PBW filtration and bases for irreducible modules in type An

E Feigin, G Fourier, P Littelmann - Transformation Groups, 2011 - Springer
We study the PBW filtration on the highest weight representations V (λ) of sl _ n+ 1. This
filtration is induced by the standard degree filtration on U\left (n^-\right). We give a …

[LLIBRE][B] Combinatorial reciprocity theorems

M Beck, R Sanyal - 2018 - books.google.com
Combinatorial reciprocity is a very interesting phenomenon, which can be described as
follows: A polynomial, whose values at positive integers count combinatorial objects of some …

PBW filtration and bases for symplectic Lie algebras

E Feigin, G Fourier, P Littelmann - International Mathematics …, 2011 - ieeexplore.ieee.org
We study the PBW filtration on the highest weight representations V (λ) of sp_2n. This
filtration is induced by the standard degree filtration on U(n^-). We give a description of the …

On toric degenerations of flag varieties

X Fang, G Fourier, P Littelmann - Representation theory—current trends …, 2017 - ems.press
Following the historical track in pursuing T-equivariant flat toric degenerations of flag
varieties and spherical varieties, we explain how powerful tools in algebraic geometry and …

Favourable modules: filtrations, polytopes, Newton–Okounkov bodies and flat degenerations

E Feigin, G Fourier, P Littelmann - Transformation Groups, 2017 - Springer
We introduce the notion of a favourable module for a complex unipotent algebraic group,
whose properties are governed by the combinatorics of an associated polytope. We …

[HTML][HTML] Coupled cluster degree of the Grassmannian

V Borovik, B Sturmfels, S Sverrisdóttir - Journal of Symbolic Computation, 2025 - Elsevier
We determine the number of complex solutions to a nonlinear eigenvalue problem on the
Grassmannian in its Plücker embedding. This is motivated by quantum chemistry, where it …

[HTML][HTML] Marked chain-order polytopes

X Fang, G Fourier - European Journal of Combinatorics, 2016 - Elsevier
We introduce in this paper the marked chain-order polytopes associated to a marked poset,
generalizing the marked chain polytopes and marked order polytopes by putting them as …

Gelfand--Tsetlin Polytopes: A Story of Flow and Order Polytopes

RI Liu, K Mészáros, AS Dizier - SIAM Journal on Discrete Mathematics, 2019 - SIAM
Gelfand--Tsetlin polytopes are prominent objects in algebraic combinatorics. The number of
integer points of the Gelfand--Tsetlin polytope GT(λ) is equal to the dimension of the …

Relative poset polytopes and semitoric degenerations

E Feigin, I Makhlin - Selecta Mathematica, 2024 - Springer
The two best studied toric degenerations of the flag variety are those given by the Gelfand–
Tsetlin and FFLV polytopes. Each of them degenerates further into a particular monomial …

Birational Maps to Grassmannians, Representations and Poset Polytopes: An Appendix in Collaboration with Wojciech Samotij

E Feigin - Algebras and Representation Theory, 2024 - Springer
We study the closure of the graph of the birational map from a projective space to a
Grassmannian. We provide explicit description of the graph closure and compute the fibers …