gap 4 conj doesn't seem correct... fixed some setminus

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Yu Cong 2025-05-05 22:46:29 +08:00
parent 6e0a354fe9
commit 0d883a033e

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@ -121,7 +121,7 @@ s.t.& & \sum_{e\in T} x_e+y_e&\geq 1 & &\forall T & &\text{($x+y$ is
\begin{frame}{Normalized Mincut from LP}
One standard trick for dealing LPs with knapsack constraints is to consider its Lagrangian dual.
\begin{equation*}
\max_{\mu\geq 0} L(\mu)= \max_{\mu\geq 0} \min \left\{ w(C-F)-\mu(b-c(F)) | \forall \text{cut $C$}\;\forall F\subset C
\max_{\mu\geq 0} L(\mu)= \max_{\mu\geq 0} \min \left\{ w(C\setminus F)-\mu(b-c(F)) | \forall \text{cut $C$}\;\forall F\subset C
% \land c(F)\leq b
\right\}
\end{equation*}
@ -130,11 +130,11 @@ One standard trick for dealing LPs with knapsack constraints is to consider its
$L(\mu)$ is piecewise linear and concave.
\end{lemma}
For fixed $\mu$, how to solve $\min\limits_{C,F} \left\{ w(C-F)-\mu(b-c(F))
For fixed $\mu$, how to solve $\min\limits_{C,F} \left\{ w(C\setminus F)-\mu(b-c(F))
\right\}$?
For small enough $\mu\geq 0$, $w(C-F)$ term is dominanting.
Thus the optimal solution must be $C=F=\text{mincut with weight $c$}$.
For small enough $\mu\geq 0$, $w(C\setminus F)$ term is dominanting.
Thus the optimal solution must be $C=F=\text{mincut with capacity $c$}$.
\end{frame}
@ -144,7 +144,7 @@ We have see that the first line segment is $L(\mu)=(\lambda_c-b)\mu$ where $\lam
What is the first breakpoint on $L(\mu)$?
\newline
We have $-\mu(b-\lambda_c)\leq w(C- F)-\mu(b-c(F))$ for any cut $C$ and $F\subsetneq C$. Thus the first breakpoint is $\mu=\min \frac{w(C- F)}{\lambda_c-c(F)}$, which is the value of normalized mincut.
We have $-\mu(b-\lambda_c)\leq w(C\setminus F)-\mu(b-c(F))$ for any cut $C$ and $F\subsetneq C$. Thus the first breakpoint is $\mu=\min \frac{w(C\setminus F)}{\lambda_c-c(F)}$, which is the value of normalized mincut.
\newline
What about other breakpoints?
@ -173,19 +173,19 @@ Again we first assume the $\mu$ is fixed. Then for each pair of constraints $\su
\end{frame}
\begin{frame}{Integrality Gap}
\begin{conjecture}
ILP\ref{IP} has an integrality gap of 4.
\end{conjecture}
% \begin{conjecture}
% ILP\ref{IP} has an integrality gap of 4.
% \end{conjecture}
Suppose $\mu^*$ is the optimal solution to LP\ref{lp:dualcutint}. Let $\lambda^{fr}$ be the fractional mincut with capacity $w_\mu$.
% Suppose $\mu^*$ is the optimal solution to LP\ref{lp:dualcutint}. Let $\lambda^{fr}$ be the fractional mincut with capacity $w_\mu$.
we have
\begin{align*}
4\opt(LP) &=4\lambda^{fr}-4b\mu^*\\
&\geq 2\lambda^{int} - 4b\mu^*\\
&\geq w_{\mu^*}(C^*)-b\mu^*,
\end{align*}
which implies Theorem \autoref{thm:2approx}.
% we have
% \begin{align*}
% 4\opt(LP) &=4\lambda^{fr}-4b\mu^*\\
% &\geq 2\lambda^{int} - 4b\mu^*\\
% &\geq w_{\mu^*}(C^*)-b\mu^*,
% \end{align*}
% which implies Theorem \autoref{thm:2approx}.
\end{frame}
\begin{frame}{References}
\bibliographystyle{plainnat}