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Characterisations of strong -matroids
Kieran Calvert, Aram Dermenjian, Alex Fink +1
We study characterisations of strong -matroids, compiling a list of five equivalent descriptions. We show a variant of Wenzel's exchange property and the hyperplane exchange pro…
Quadratic exchange equations for Coxeter matroids
Kieran Calvert, Aram Dermenjian, Alex Fink +1
Tropicalisation (with trivial coefficients) is a process that turns a polynomial equation into a combinatorial predicate on subsets of the set of variables. We show that for each m…
The polytope of all matroids
Luis Ferroni, Alex Fink
It is possible to write the indicator function of any matroid polytope as an integer combination of indicator functions of Schubert matroid polytopes. In this way, every matroid on…
The external activity complex of a pair of matroids
Andrew Berget, Alex Fink
We introduce the Schubert variety of a pair of linear subspaces in and the external activity complex of a pair of not necessarily realizable matroids. Both of these…
The omega invariant of a matroid
Alex Fink, Kris Shaw, David E Speyer
The third author introduced the -polynomial of a matroid, a covaluative matroid statistic which is unchanged under series and parallel extension. The -polynomial of…