Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA blow-up lemma for approximate decompositions
183
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We develop a new method for constructing approximate decompositions of dense graphs into sparse graphs and apply it to longstanding decomposition problems. For instance, our results imply the following. Let $G$ be a quasi-random $n$-vertex graph and suppose $H_1,dots,H_s$ are bounded degree $n$-vertex graphs with $sum_{i=1}^{s} e(H_i) leq (1-o(1)) e(G)$. Then $H_1,dots,H_s$ can be packed edge-disjointly into $G$. The case when $G$ is the complete graph $K_n$ implies an approximate version of the tree packing conjecture of Gyarfas and Lehel for bounded degree trees, and of the Oberwolfach problem. We provide a more general version of the above approximate decomposition result which can be applied to super-regular graphs and thus can be combined with Szemeredis regularity lemma. In particular our result can be viewed as an extension of the classical blow-up lemma of Komlos, SarkH{o}zy and Szemeredi to the setting of approximate decompositions.
rate research
Read More
Kim, Kuhn, Osthus and Tyomkyn (Trans. Amer. Math. Soc. 371 (2019), 4655--4742) greatly extended the well-known blow-up lemma of Komlos, Sarkozy and Szemeredi by proving a `blow-up lemma for approximate decompositions which states that multipartite quasirandom graphs can be almost decomposed into any collection of bounded degree graphs with the same multipartite structure and slightly fewer edges. This result has already been used by Joos, Kim, Kuhn and Osthus to prove the tree packing conjecture due to Gyarfas and Lehel from 1976 and Ringels conjecture from 1963 for bounded degree trees as well as implicitly in the recent resolution of the Oberwolfach problem (asked by Ringel in 1967) by Glock, Joos, Kim, Kuhn and Osthus. Here we present a new and significantly shorter proof of the blow-up lemma for approximate decompositions. In fact, we prove a more general theorem that yields packings with stronger quasirandom properties so that it can be combined with Keevashs results on designs to obtain results of the following form. For all $varepsilon>0$, $rin mathbb{N}$ and all large $n$ (such that $r$ divides $n-1$), there is a decomposition of $K_n$ into any collection of $r$-regular graphs $H_1,ldots,H_{(n-1)/r}$ on $n$ vertices provided that $H_1,ldots,H_{varepsilon n}$ contain each at least $varepsilon n$ vertices in components of size at most $varepsilon^{-1}$.
A subgraph of an edge-coloured graph is called rainbow if all its edges have different colours. We prove a rainbow version of the blow-up lemma of Komlos, Sarkozy and Szemeredi that applies to almost optimally bounded colourings. A corollary of this is that there exists a rainbow copy of any bounded-degree spanning subgraph $H$ in a quasirandom host graph $G$, assuming that the edge-colouring of $G$ fulfills a boundedness condition that is asymptotically best possible. This has many applications beyond rainbow colourings, for example to graph decompositions, orthogonal double covers and graph labellings.
The blow-up lemma states that a system of super-regular pairs contains all bounded degree spanning graphs as subgraphs that embed into a corresponding system of complete pairs. This lemma has far-reaching applications in extremal combinatorics. We prove sparse analogues of the blow-up lemma for subgraphs of random and of pseudorandom graphs. Our main results are the following three spar
We study lattice-theoretical extensions of the celebrated Sauer-Shelah-Perles Lemma. We conjecture that a general Sauer-Shelah-Perlem Lemma holds for a lattice $L$ if and only if $L$ is relatively complemented, and prove partial results towards this conjecture.
For a subgraph $G$ of the blow-up of a graph $F$, we let $delta^*(G)$ be the smallest minimum degree over all of the bipartite subgraphs of $G$ induced by pairs of parts that correspond to edges of $F$. In [Triangle-factors in a balanced blown-up triangle. Discrete Mathematics, 2000], Johansson proved that if $G$ is a spanning subgraph of the blow-up of $C_3$ with parts of size $n$ and $delta^*(G) ge frac{2}{3}n + sqrt{n}$, then $G$ contains $n$ vertex-disjoint triangles, and presented the following conjecture of Haggkvist: If $G$ is a spanning subgraph of the blow-up of $C_k$ with parts of size $n$ and $delta^*(G) ge (1 + 1/k)n/2 + 1$, then $G$ contains $n$ vertex disjoint copies of $C_k$ such that each $C_k$ intersects each of the $k$ parts exactly once. The degree condition of this conjecture is tight when $k=3$ and cannot be strengthened by more than one when $k ge 4$., A similar conjecture was also made by Fischer in [Variants of the Hajnal-Szemeredi Theorem. Journal of Graph Theory, 1999] and the triangle case was proved for large $n$ by Magyar and Martin in [Tripartite version of the Corradi-Hajnal Theorem. Discrete Mathematics, 2002]. In this paper, we prove this Conjecture asymptotically. We also pose a conjecture which generalizes this result by allowing the minimum degree conditions on the nonempty bipartite subgraphs induced by pairs of parts to vary. Our second result supports this new conjecture by proving the triangle case. This result generalizes Johannsons result asymptotically.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
