Derandomizing graph tests for homomorphism

  • Authors:
  • Angsheng Li;Linqing Tang

  • Affiliations:
  • State Key Lab. of Computer Science, Institute of Software, Chinese Academy of Sciences;State Key Lab. of Computer Science, Institute of Software, Chinese Academy of Sciences and Graduate University of Chinese Academy of Sciences

  • Venue:
  • TAMC'08 Proceedings of the 5th international conference on Theory and applications of models of computation
  • Year:
  • 2008

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Abstract

In this article, we study the randomness-efficient graph tests for homomorphism over arbitrary groups (which can be used in locally testing the Hadamard code and PCP construction). We try to optimize both the amortized-tradeoff (between number of queries and error probability) and the randomness complexity of the homomorphism test simultaneously. For an abelian group G = Zpm, by using the λ-biased set S of G, we show that, on any given bipartite graph H = (V1, V2;E), the graph test for linearity over G is a test with randomness complexity |V1| log |G| + |V2|O(log |S|), query complexity |V1| + |V2| + |E| and error probability at most p-|E| + (1 - p-|E| ċ δ for any f which is 1 - p-1(1 +√δ2-λ/2 )-far from being affine linear. For a non-abelian group G, we introduce a random walk of some length, l say, on expander graphs to design a probabilistic homomorphism test over G with randomness complexity log |G| + O(log log |G|), query complexity 2l +1 and error probability at most 1 - δ2l2/(δl+δ2l2-δ2l)+ 2ψ(λ, l) for any f which is 2δ/(1 - λ)-far from being affine homomorphism, here ψ(λ, l) = Σ0≤ij≤l-1λj-i-1.