| 1. |
- De Rezende, Susanna F., et al.
(författare)
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KRW composition theorems via lifting
- 2020
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Ingår i: Proceedings - 2020 IEEE 61st Annual Symposium on Foundations of Computer Science, FOCS 2020. - 0272-5428. - 9781728196213 - 9781728196220 ; 2020-November, s. 43-49
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Konferensbidrag (refereegranskat)abstract
- One of the major open problems in complexity theory is proving super-logarithmic lower bounds on the depth of circuits (i.e., mathrm{P} nsubseteq text{NC}{1}). Karchmer, Raz, and Wigderson [13] suggested to approach this problem by proving that depth complexity behaves'as expected' with respect to the composition of functions f diamond g. They showed that the validity of this conjecture would imply that mathrm{P} nsubseteq text{NC}{1}. Several works have made progress toward resolving this conjecture by proving special cases. In particular, these works proved the KRW conjecture for every outer function, but only for few inner functions. Thus, it is an important challenge to prove the KRW conjecture for a wider range of inner functions. In this work, we extend significantly the range of inner functions that can be handled. First, we consider the monotone version of the KRW conjecture. We prove it for every monotone inner function whose depth complexity can be lower bounded via a query-to-communication lifting theorem. This allows us to handle several new and well-studied functions such as the s-t-connectivity, clique, and generation functions. In order to carry this progress back to the non-monotone setting, we introduce a new notion of semi-monotone composition, which combines the non-monotone complexity of the outer function with the monotone complexity of the inner function. In this setting, we prove the KRW conjecture for a similar selection of inner functions, but only for a specific choice of the outer function f.
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| 2. |
- De Rezende, Susanna, et al.
(författare)
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Lifting with simple gadgets and applications to circuit and proof complexity
- 2020
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Ingår i: Proceedings - 2020 IEEE 61st Annual Symposium on Foundations of Computer Science, FOCS 2020. - 0272-5428. - 9781728196213 - 9781728196220 ; 2020-November, s. 24-30
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Konferensbidrag (refereegranskat)abstract
- We significantly strengthen and generalize the theorem lifting Nullstellensatz degree to monotone span program size by Pitassi and Robere (2018) so that it works for any gadget with high enough rank, in particular, for useful gadgets such as equality and greater-than. We apply our generalized theorem to solve three open problems: •We present the first result that demonstrates a separation in proof power for cutting planes with unbounded versus polynomially bounded coefficients. Specifically, we exhibit CNF formulas that can be refuted in quadratic length and constant line space in cutting planes with unbounded coefficients, but for which there are no refutations in subexponential length and subpolynomial line space if coefficients are restricted to be of polynomial magnitude. •We give the first explicit separation between monotone Boolean formulas and monotone real formulas. Specifically, we give an explicit family of functions that can be computed with monotone real formulas of nearly linear size but require monotone Boolean formulas of exponential size. Previously only a non-explicit separation was known. •We give the strongest separation to-date between monotone Boolean formulas and monotone Boolean circuits. Namely, we show that the classical GEN problem, which has polynomial-size monotone Boolean circuits, requires monotone Boolean formulas of size 2{Omega(n text{polylog}(n))}. An important technical ingredient, which may be of independent interest, is that we show that the Nullstellensatz degree of refuting the pebbling formula over a DAG G over any field coincides exactly with the reversible pebbling price of G. In particular, this implies that the standard decision tree complexity and the parity decision tree complexity of the corresponding falsified clause search problem are equal. This is an extended abstract. The full version of the paper is available at https://arxiv.org/abs/2001.02144.
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| 3. |
- Björklund, Andreas, et al.
(författare)
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Computing the Tutte polynomial in vertex-exponential time
- 2008
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Ingår i: Proceedings of the 49th Annual IEEE Symposium on Foundations of Computer Science. - 0272-5428. ; , s. 677-686
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Konferensbidrag (refereegranskat)abstract
- The deletion-contraction algorithm is perhaps the most popular method for computing a host of fundamental graph invariants such as the chromatic, flow, and reliability polynomials in graph theory, the Jones polynomial of an alternating link in knot theory, and the partition functions of the models of Ising, Potts, and Fortuin-Kasteleyn in statistical physics. Prior to this work, deletion-contraction was also the fastest known general-purpose algorithm for these invariants, running in time roughly proportional to the number of spanning trees in the input graph. Here, we give a substantially faster algorithm that computes the Tutte polynomial-and hence, all the aforementioned invariants and more-of an arbitrary graph in time within a polynomial factor of the number of connected vertex sets. The algorithm actually evaluates a multivariate generalization of the Tutte polynomial by making use of an identity due to Fortuin and Kasteleyn. We also provide a polynomial-space variant of the algorithm and give an analogous result for Chung and Graham's cover polynomial.
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| 4. |
- Björklund, Andreas
(författare)
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Determinant sums for undirected Hamiltonicity
- 2010
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Ingår i: 2010 IEEE 51st Annual Symposium On Foundations Of Computer Science. - 0272-5428. - 9780769542447 ; , s. 173-182
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Konferensbidrag (refereegranskat)abstract
- Abstract in UndeterminedWe present a Monte Carlo algorithm for Hamiltonicity detection in an n-vertex undirected graph running in O*(1.657(n)) time. To the best of our knowledge, this is the first superpolynomial improvement on the worst case runtime for the problem since the O*(2(n)) bound established for TSP almost fifty years ago (Bellman 1962, Held and Karp 1962). It answers in part the first open problem in Woeginger's 2003 survey on exact algorithms for NP-hard problems.For bipartite graphs, we improve the bound to O*(1.414(n)) time. Both the bipartite and the general algorithm can be implemented to use space polynomial in n.We combine several recently resurrected ideas to get the results. Our main technical contribution is a new reduction inspired by the algebraic sieving method for k-Path (Koutis ICALP 2008, Williams IPL 2009). We introduce the Labeled Cycle Cover Sum in which we are set to count weighted arc labeled cycle covers over a finite field of characteristic two. We reduce Hamiltonicity to Labeled Cycle Cover Sum and apply the determinant summation technique for Exact Set Covers (Bjorklund STACS 2010) to evaluate it.
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| 5. |
- Björklund, Andreas, et al.
(författare)
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The Parity of Directed Hamiltonian Cycles
- 2013
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Ingår i: Annual IEEE Symposium on Foundations of Computer Science. - 0272-5428. ; , s. 727-735
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Konferensbidrag (refereegranskat)abstract
- We present a deterministic algorithm that given any directed graph on n vertices computes the parity of its number of Hamiltonian cycles in O(1.619n) time and polynomial space. For bipartite graphs, we give a 1.5npoly(n) expected time algorithm. Our algorithms are based on a new combinatorial formula for the number of Hamiltonian cycles modulo a positive integer.
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| 6. |
- Conneryd, Jonas, et al.
(författare)
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Graph Colouring Is Hard on Average for Polynomial Calculus and Nullstellensatz
- 2023
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Ingår i: Proceedings - 2023 IEEE 64th Annual Symposium on Foundations of Computer Science, FOCS 2023. - 0272-5428. - 9798350318944 ; , s. 1-11
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Konferensbidrag (refereegranskat)abstract
- We prove that polynomial calculus (and hence also Nullstellensatz) over any field requires linear degree to refute that sparse random regular graphs, as well as sparse Erdős-Rényi random graphs, are 3-colourable.
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| 7. |
- De Rezende, Susanna F., et al.
(författare)
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Clique Is Hard on Average for Unary Sherali-Adams
- 2023
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Ingår i: Proceedings - 2023 IEEE 64th Annual Symposium on Foundations of Computer Science, FOCS 2023. - 0272-5428. - 9798350318944 ; , s. 12-25
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Konferensbidrag (refereegranskat)abstract
- We prove that unary Sherali-Adams requires proofs of size nΩ(d) to rule out the existence of an nΘ(1)-clique in Erdős-Rényi random graphs whose maximum clique is of size d ≤ 2 log n. This lower bound is tight up to the multiplicative constant in the exponent. We obtain this result by introducing a technique inspired by pseudo-calibration which may be of independent interest. The technique involves defining a measure on monomials that precisely captures the contribution of a monomial to a refutation. This measure intuitively captures progress and should have further applications in proof complexity.
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| 8. |
- Isaksson, Marcus, 1978, et al.
(författare)
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The geometry of manipulation - A quantitative proof of the gibbard satterthwaite theorem
- 2010
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Ingår i: 2010 IEEE 51st Annual Symposium on Foundations of Computer Science, FOCS 2010; Las Vegas, NV; 23 October 2010 through 26 October 2010. - 0272-5428. - 9780769542447 ; :Article number 5671191, s. 319-328
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Konferensbidrag (refereegranskat)abstract
- We prove a quantitative version of the Gibbard-Satterthwaite theorem. We show that a uniformly chosen voter profile for a neutral social choice function f of q >= 4 alternatives and n voters will be manipulable with probability at least 10(-4)epsilon(2)n(-3)q(-30), where epsilon is the minimal statistical distance between f and the family of dictator functions. Our results extend those of [1], which were obtained for the case of 3 alternatives, and imply that the approach of masking manipulations behind computational hardness (as considered in [2], [3], [4], [5], [6]) cannot hide manipulations completely. Our proof is geometric. More specifically it extends the method of canonical paths to show that the measure of the profiles that lie on the interface of 3 or more outcomes is large. To the best of our knowledge our result is the first isoperimetric result to establish interface of more than two bodies.
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