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Near-homogeneous spherical Latin bitrades

Nicholas J. Cavenagh (2013)

Commentationes Mathematicae Universitatis Carolinae

A planar Eulerian triangulation is a simple plane graph in which each face is a triangle and each vertex has even degree. Such objects are known to be equivalent to spherical Latin bitrades. (A Latin bitrade describes the difference between two Latin squares of the same order.) We give a classification in the near-regular case when each vertex is of degree 4 or 6 (which we call a near-homogeneous spherical Latin bitrade, or NHSLB). The classification demonstrates that any NHSLB is equal to two graphs...

New Binary Extremal Self-Dual Codes of Lengths 50 and 52

Buyuklieva, Stefka (1999)

Serdica Mathematical Journal

* This work was partially supported by the Bulgarian National Science Fund under Contract No. MM – 503/1995.New extremal binary self-dual codes of lengths 50 and 52 are constructed. Some of them are the first known codes with such weight enumerators. The structure of their automorphisms groups are shown.

New Symmetric (61,16,4) Designs Invariant Under the Dihedral Group of Order 10

Landjev, Ivan, Topalova, Svetlana (1998)

Serdica Mathematical Journal

∗ This work has been partially supported by the Bulgarian NSF under Contract No. I-506/1995.In this note we construct five new symmetric 2-(61,16,4) designs invariant under the dihedral group of order 10. As a by-product we obtain 25 new residual 2-(45,12,4) designs. The automorphism groups of all new designs are computed.

New Upper Bounds for Some Spherical Codes

Boyvalenkov, Peter, Kazakov, Peter (1995)

Serdica Mathematical Journal

The maximal cardinality of a code W on the unit sphere in n dimensions with (x, y) ≤ s whenever x, y ∈ W, x 6= y, is denoted by A(n, s). We use two methods for obtaining new upper bounds on A(n, s) for some values of n and s. We find new linear programming bounds by suitable polynomials of degrees which are higher than the degrees of the previously known good polynomials due to Levenshtein [11, 12]. Also we investigate the possibilities for attaining the Levenshtein bounds [11, 12]. In such cases...

Nonassociative triples in involutory loops and in loops of small order

Aleš Drápal, Jan Hora (2020)

Commentationes Mathematicae Universitatis Carolinae

A loop of order n possesses at least 3 n 2 - 3 n + 1 associative triples. However, no loop of order n > 1 that achieves this bound seems to be known. If the loop is involutory, then it possesses at least 3 n 2 - 2 n associative triples. Involutory loops with 3 n 2 - 2 n associative triples can be obtained by prolongation of certain maximally nonassociative quasigroups whenever n - 1 is a prime greater than or equal to 13 or n - 1 = p 2 k , p an odd prime. For orders n ≤ 9 the minimum number of associative triples is reported for both general and involutory...

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