6 research outputs found

    Some gregarious cycle decompositions of complete equipartite graphs

    Get PDF
    A k-cycle decomposition of a multipartite graph G is said to be gregarious if each k-cycle in the decomposition intersects k distinct partite sets of G. In this paper we prove necessary and sufficient conditions for the existence of such a decomposition in the case where G is the complete equipartite graph, having n parts of size m, and either n equivalent to 0, 1 (mod k), or k is odd and m equivalent to 0 (mod k). As a consequence, we prove necessary and sufficient conditions for decomposing complete equipartite graphs into gregarious cycles of prime length

    Multipartite graph decomposition: cycles and closed trails

    Get PDF
    This paper surveys results on cycle decompositions of complete multipartite graphs (where the parts are not all of size 1, so the graph is not K_n ), in the case that the cycle lengths are “small”. Cycles up to length n are considered, when the complete multipartite graph has n parts, but not hamilton cycles. Properties which the decompositions may have, such as being gregarious, are also mentioned

    Multipartite graph decomposition: cycles and closed trails

    Get PDF
    This paper surveys results on cycle decompositions of complete multipartite graphs (where the parts are not all of size 1, so the graph is not <em>K</em>_<em>n</em> ), in the case that the cycle lengths are “small”. Cycles up to length <em>n</em> are considered, when the complete multipartite graph has <em>n</em> parts, but not hamilton cycles. Properties which the decompositions may have, such as being gregarious, are also mentioned.<br /

    Two Problems of Gerhard Ringel

    Get PDF
    Gerhard Ringel was an Austrian Mathematician, and is regarded as one of the most influential graph theorists of the twentieth century. This work deals with two problems that arose from Ringel\u27s research: the Hamilton-Waterloo Problem, and the problem of R-Sequences. The Hamilton-Waterloo Problem (HWP) in the case of Cm-factors and Cn-factors asks whether Kv, where v is odd (or Kv-F, where F is a 1-factor and v is even), can be decomposed into r copies of a 2-factor made entirely of m-cycles and s copies of a 2-factor made entirely of n-cycles. Chapter 1 gives some general constructions for such decompositions and apply them to the case where m=3 and n=3x. This problem is settle for odd v, except for a finite number of x values. When v is even, significant progress is made on the problem, although open cases are left. In particular, the difficult case of v even and s=1 is left open for many situations. Chapter 2 generalizes the Hamilton-Waterloo Problem to complete equipartite graphs K(n:m) and shows that K(xyzw:m) can be decomposed into s copies of a 2-factor consisting of cycles of length xzm and r copies of a 2-factor consisting of cycles of length yzm, whenever m is odd, s,r≠1, gcd(x,z)=gcd(y,z)=1 and xyz≠0 (mod 4). Some more general constructions are given for the case when the cycles in a given two factor may have different lengths. These constructions are used to find solutions to the Hamilton-Waterloo problem for complete graphs. Chapter 3 completes the proof of the Friedlander, Gordon and Miller Conjecture that every finite abelian group whose Sylow 2-subgroup either is trivial or both non-trivial and non-cyclic is R-sequenceable. This settles a question of Ringel for abelian groups

    Equipartite gregarious 6- and 8-cycle systems

    No full text
    A k-cycle decomposition of a complete multipartite graph is said to be gregarious if each k-cycle in the decomposition has its vertices in k different partite sets. Equipartite gregarious 3-cycle systems are 3-GDDs, and necessary and sufficient conditions for their existence are known (see for instance the CRC Handbook of Combinatorial Designs, 1996, C. J. Colbourn, J. H. Dinitz (Eds.), Section III 1.3). The cases of equipartite and of almost equipartite 4-cycle systems were recently dealt with by Billington and Hoffman. Here, for both 6-cycles and for 8-cycles, we give necessary and sufficient conditions for existence of a gregarious cycle decomposition of the complete equipartite graph K-n(a) (with n parts, n >= 6 or n >= 8, of size a). (C) 2006 Elsevier B.V. All rights reserved

    Equipartite and almost-equipartite gregarious 4-cycle systems

    Get PDF
    A 4-cycle decomposition of a complete multipartite graph is said to be gregarious if each 4-cycle in the decomposition has its vertices in four different partite sets. Here we exhibit gregarious 4-cycle decompositions of the complete equipartite graph K (with n ≥ 4 parts of size m) whenever a 4-cycle decomposition (gregarious or not) is possible, and also of a complete multipartite graph in which all parts but one have the same size. The latter complete multipartite graph, K , having n parts of size m and one part of size t, has a gregarious 4-cycle decomposition if and only if (i) n ≥ 3, (ii) t ≤ ⌊ m (n - 1) / 2 ⌋ and (iii) a 4-cycle decomposition exists, that is, either m and t are even or else m and t are both odd and n ≡ 0 (mod 8)
    corecore