P = latticePoints(FM)
For a basis $B= \{B_1, \ldots, B_k\}$ of a flag matroid $M$ (see bases(FlagMatroid)), let $e_B$ be the sum over $i = 1, \ldots, k$ of the indicator vectors of $B_i$. The base polytope of a flag matroid $M$ is the convex hull of $e_B$ as $B$ ranges over all bases of $M$. This method computes the lattice points of the base polytope of a flag matroid, exploiting the strong normality property as proven in [CDMS18].
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In terms of equivariant K-theory, the lattice points of the base polytope of a flag matroid is equal to the integer-point transform of the equivariant Euler characteristic (see euler(KClass)) of the KClass defined by the flag matroid shifted by the $O(1)$ bundle on the (partial) flag variety.
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