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Decodability of group homomorphisms beyond the johnson bound
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Annual ACM Symposium on Theory of Computing archive
Proceedings of the 40th annual ACM symposium on Theory of computing table of contents
Victoria, British Columbia, Canada
SESSION: 7A table of contents
Pages 275-284  
Year of Publication: 2008
ISBN:978-1-60558-047-0
Authors
Irit Dinur  Weizmann Institute of Science, Rehovot, Israel
Elena Grigorescu  Massachusetts Institute of Technology, Cambridge, MA, USA
Swastik Kopparty  Massachusetts Institute of Technology, Cambridge, MA, USA
Madhu Sudan  Massachusetts Institute of Technology, Cambridge, MA, USA
Sponsors
ACM: Association for Computing Machinery
SIGACT: ACM Special Interest Group on Algorithms and Computation Theory
Publisher
ACM  New York, NY, USA
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ABSTRACT

Given a pair of finite groups G and H, the set of homomorphisms from G to H form an error-correcting code where codewords differ in at least 1/2 the coordinates. We show that for every pair of abelian groups G and H, the resulting code is (locally) list-decodable from a fraction of errors arbitrarily close to its distance. At the heart of this result is the following combinatorial result: There is a fixed polynomial p(•) such that for every pair of abelian groups G and H, if the maximum fraction of agreement between two distinct homomorphisms from G to H is Λ, then for every ε> 0 and every function f:G -> H, the number of homomorphisms that have agreement Λ + ε with f is at most p(1/ε). We thus give a broad class of codes whose list-decoding radius exceeds the "Johnson bound". Examples of such codes are rare in the literature, and for the ones that do exist, "combinatorial" techniques to analyze their list-decodability are limited. Our work is an attempt to add to the body of such techniques. We use the fact that abelian groups decompose into simpler ones and thus codes derived from homomorphisms over abelian groups may be viewed as certain "compositions" of simpler codes. We give techniques to lift list-decoding bounds for the component codes to bounds for the composed code. We believe these techniques may be of general interest.


REFERENCES

Note: OCR errors may be found in this Reference List extracted from the full text article. ACM has opted to expose the complete List rather than only correct and linked references.

 
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Irit Dinur, Elena Grigorescu, Swastik Kopparty, and Madhu Sudan. Decodability of Group Homomorphisms beyond the Johnson Bound. Electronic Colloquium on Computational Complexity (ECCC), 15(TR08-020), 2008.
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Elena Grigorescu, Swastik Kopparty, and Madhu Sudan. Local decoding and testing for homomorphisms. In APPROX-RANDOM, volume 4110 of Lecture Notes in Computer Science, pages 375--385. Springer, 2006.
 
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V. Guruswami and M. Sudan. Extensions to the johnson bound, 2001.
 
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Venkatesan Guruswami and Atri Rudra. Explicit capacity-achieving list-decodable codes. Electronic Colloquium on Computational Complexity (ECCC), (133), 2005.
 
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Serge Lang. Algebra. Addison-Wesley, 1965.
 
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A. Ta-Shma and D. Zuckerman. Extractor codes. IEEE Transactions on Information Theory, 50, 2004


Collaborative Colleagues:
Irit Dinur: colleagues
Elena Grigorescu: colleagues
Swastik Kopparty: colleagues
Madhu Sudan: colleagues