Low Degree Nullstellensatz Certificates for 3-Colorability

Abstract. In a seminal paper, De Loera et. al introduce the algorithm NulLA (Nullstellensatz Linear Algebra) and use it to measure the difficulty of determining if a graph is not 3-colorable. The crux of this relies on a correspondence between 3-colorings of a graph and solutions to a certain system of polynomial equations over a field k. In this article, we give a new direct combinatorial characterization of graphs that can be determined to be non-3colorable in the first iteration of this algorithm when k = GF(2). This greatly simplifies the work of De Loera et. al, as we express the combinatorial characterization directly in terms of the graphs themselves without introducing superfluous directed graphs. Furthermore, for all graphs on at most 12 vertices, we determine at which iteration NulLA detects a graph is not 3-colorable when k = GF(2).

• Type: Journal
• Year: 2016
• Where: COMBINATORICS
• Authors: Bo Li, Benjamin Lowenstein, Mohamed Omar
• Keywords: COMBINATORICS 2016