Braid-arrangement minimizer conjecture for matroid fans

Let MM be a loopless matroid on a finite ground set EE, and let 4Σ(M)RE4\Sigma(M) \subseteq \mathbb{R}^E be its matroid fan. For a rational subspace RRER \subseteq \mathbb{R}^E, define

adim(M):=min{2dimR(Σ(M)+R)dimR(R)RRE is rational}.\operatorname{adim}(M):=\min\{2\dim_{\mathbb{R}}(\Sigma(M)+R)-\dim_{\mathbb{R}}(R)\mid R\subseteq\mathbb{R}^E\text{ is rational}\}.

Here a rational subspace is spanned by its intersection with QE\mathbb{Q}^E, and Σ(M)+R\Sigma(M)+R denotes the Minkowski sum. Braid-arrangement minimizer conjecture. The minimum is attained by some subspace RR in the braid arrangement, namely an intersection of hyperplanes of the form xi=xjx_i=x_j for distinct i,jEi,j\in E.

This conjecture would make the matroidal formula for amoeba dimension more explicit by restricting the minimization to braid-arrangement subspaces. The paper presents its theorem as being inspired by this conjecture; no resolution is supplied in the given text.

Sources & referencesView supporting material

Primary source

Jan Draisma, Sarah Eggleston, Rudi Pendavingh, Johannes Rau and Chi Ho Yuen, “The amoeba dimension of a linear space”, arXiv:2303.13143 (2023).

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