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Donggyu Kim (๊น€๋™๊ทœ), ๐˜-graphic delta-matroids and their applications

Tuesday, October 26, 2021 @ 4:30 PM - 5:30 PM KST

Room B232, IBS (๊ธฐ์ดˆ๊ณผํ•™์—ฐ๊ตฌ์›)

Bouchet (1987) defined delta-matroids by relaxing the base exchange axiom of matroids. Oum (2009) introduced a graphic delta-matroid from a pair of a graph and its vertex subset. We define a $\Gamma$-graphic delta-matroid for an abelian group $\Gamma$, which generalizes a graphic delta-matroid.

For an abelian group $\Gamma$, a $\Gamma$-labelled graph is a graph whose vertices are labelled by elements of $\Gamma$. We prove that a certain collection of edge sets of a $\Gamma$-labelled graph forms a delta-matroid, which we call a $\Gamma$-graphic delta-matroid, and provide a polynomial-time algorithm to solve the separation problem, which allows us to apply the symmetric greedy algorithm of Bouchet (1987) to find a maximum weight feasible set in such a delta-matroid. We also prove that a $\Gamma$-graphic delta-matroid is a graphic delta-matroid if and only if it is even. We prove that every $\mathbb{Z}_p^k$-graphic delta matroid is represented by some symmetric matrix over a field of characteristic of order $p^k$, and if every $\Gamma$-graphic delta-matroid is representable over a finite field $\mathbb{F}$, then $\Gamma$ is isomorphic to $\mathbb{Z}_p^k$ and $\mathbb{F}$ is a field of order $p^\ell$ for some prime $p$ and positive integers $k$ and $\ell$.

This is joint work with Duksang Lee and Sang-il Oum.


Tuesday, October 26, 2021
4:30 PM - 5:30 PM KST
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Room B232
IBS (๊ธฐ์ดˆ๊ณผํ•™์—ฐ๊ตฌ์›)


Sang-il Oum (์—„์ƒ์ผ)
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