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Mikhail Gudim

Publications and source records attributed to Mikhail Gudim.

3 recordsLinked to original sources

Ordered Dags: HypercubeSort

We generalise the insertion into a binary heap to any directed acyclic graph (DAG) with one source vertex. This lets us formulate a general method for converting any such DAG into a data structure with priority queue interface. We apply our method to a hypercube DAG to obtain a sorting algorithm of complexity $\mathcal{O}(n\log^2 (n))$. As another curious application, we derive a relationship between length of longest path and maximum degree of a vertex in a DAG.

cs.DS

On Cohomology of Complexes Associated with a Generic Matrix

In the appendix of the famous book "Commutative Algebra with a View Towards Algebraic Geometry" one can find an infinite family of complexes indexed by integers. This family includes Eagon-Northcott and Buschsbaum-Rim complexes. The objective of this paper is to study this family, and, in particular, refine the knowledge of its cohomology. First, we obtain these complexes from the derived images of twists of the Koszul complex on the projective space. This idea apparently goes back to Kempf [1970]. Taking this "geometric" point of view, we interpret the cohomology of these complexes as the cohomology of certain vector bundles on the projective space, and proceed with calculations. Finally, we put the above results in the realm of tilting theory: non-exactness of this family in certain regions can be seen as a failure of the exceptional sequence of line bundles on the projective space to lift to an exceptional sequence on a certain vector bundle. This observation creates a curious contrast with the results of Buchweitz-Leushke-Van den Bergh, stating that the exceptional sequence of twisted differential forms does lift to an exceptional sequence on the same vector bundle.

math.AC

Elementary Equivariant Modules

We study equivariant modules over $GL(V)$ over the polynomial ring $R = Sym V$. We introduce for every partition $λ$ the elementary equivariant module $M_λ$. Then we prove that any finitely generated equivariant module admits a fltration with associated graded being the direct sum of modules of only two kinds: either $M_λ$ or truncations of $M_λ$. We show that each $M_λ$ has a linear resolution and describe also the resolution of its truncations.

math.AC