The cluster-algebra tropical fan conjecture

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Let A\mathcal{A} be a cluster algebra of finite type over R\mathbb{R}, let CC be its coefficient-variable set, and let S(A)S(\mathcal{A}) be its associated cluster complex. Consider the positive tropical variety Trop⁡+Spec⁡A\operatorname{Trop}^+ \operatorname{Spec} \mathcal{A} and its lineality space.

Tropical fan conjecture. If the lineality space of Trop⁡+Spec⁡A\operatorname{Trop}^+ \operatorname{Spec} \mathcal{A} has dimension ∣C∣|C|, then the quotient of Trop⁡+Spec⁡A\operatorname{Trop}^+ \operatorname{Spec} \mathcal{A} by its lineality space is a simplicial fan abstractly isomorphic to the cone over S(A)S(\mathcal{A}). If this dimension condition does not hold, the resulting fan is a coarsening of the cone over S(A)S(\mathcal{A}).

This conjecture proposes that using enough coefficient variables recovers the full cluster complex from the positive tropical variety, while insufficient coefficients produce a coarsening. The statement is motivated by the finite-type Grassmannian examples and by the observed failure for the coefficient-specialized cluster algebra of Gr2,6Gr_{2,6}; its general status is not established in the supplied source.

References

Primary source

David Speyer and Lauren K. Williams, “The tropical totally positive Grassmannian”, arXiv:math/0312297 (2003).

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