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We investigate offline and online algorithms for Round - UFPP , the problem of minimizing the number of rounds required to schedule a set of unsplittable flows of non-uniform size on a given path with heterogeneous edge capacities. Round - UFPP is known to be NP-hard and there are constant-factor approximation algorithms under the no bottleneck assumption (NBA), which stipulates that maximum size of any flow is at most the minimum global edge capacity. In this work, we present improved online and offline algorithms for Round - UFPP without the NBA. We first study offline Round - UFPP for a restricted class of instances, called α -small, where the size of each flow is at most α times the capacity of its bottleneck edge, and present an O (log (1 / (1 - α))) -approximation algorithm. Next, our main result is an online O (log log c max) -competitive algorithm for Round - UFPP where c max is the largest edge capacity, improving upon the previous best bound of O (log c max) due to Epstein et al. (SIAM J Discrete Math 23(2):822–841, 2009). These new results lead to an offline O (min (log n , log m , log log c max)) -approximation algorithm and an online O (min (log m , log log c max)) -competitive algorithm for Round - UFPP , where n is the number of flows and m is the number of edges. [ABSTRACT FROM AUTHOR]

The terminal backup problems ([E. Anshelevich and A. Karagiozova, SIAM J. Comput., 40 (2011), pp. 678--708]) form a class of network design problems: Given an undirected graph with a requirement on terminals, the goal is to find a minimum-cost subgraph satisfying the connectivity requirement. The node-connectivity terminal backup problem requires a terminal to connect other terminals with a number of node-disjoint paths. This problem is not known whether is NP-hard or tractable. Fukunaga [SIAM J. Discrete Math., 30 (2016), pp. 777--800] gave a 4/3-approximation algorithm based on an LP-rounding scheme using a general LP-solver. In this paper, we develop a combinatorial algorithm for the relaxed LP to find a half-integral optimal solution in O(mlog(n-A · MF(/cn,m T/c2n)) time, where n is the number of nodes, m is the number of edges, k is the number of terminals, A is the maximum edge-cost, U is the maximum edge-capacity, and MF(nz,mz) is the time complexity of a max-flow algorithm in a network with nz nodes and m' edges. The algorithm implies that the 4/3-approximation algorithm for the node-connectivity terminal backup problem is also efficiently implemented. For the design of algorithm, we explore a connection between the node-connectivity terminal backup problem and a new type of a multiflow, which is called a separately capacitated multiflow. We show a min-max theorem which extends the Lovasz-Cherkassky theorem to the node-capacity setting. Our results build on discrete convexity in the node-connectivity terminal backup problem. [ABSTRACT FROM AUTHOR]

The characterization of all the constraint satisfaction problems solvable by local consistency checking (also known as CSPs of bounded width) was proposed by Feder and Vardi [SIAM J. Comput., 28 (1998), pp. 57104]. It was confirmed by two independent proofs by Bulatov [Bounded Relational Width, manuscript, 2009] and Barto and Kozik [L. Barto and M. Kozik, 50th Annual IEEE Symposium on Foundations of Computer Science, 2009, pp. 595 603], [L. Barto and M. Kozik, J. ACM, 61 (2014), 3]. Later Barto [J. Logic Comput., 26 (2014), pp. 923 943] proved a collapse of the hierarchy of local consistency notions by showing that (2; 3) minimality solves all the CSPs of bounded width. In this paper we present a new consistency notion, jpq consistency, which also solves all the CSPs of bounded width. Our notion is strictly weaker than (2; 3) consistency, (2; 3) minimality, path consistency, and singleton arc consistency (SAC). This last fact allows us to answer the question of Chen, Dalmau, and Gruien [J. Logic Comput., 23 (2013), pp. 87 108] by confirming that SAC solves all the CSPs of bounded width. Moreover, as known algorithms work faster for SAC, the result implies that CSPs of bounded width can be, in practice, solved more efficiently. The definition of jpq consistency is closely related to a consistency condition obtained from the rounding of an SDP relaxation of a CSP instance. In fact, the main result of this paper is used by Dalmau et al. [Proceedings of the 28th Annual ACM-SIAM Symposium on Discrete Algorithms, SIAM, Philadelphia, ACM, New York, 2017, pp. 340{357] to show that CSPs with near unanimity polymorphisms admit robust approximation algorithms with polynomial loss. Finally, an algebraic characterization of some term conditions satisfied in algebras associated with templates of bounded width, first proved by Brady, is a direct consequence of our result. [ABSTRACT FROM AUTHOR]

Submodularity is one of the most important properties in combinatorial optimization, and k-submodularity is a generalization of submodularity. Maximization of a k-submodular function requires an exponential number of value oracle queries, and approximation algorithms have been studied. For unconstrained k-submodular maximization, Iwata, Tanigawa, and Yoshida, [Improved approximation algorithms for k-submodular function maximization, in Proceedings of the Twenty-Seventh Annual ACM-SIAM Symposium on Discrete Algorithms, SIAM, Philadelphia, 2016, pp. 404-413] gave a randomized k/(2k 1)-approximation algorithm for monotone functions and a randomized 1/2-approximation algorithm for nonmonotone functions. In this paper, we present improved randomized algorithms for nonmonotone functions. Our algorithm gives a k2+1 2k2+1 -approximation for k geq 3. We also give a randomized surd 17 3 2 -approximation algorithm for k = 3. We use the same framework used in Iwata, Tanigawa, and Yoshida, [Improved approximation algorithms for k-submodular function maximization, in Proceedings of the Twenty-Seventh Annual ACM-SIAM Symposium on Discrete Algorithms, SIAM, Philadelphia, 2016, pp. 404--413] and Ward and v Zivn'y [ACM Trans. Algorithms, 12 (2016), pp. 46:1--47:26] with different probabilities. [ABSTRACT FROM AUTHOR]

We consider approximation algorithms for packing integer programs (PIPs) of the form max { ⟨ c , x ⟩ : A x ≤ b , x ∈ { 0 , 1 } n } where A, b and c are nonnegative. We let W = min i , j b i / A i , j denote the width of A which is at least 1. Previous work by Bansal et al. (Theory Comput 8(24):533–565, 2012) obtained an Ω (1 Δ 0 1 / ⌊ W ⌋ ) -approximation ratio where Δ 0 is the maximum number of nonzeroes in any column of A (in other words the ℓ 0 -column sparsity of A). They raised the question of obtaining approximation ratios based on the ℓ 1 -column sparsity of A (denoted by Δ 1 ) which can be much smaller than Δ 0 . Motivated by recent work on covering integer programs (Chekuri and Quanrud, in: Proceedings of the Thirtieth Annual ACM-SIAM Symposium on Discrete Algorithms, pp 1596–1615. SIAM, 2019; Chen et al., in: Proceedings of the Twenty-seventh Annual ACM-SIAM Symposium on Discrete Algorithms, pp 1984–2003. SIAM, 2016) we show that simple algorithms based on randomized rounding followed by alteration, similar to those of Bansal et al. (Theory Comput 8(24):533–565, 2012) (but with a twist), yield approximation ratios for PIPs based on Δ 1 . First, following an integrality gap example from (Theory Comput 8(24):533–565, 2012), we observe that the case of W = 1 is as hard as maximum independent set even when Δ 1 ≤ 2 . In sharp contrast to this negative result, as soon as width is strictly larger than one, we obtain positive results via the natural LP relaxation. For PIPs with width W = 1 + ϵ where ϵ ∈ (0 , 1 ] , we obtain an Ω (ϵ 2 / Δ 1) -approximation. In the large width regime, when W ≥ 2 , we obtain an Ω ((1 1 + Δ 1 / W) 1 / (W - 1)) -approximation. We also obtain a (1 - ϵ) -approximation when W = Ω (log (Δ 1 / ϵ) ϵ 2) . Viewing the rounding algorithms as contention resolution schemes, we obtain approximation algorithms in the more general setting when the objective is a non-negative submodular function. [ABSTRACT FROM AUTHOR]

We revisit the classic problem of estimating the moments of the degree distribution of an undirected simple graph. Consider an undirected simple graph G = (V,E) with n (nonisolated) vertices, and define (for s > 0) Ms =\sum v\in V ds v. Our aim is to estimate Ms within a multiplicative error of (1 +\varepsilon) (for a given approximation parameter\varepsilon > 0) in sublinear time. We consider the sparse-graph model that allows access to uniform random vertices, queries for the degree of any vertex, and queries for a neighbor of any vertex. For the case of s = 1 (the average degree), O\ast (\surd n) queries suffice for any constant\varepsilon [U. Feige, SIAM J. Comput., 35 (2006), pp. 964--984], [O. Goldreich and D. Ron, Random Structures Algorithms, 32 (2008), pp. 473--493]. (We use the O\ast notation to suppress dependencies in log n and 1/\varepsilon.) Gonen, Ron, and Shavitt [SIAM J. Discrete Math., 25 (2011), pp. 1365--1411] extended this result to all integral s > 0 by designing an algorithm that performs O\ast (n1 1/(s+1)) queries. (Strictly speaking, their algorithm approximates the number of star-subgraphs of a given size, but a slight modification gives an algorithm for moments.) We design a new, significantly simpler algorithm for this problem. In the worst case, it exactly matches the bounds of Gonen, Ron, and Shavitt and has a much simpler proof. More importantly, the running time of this algorithm is connected to the arboricity of G. This is (essentially) the maximum density of an induced subgraph. For the family of graphs with arboricity at most\alpha, it has a query complexity of O\ast\bigl(n\cdot\alpha 1/s M 1/s s + min\bigl\{ m M 1/s s, m\cdot ns 1 Ms\bigr\}\bigr) which is always upper bounded by O\ast\bigl(n\alpha M 1/s s\bigr). Thus, for the class of constant-arboricity graphs (which includes, among others, all minor-closed families and preferential attachment graphs), we can estimate the average degree in O\ast (1) queries, and we can estimate the variance of the degree distribution in O\ast (\surd n) queries. This is a major improvement over the previous worst-case bounds. [ABSTRACT FROM AUTHOR]

We consider the problem of designing truthful mechanisms for scheduling n tasks on a set of m parallel related machines in order to minimize the makespan. In what follows, we consider that each task is owned by a selfish agent. This is a variant of the KP-model introduced by Koutsoupias and Papadimitriou (Proc. of STACS 1999, pp. 404–413, ) (and of the CKN-model of Christodoulou et al. in Proc. of ICALP 2004, pp. 345–357, ) in which the agents cannot choose the machine on which their tasks will be executed. This is done by a centralized authority, the scheduler. However, the agents may manipulate the scheduler by providing false information regarding the length of their tasks. We introduce the notion of increasing algorithm and a simple reduction that transforms any increasing algorithm into a truthful one. Furthermore, we show that some of the classical scheduling algorithms are indeed increasing: the LPT algorithm, the PTAS of Graham (SIAM J. Appl. Math. 17(2):416–429, ) in the case of two machines, as well as a simple PTAS for the case of m machines, with m a fixed constant. Our results yield a randomized r(1+ ε)-approximation algorithm where r is the ratio between the largest and the smallest speed of the related machines. Furthermore, by combining our approach with the classical result of Shmoys et al. (SIAM J. Comput. 24(6):1313–1331, ), we obtain a randomized 2 r(1+ ε)-competitive algorithm. It has to be noticed that these results are obtained without payments, unlike most of the existing works in the field of Mechanism Design. Finally, we show that if payments are allowed then our approach gives a (1+ ε)-algorithm for the off-line case with related machines. [ABSTRACT FROM AUTHOR]