Weight-Two Classification for positive tropical Grassmannians

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Let I,J∈([n]k)ncycI,J\in {\binom{[n]}{k}}^{\mathrm{ncyc}} be noncrossing but not weakly separated. For each such II, let tI\mathfrak{t}_I denote the corresponding noncrossing parameter, and let ρ\rho be the positive parameterization into the positive tropical Grassmannian.

Weight-Two Classification. The point

ρ(tI+tJ)\rho(\mathfrak{t}_I+\mathfrak{t}_J)

lies in the direction of a ray of Trop⁡>0X(k,n)\operatorname{Trop}_{>0}X(k,n). Every ray of Trop⁡>0X(k,n)\operatorname{Trop}_{>0}X(k,n) with PK weight 22 arises in this way from a unique noncrossing but not weakly separated pair I,J\\{I,J\\}.

This conjecture gives the proposed classification of the weight-two rays of the positive tropical Grassmannian, extending the preceding classification of weight-one rays. It was stated previously in the cited work, but its resolution is not specified in the supplied context.

References

Primary source

Nick Early and Thomas Lam, “Noncrossing Duality and the Geometry of Positive Tropical Linear Spaces”, arXiv:2604.25212 (2026).

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