Flag-transitive Steiner Designs (Frontiers in Mathematics) by Michael Huber

By Michael Huber

The monograph presents the 1st complete dialogue of flag-transitive Steiner designs. it is a primary a part of the examine of hugely symmetric combinatorial configurations on the interface of numerous mathematical disciplines, like finite or prevalence geometry, staff thought, combinatorics, coding thought, and cryptography. In a sufficiently self-contained and unified demeanour the class of all flag-transitive Steiner designs is gifted. This contemporary end result settles attention-grabbing and difficult questions which have been item of analysis for greater than forty years. Its facts combines tools from finite team idea, prevalence geometry, combinatorics, and quantity thought. The e-book encompasses a extensive advent to the subject, besides many illustrative examples. additionally, a census of a few of the main normal effects on hugely symmetric Steiner designs is given in a survey bankruptcy. The monograph is addressed to graduate scholars in arithmetic and laptop technology in addition to proven researchers in layout idea, finite or prevalence geometry, coding idea, cryptography, algebraic combinatorics, and extra usually, discrete arithmetic.

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Z Therefore, Φ∗d−1 (2) ≤ z = d. As Φ∗d−1 (2) = 1 has already been considered, we may suppose that Φ∗d−1 (2) = d. 5 (b) yields d ≤ 19. The small number of cases can easily be checked by hand as above. Again, it turns out that only k = 4 can occur. Let us suppose now that k is not a power of 2. We distinguish two cases according to whether or not some non-trivial translation preserves a block B ∈ B. Let TB = 1. Then B is a disjoint union of affine subspaces Xi of AG(d, 2), i ≥ 1 (namely the point-orbits Xi of TB contained in B).

As clearly rank(D) ≤ s, the claim is established. 24 Chapter 4. Highly Symmetric Steiner Designs Tactical decompositions may be applied to get inside the orbit structures of groups of automorphisms of incidence structures. 11. Let D = (X, B, I) be an incidence structure with incidence matrix A of rank |X| over R and G ≤ Aut(D) a group of automorphisms of D. Then, the number of orbits of G on the block set B is at least as large as the number of orbits of G on the point set X. Proof. It can easily be seen that the point and the block orbits of G form a tactical decomposition of A.

5. Let d > 3, and let us assume that G containing P SL(d, q) as simple normal subgroup operates on the projective space P G(d − 1, q) and that for all g ∈ G with |M g ∩ M | ≥ 3 we have M g = M , where M is any set of points of P G(d − 1, q) of cardinality k with 3 ≤ k ≤ |H| and H a hyperplane of P G(d − 1, q). Then, for |M ∩ H| ≥ 3, we have M ∩ H = M . Proof. For k = 3 the assertion is trivial. So, we assume that 3 < k ≤ |H| = q q−1−1 . The set of all translations T (H) form an Abelian group which operates regularly on the points of P G(d − 1, q) \ H by a theorem of Baer, but trivially on H as the central collineations fix each point of H.

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