Abstract.

We determine the computational complexity of approximately counting and sampling independent sets of a given size in bounded-degree graphs. That is, we identify a critical density \(\alpha_c(\Delta )\) and provide (i) for \(\alpha \lt \alpha_c(\Delta )\) randomized polynomial-time algorithms for approximately sampling and counting independent sets of given size at most \(\alpha n\) in \(n\) -vertex graphs of maximum degree \(\Delta\) , and (ii) a proof that unless NP = RP, no such algorithms exist for \(\alpha \gt \alpha_c(\Delta )\) . The critical density is the occupancy fraction of the hard-core model on the complete graph \(K_{\Delta+1}\) at the uniqueness threshold on the infinite \(\Delta\) -regular tree, giving \(\alpha_c(\Delta )\sim \frac{e}{1+e}\frac{1}{\Delta }\) as \(\Delta \to \infty\) . Our methods apply more generally to antiferromagnetic 2-spin systems and motivate new questions in extremal combinatorics.

Keywords

  1. approximate counting
  2. sampling
  3. independent sets
  4. FPRAS
  5. hard-core model
  6. computational threshold

MSC codes

  1. 68Q17
  2. 68Q25
  3. 68Q87
  4. 05C30

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Information & Authors

Information

Published In

cover image SIAM Journal on Computing
SIAM Journal on Computing
Pages: 618 - 640
ISSN (online): 1095-7111

History

Submitted: 17 December 2021
Accepted: 23 January 2023
Published online: 26 April 2023

Keywords

  1. approximate counting
  2. sampling
  3. independent sets
  4. FPRAS
  5. hard-core model
  6. computational threshold

MSC codes

  1. 68Q17
  2. 68Q25
  3. 68Q87
  4. 05C30

Authors

Affiliations

Ewan Davies Contact the author
Corresponding author. Department of Computer Science, Colorado State University, Fort Collins, CO 80523 USA.
Will Perkins
School of Computer Science, Georgia Institute of Technology, Atlanta, GA 30332 USA.

Funding Information

National Science Foundation (NSF): DMS-1847451, CCF-1934915
Funding: The second author was supported in part by NSF grants DMS-1847451 and CCF-1934915.

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