac{{\rm cr}(K_{m,n})}{Z(m,n)}\geq 0.8594\frac{m}{m-1},$$ where Z(m,n) is the Zarankiewicz number $$\lfloor\frac{1}{4}(m-1)^2\rfloor\lfloor\frac{1}{4}(n-1)^2\rfloor$$, which is the conjectured value of cr(K m,n). Here the best factor previously known was 0.8303 instead of 0.8594.