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Updated: May 15, 2025

Scattering And Absorption of Light in Planetary Regoliths
Published on: July 1, 2019
Scattering diagrams, tight gradings, and generalized positivity
Amanda Burcroff1, Kyungyong Lee2,3, Lang Mou4
1Department of Mathematics, Harvard University, Cambridge, MA 02138.
None:
In 2013, Lee, Li, and Zelevinsky introduced combinatorial objects called compatible pairs to construct the greedy bases for rank-2 cluster algebras, consisting of indecomposable positive elements including the cluster monomials. Subsequently, Rupel extended this construction to the setting of generalized rank-2 cluster algebras by defining compatible gradings. We find a class of combinatorial objects which we call tight gradings. Using this, we give a directly computable, manifestly positive, and elementary but highly nontrivial formula describing rank-2 consistent scattering diagrams. This allows us to show that the coefficients of the wall-functions on a generalized cluster scattering diagram of any rank are positive, which implies the Laurent positivity for generalized cluster algebras and the strong positivity of their theta bases.
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