ECCC-Report TR15-125https://eccc.weizmann.ac.il/report/2015/125Comments and Revisions published for TR15-125en-usSun, 11 Jun 2017 23:46:29 +0300
Revision 2
| Improved Constructions of Two-Source Extractors |
Xin Li
https://eccc.weizmann.ac.il/report/2015/125#revision2In a recent breakthrough \cite{CZ15}, Chattopadhyay and Zuckerman gave an explicit two-source extractor for min-entropy $k \geq \log^C n$ for some large enough constant $C$, where $n$ is the length of the source. However, their extractor only outputs one bit. In this paper, we improve the output of the two-source extractor to $k^{\Omega(1)}$, while the error remains $n^{-\Omega(1)}$ and the extractor remains strong in the second source. In the non-strong case, the output can be increased to $k$. Our improvement is obtained by giving a better extractor for $(q, t, \gamma)$ non-oblivious bit-fixing sources, which can output $t^{\Omega(1)}$ bits instead of one bit as in \cite{CZ15}.
We also give the first explicit construction of deterministic extractors for affine sources over $F_2$, with entropy $k \geq \log^C n$ for some large enough constant $C$, where $n$ is the length of the source. Previously the best known results are by Bourgain \cite{Bourgain07}, Yehudayoff \cite{Yehudayoff10} and Li \cite{Li11a}, which require the affine source to have entropy at least $\Omega(n/\sqrt{\log \log n})$. Our extractor outputs $k^{\Omega(1)}$ bits with error $n^{-\Omega(1)}$. This is done by reducing an affine source to a non-oblivious bit-fixing source, where we adapt the alternating extraction based approach in previous work on independent source extractors \cite{Li13b} to the affine setting. Our affine extractors also imply improved extractors for circuit sources studied in \cite{Viola11}.
We further extend our results to the case of zero-error dispersers, and give two applications in data structures that rely crucially on the fact that our two-source or affine extractors have large output size.Sun, 11 Jun 2017 23:46:29 +0300https://eccc.weizmann.ac.il/report/2015/125#revision2
Revision 1
| Improved Two-Source Extractors, and Affine Extractors for Polylogarithmic Entropy |
Xin Li
https://eccc.weizmann.ac.il/report/2015/125#revision1In a recent breakthrough \cite{CZ15}, Chattopadhyay and Zuckerman gave an explicit two-source extractor for min-entropy $k \geq \log^C n$ for some large enough constant $C$, where $n$ is the length of the source. However, their extractor only outputs one bit. In this paper, we improve the output of the two-source extractor to $k^{\Omega(1)}$, while the error remains $n^{-\Omega(1)}$ and the extractor remains strong in the second source. In the non-strong case, the output can be increased to $k$.\ Our improvement is obtained by giving a better extractor for $(q, t, \gamma)$ non-oblivious bit-fixing sources, which can output $t^{\Omega(1)}$ bits instead of one bit as in \cite{CZ15}.
We also give the first explicit construction of deterministic extractors for affine sources over $\F_2$, with entropy $k \geq \log^C n$ for some large enough constant $C$, where $n$ is the length of the source. Previously the best known results are by Bourgain \cite{Bourgain07}, Yehudayoff \cite{Yehudayoff10} and Li \cite{Li11a}, which require the affine source to have entropy at least $\Omega(n/\sqrt{\log \log n})$. Our extractor outputs $k^{\Omega(1)}$ bits with error $n^{-\Omega(1)}$. This is done by reducing an affine source to a non-oblivious bit-fixing source, where we adapt the alternating extraction based approach in previous work on independent source extractors \cite{Li13b} to the affine setting. Our affine extractors also imply improved extractors for circuit sources studied in \cite{Viola11}.Wed, 03 Feb 2016 00:30:26 +0200https://eccc.weizmann.ac.il/report/2015/125#revision1
Paper TR15-125
| Improved Constructions of Two-Source Extractors |
Xin Li
https://eccc.weizmann.ac.il/report/2015/125In a recent breakthrough \cite{CZ15}, Chattopadhyay and Zuckerman gave an explicit two-source extractor for min-entropy $k \geq \log^C n$ for some large enough constant $C$. However, their extractor only outputs one bit. In this paper, we improve the output of the two-source extractor to $k^{\Omega(1)}$, while the error remains $n^{-\Omega(1)}$.
Our improvement is obtained by giving a better extractor for $(q, t, \gamma)$ non-oblivious bit-fixing sources, which can output $t^{\Omega(1)}$ bits instead of one bit as in \cite{CZ15}.
Thu, 06 Aug 2015 14:08:47 +0300https://eccc.weizmann.ac.il/report/2015/125