diff --git a/main.tex b/main.tex index 63b7660..a780b82 100644 --- a/main.tex +++ b/main.tex @@ -356,11 +356,16 @@ for each 2-approx mincut $C$ in $(G,w_\lambda)$:\\ return the optimal $(C,F)$ \end{algo} -\paragraph{time for $\lambda^*$} $L(\lambda)-b\lambda$ is pwl concave. The number of segments is at most $3^m$. We need almost linear time to find the solution to a fixed $\lambda$. So parametric seach gives complexity $m^{1+o(1)} O(\log 3^m)$. -\note{need to check this} +To compute $\lambda^*$ we need to use parametric search. +\begin{lemma}[\cite{salowe_parametric}] +Let $S(n)$ be the complexity of solving the Lagrangian dual problem for fixed $\lambda$ (where $n$ is the size of the input), then one can compute $\lambda^*$ using parametric search in $O(S(n)^2)$ time. +\end{lemma} +It follows directly from the preceding lemma that $\lambda^*$ can be computed in $\tilde O(m^2)$ time. -\paragraph{time for the rest parts} Reweighting takes linear time. -Finding $<2$-approx mincut takes $\tilde O(n^3)$. FPTAS for knapsack takes $O(\frac{1}{\e}m^2)$. The total complexity is $O(\frac{1}{\e}m^2n^3)$. +Reweighting the graph takes linear time. +Finding $<2$-approx mincut takes $\tilde O(n^3)$. +An $1+\e$ approximate solution to knapsack can be found in time $\tilde O(m+\frac{1}{\e^2})$ \cite{10.1145/3618260.3649730}. +The total complexity is $\tilde O(mn^3+\frac{n^3}{\e^2})$. \bibliographystyle{plain} \bibliography{ref} diff --git a/ref.bib b/ref.bib index 7e8398b..fcd88a2 100644 --- a/ref.bib +++ b/ref.bib @@ -81,5 +81,33 @@ abstract = { This paper considers the problem of designing fast, approximate, co pages = {1334--1353}, } +@inproceedings{10.1145/3618260.3649730, +author = {Chen, Lin and Lian, Jiayi and Mao, Yuchen and Zhang, Guochuan}, +title = {A Nearly Quadratic-Time FPTAS for Knapsack}, +year = {2024}, +isbn = {9798400703836}, +publisher = {Association for Computing Machinery}, +address = {New York, NY, USA}, +url = {https://doi.org/10.1145/3618260.3649730}, +doi = {10.1145/3618260.3649730}, +abstract = {We investigate the classic Knapsack problem and propose a fully polynomial-time approximation scheme (FPTAS) that runs in O(n + (1/)2) time. Prior to our work, the best running time is O(n + (1/)11/5) [Deng, Jin, and Mao’23]. Our algorithm is the best possible (up to a polylogarithmic factor), as Knapsack has no O((n + 1/)2−δ)-time FPTAS for any constant δ > 0, conditioned on the conjecture that (min, +)-convolution has no truly subquadratic-time algorithm.}, +booktitle = {Proceedings of the 56th Annual ACM Symposium on Theory of Computing}, +pages = {283–294}, +numpages = {12}, +keywords = {Approximation scheme, Knapsack}, +location = {Vancouver, BC, Canada}, +series = {STOC 2024} +} +@inbook{salowe_parametric, +author = {Salowe, Jeffrey S.}, +title = {Parametric search}, +year = {1997}, +isbn = {0849385245}, +publisher = {CRC Press, Inc.}, +address = {USA}, +booktitle = {Handbook of Discrete and Computational Geometry}, +pages = {683–695}, +numpages = {13} +} \ No newline at end of file