TY - GEN

T1 - 2-Source dispersers for sub-polynomial entropy and ramsay graphs beating the frankl-wilson construction

AU - Barak, Boaz

AU - Rao, Anup

AU - Shaltiel, Ronen

AU - Wigderson, Avi

PY - 2006

Y1 - 2006

N2 - The main result of this paper is an explicit disperser for two independent sources on n bits, each of entropy k = no(1). Put differently, setting N = T and K = 2 n, we construct explicit N × N Boolean matrices for which no K × K submatrix is monochromatic. Viewed as adjacency matrices of bipartite graphs, this gives an explicit construction of K-Ramsey bipartite graphs of size N. This greatly improves the previous bound of k = o(n) of Barak, Kindler, Shaltiel, Sudakov and Wigderson [4]. It also significantly improves the 25-year record of k = Õ(√n) on the special case of Ramsey graphs, due to Frankl and Wilson [9]. The construction uses (besides "classical" extractor ideas) almost all of the machinery developed in the last couple of years for extraction from independent sources, including: Bourgain's extractor for 2 independent sources of some entropy rate < 1/2 [5] Raz's extractor for 2 independent sources, one of which has any entropy rate > 1/2 [18] Rao's extractor for 2 independent block-sources of entropy n Ω(1) [17] The "Challenge-Response" mechanism for detecting "entropy concentration" of [4]. The main novelty comes in a bootstrap procedure which allows the Challenge-Response mechanism of [4] to be used with sources of less and less entropy, using recursive calls to itself. Subtleties arise since the success of this mechanism depends on restricting the given sources, and so recursion constantly changes the original sources. These are resolved via a new construct, in between a disperser and an extractor, which behaves like an extractor on sufficiently large subsources of the given ones. This version is only an extended abstract, please see the full version, available on the authors' homepages, for more details.

AB - The main result of this paper is an explicit disperser for two independent sources on n bits, each of entropy k = no(1). Put differently, setting N = T and K = 2 n, we construct explicit N × N Boolean matrices for which no K × K submatrix is monochromatic. Viewed as adjacency matrices of bipartite graphs, this gives an explicit construction of K-Ramsey bipartite graphs of size N. This greatly improves the previous bound of k = o(n) of Barak, Kindler, Shaltiel, Sudakov and Wigderson [4]. It also significantly improves the 25-year record of k = Õ(√n) on the special case of Ramsey graphs, due to Frankl and Wilson [9]. The construction uses (besides "classical" extractor ideas) almost all of the machinery developed in the last couple of years for extraction from independent sources, including: Bourgain's extractor for 2 independent sources of some entropy rate < 1/2 [5] Raz's extractor for 2 independent sources, one of which has any entropy rate > 1/2 [18] Rao's extractor for 2 independent block-sources of entropy n Ω(1) [17] The "Challenge-Response" mechanism for detecting "entropy concentration" of [4]. The main novelty comes in a bootstrap procedure which allows the Challenge-Response mechanism of [4] to be used with sources of less and less entropy, using recursive calls to itself. Subtleties arise since the success of this mechanism depends on restricting the given sources, and so recursion constantly changes the original sources. These are resolved via a new construct, in between a disperser and an extractor, which behaves like an extractor on sufficiently large subsources of the given ones. This version is only an extended abstract, please see the full version, available on the authors' homepages, for more details.

KW - Dispersers

KW - Extractors

KW - Independent Sources

KW - Ramsey Graphs

UR - http://www.scopus.com/inward/record.url?scp=33748118575&partnerID=8YFLogxK

M3 - Conference contribution

AN - SCOPUS:33748118575

SN - 1595931341

SN - 9781595931344

T3 - Proceedings of the Annual ACM Symposium on Theory of Computing

SP - 671

EP - 680

BT - STOC'06

T2 - 38th Annual ACM Symposium on Theory of Computing, STOC'06

Y2 - 21 May 2006 through 23 May 2006

ER -