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\maketitle
\section{Connectivity interdiction}
\begin{frame}{Connectivity interdiction}
\begin{problem}[connectivity interdiction {[Zenklusen ORL'14]}]
\begin{problem}[connectivity interdiction {[Zenklusen, ORL'14]}]
Let $G=(V,E)$ be a graph with edge weights $w:E\to\Z_+$ and edge removal costs $c:E\to\Z_+$ and let $B\in \mathbb Z_+$ be the budget.
Find $F\subset E$ with $w(F)\leq B$ s.t. the min-cut in $G-F$ is minimized.
@@ -74,10 +74,10 @@ Find the cut with minimum weight $w'$.
\toprule
unit cost $w(\cdot)=1$ & general case & random? & ref \\
\midrule
$O(m^2n^4\log n)$ & $O(m^{2+1/\e}n^4\log n)$ & $\times$ & [Zenklusen ORL'14] \\
$O(mn^4\log^2 n)$ & $O(m^{1+1/\e}n^4\log^2 n)$ & $\checkmark$ & [Zenklusen ORL'14] \\
$\tilde O(m+n^4 B)$ & $O(\frac{m^2n^4}{\e}\log(Bnw_{\max}))$ & $\times$ & [Huang \etal{} IPCO'24]\\
$\tilde O(mn^3\log w_{\max})$ & - & $\checkmark$ & [Drange \etal{} AAAI'26]\\
$O(m^2n^4\log n)$ & $O(m^{2+1/\e}n^4\log n)$ & $\times$ & [Zenklusen, ORL'14] \\
$O(mn^4\log^2 n)$ & $O(m^{1+1/\e}n^4\log^2 n)$ & $\checkmark$ & [Zenklusen, ORL'14] \\
$\tilde O(m+n^4 B)$ & $O(\frac{m^2n^4}{\e}\log(Bnw_{\max}))$ & $\times$ & [Huang \etal{}, IPCO'24]\\
$\tilde O(mn^3\log w_{\max})$ & - & $\checkmark$ & [Drange \etal{}, AAAI'26]\\
$\tilde O(m^2+n^3B)$ & $\tilde O(m^2+mn^3+n^3/\e)$ & $\times$ & this work\\
$\tilde O(m+n^3B)$ & $\tilde O(mn^3+n^3/\e)$ & $\checkmark$ & this work\\
\bottomrule
@@ -86,18 +86,18 @@ $\tilde O(m+n^3B)$ & $\tilde O(mn^3+n^3/\e)$ & $\checkmark$ & this work\\
\end{table}
\end{frame}
\begin{frame}{Method in [Huang \etal{} IPCO'24]}
\begin{frame}{Method in [Huang \etal{}, IPCO'24]}
\begin{problem}[\emph{normalized min-cut} {[Chalermsook \etal{} ICALP'22]}]
\begin{problem}[\emph{normalized min-cut} {[Chalermsook \etal{}, ICALP'22]}]
Given the same input as connectivity interdiction, find
\[\argmin_{\text{cut $C$}, F\subset C} \frac{w(C-F)}{B-c(F)+1} \quad s.t. \quad 0\leq c(F)\leq B.\]
\end{problem}
\p
First considered in [Chalermsook \etal{} ICALP'22] as a subproblem in MWU framework when solving minimum $k$-edge connected spanning subgraph (ECSS) problem.
First considered in [Chalermsook \etal{}, ICALP'22] as a subproblem in MWU framework when solving minimum $k$-edge connected spanning subgraph (ECSS) problem.
\end{frame}
\begin{frame}{Method in [Huang \etal{} IPCO'24]}
\begin{frame}{Method in [Huang \etal{}, IPCO'24]}
Let $\tau$ be a $(1+\e)$-approximation to the normalized min-cut and let $C^*$ be the optimal $B$-free cut.
\begin{lemma}
$C^*$ is a $(2+2\e)$-approximate min-cut in $(G,w_\tau)$,
@@ -171,18 +171,18 @@ P & & P & & P & & \textcolor{BrickRed}{\text{NP-Hard}}
\]
\p
\begin{conjecture}[{[Geelen \etal{} Ann. Comb. 2015]}]
\begin{conjecture}[{[Geelen \etal{}, Ann. Comb. 2015]}]
For any proper minor-closed class $\mathcal M$ of binary matroids, there is a polynomial time algorithm for computing the girth of matroids in $\mathcal M$.
\end{conjecture}
\end{frame}
\begin{frame}{Perturbed graphic matroid}
\begin{theorem}[{[Geelen \etal{} Ann. Comb. 2015]}]
\begin{theorem}[{[Geelen \etal{}, Ann. Comb. 2015]}]
For any proper minor-closed class $\mathcal M$ of binary matroids, there exists two constants $k,t\in \Z_+$ such that, for each vertically $k$-connected matroid $M\in \mathcal M$, there exist matrices $A,P\in \F_2^{r\times n}$ such that $A$ is the incidence matrix of a graph, $\mathrm{rank}(P)\leq t$, and either $M$ or $M^*$ is isomorphic to $M(A+P)$.
\end{theorem}
\p
\begin{theorem}[{[Geelen \& Kapadia Combinatorica'17]}]
\begin{theorem}[{[Geelen \& Kapadia, Combinatorica'17]}]
There are polynomial-time randomized algorithms for computing the girth and the cogirth of $M(A+P)$.
\end{theorem}
@@ -215,13 +215,13 @@ $M(A)$ is a \emph{$(1,t)$-signed graft}.
\begin{frame}{Previous works}
Results on computing the cogirth of $(1,t)$-signed grafts:
\begin{itemize}
\item $O(r^5n)$ random algorithm [Geelen \& Kapadia Combinatorica'17]
\item $n^{O(1)}$ deterministic algorithm when the $\set{s}$-indexed row is all 0 [Nägele \etal{} SODA'18]
\item $O(r^5n)$ random algorithm [Geelen \& Kapadia, Combinatorica'17]
\item $n^{O(1)}$ deterministic algorithm when the $\set{s}$-indexed row is all 0 [Nägele \etal{}, SODA'18]
\end{itemize}
\end{frame}
\begin{frame}{Method}
\begin{theorem}[{[Chekuri \etal{} SOSA'19]}]
\begin{theorem}[{[Chekuri \etal{}, SOSA'19]}]
Given a matroid $M$, let $\lambda(M)$ be its cogirth and let $\sigma(M)$ be the fractional base packing number.
If there is some constant $c$ that $\frac{\lambda(M)}{\sigma(M)}<c$, then the cogirth of $M$ can be computed deterministically in polynomial number of calls to the independence oracle.
\end{theorem}