Extremal bipartite independence number and balanced coloring

Abstract

In this paper, we establish a couple of results on extremal problems in bipartite graphs. Firstly, we show that every sufficiently large bipartite graph with average degree $D$ and with $n$ vertices on each side has a balanced independent set containing $(1-\epsilon )\frac{\log D}{D}n$ vertices from each side for small $\epsilon >0$. Secondly, we prove that the vertex set of every sufficiently large balanced bipartite graph with maximum degree at most $\Delta$ can be partitioned into $(1+\epsilon )\frac{\Delta }{\log \Delta }$ balanced independent sets. Both of these results are algorithmic and best possible up to a factor of 2, which might be hard to improve as evidenced by the phenomenon known as `algorithmic barrier' in the literature. The first result improves a recent theorem of Axenovich, Sereni, Snyder, and Weber in a slightly more general setting. The second result improves a theorem of Feige and Kogan about coloring balanced bipartite graphs.

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• Probabilistic Tools for the Analysis of Randomized Optimization Heuristics