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ECCC

2006

2006

Ahlswede and Winter [AW02] introduced a Chernoff bound for matrix-valued random variables, which is a non-trivial generalization of the usual Chernoff bound for real-valued random variables. We present an efficient derandomization of their bound using the method of pessimistic estimators (see Raghavan [Rag88]). As a consequence, we derandomize a construction of Alon and Roichman [AR94] (see also [LR04, LS04]) to efficiently construct an expanding Cayley graph of logarithmic degree on any (possibly non-abelian) group. This also gives an optimal solution to the homomorphism testing problem of Shpilka and Wigderson [SW04]. We also apply these pessimistic estimators to the problem of solving semi-definite covering problems, thus giving a deterministic algorithm for the quantum hypergraph cover problem of [AW02]. The results above appear as theorems in the paper [WX05a] (see also [WX05b]), as consequences to the main theorem of that paper: a randomness efficient sampler for matrix valued f...

Added |
12 Dec 2010 |

Updated |
12 Dec 2010 |

Type |
Journal |

Year |
2006 |

Where |
ECCC |

Authors |
Avi Wigderson, David Xiao |

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