Analysis of large-scale networks for different structural patterns (also called motifs) remains an active area of research in the domain of graph data management and mining. In the past three decades, research has led...
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We present a new flow framework for separation logic reasoning about programs that manipulate general graphs. The framework overcomes problems in earlier developments: it is based on standard fixed point theory, guara...
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ISBN:
(纸本)9783031308222;9783031308239
We present a new flow framework for separation logic reasoning about programs that manipulate general graphs. The framework overcomes problems in earlier developments: it is based on standard fixed point theory, guarantees least flows, rules out vanishing flows, and has an easy to understand notion of footprint as needed for soundness of the frame rule. In addition, we present algorithms for automating the frame rule, which we evaluate on graph updates extracted from linearizability proofs for concurrent data structures. The evaluation demonstrates that our algorithms help to automate key aspects of these proofs that have previously relied on user guidance or heuristics.
We provide the first deterministic data structure that given a weighted undirected graph undergoing edge insertions, processes each update with polylogarithmic amortized update time and answers queries for the distanc...
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ISBN:
(纸本)9781450399135
We provide the first deterministic data structure that given a weighted undirected graph undergoing edge insertions, processes each update with polylogarithmic amortized update time and answers queries for the distance between any pair of vertices in the current graph with a polylogarithmic approximation in O(log log n) time. Prior to this work, no data structure was known for partially dynamic graphs, i.e., graphs undergoing either edge insertions or deletions, with less than n(o(1)) update time except for dense graphs, even when allowing randomization against oblivious adversaries or considering only single-source distances.
This paper proposes an algorithmic framework for solving various combinatorial reconfiguration problems by using zero-suppressed binary decision diagrams (ZDDs), a data structure for representing families of sets. In ...
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ISBN:
(数字)9783031332715
ISBN:
(纸本)9783031332708;9783031332715
This paper proposes an algorithmic framework for solving various combinatorial reconfiguration problems by using zero-suppressed binary decision diagrams (ZDDs), a data structure for representing families of sets. In general, a reconfiguration problem checks if there is a step-by-step transformation between two given feasible solutions (e.g., independent sets of an input graph) of a fixed search problem, such that all intermediate results are also feasible and each step obeys a fixed reconfiguration rule (e.g., adding/removing a single vertex to/from an independent set). The solution space formed by all feasible solutions can be exponential in the input size, and indeed, many reconfiguration problems are known to be PSPACE-complete. This paper shows that an algorithm in the proposed framework efficiently conducts breadth-first search by compressing the solution space using ZDDs, and that it finds a shortest transformation between two given feasible solutions if such a transformation exists. Moreover, the proposed framework provides rich information on the solution space, such as its connectivity and all feasible solutions that are reachable from a specified one. Finally, we demonstrate that the proposed framework can be applied to various reconfiguration problems, and experimentally evaluate its performance.
In this work we revisit the fundamental Single-Source Shortest Paths (SSSP) problem with possibly negative edge weights. A recent breakthrough result by Bernstein, Nanongkai and Wulff-Nilsen established a near-linear ...
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ISBN:
(纸本)9798350318944
In this work we revisit the fundamental Single-Source Shortest Paths (SSSP) problem with possibly negative edge weights. A recent breakthrough result by Bernstein, Nanongkai and Wulff-Nilsen established a near-linear O(m log(8) (n) log(W))-time algorithm for negative-weight SSSP, where W is an upper bound on the magnitude of the smallest negative-weight edge. In this work we improve the running time to O(m log(2) (n) log(nW) log log n), which is an improvement by nearly six log-factors. Some of these log-factors are easy to shave (e.g. replacing the priority queue used in Dijkstra's algorithm), while others are significantly more involved (e.g. to find negative cycles we design an algorithm reminiscent of noisy binary search and analyze it with drift analysis). As side results, we obtain an algorithm to compute the minimum cycle mean in the same running time as well as a new construction for computing Low-Diameter Decompositions in directed graphs.
We develop and extensively evaluate highly scalable distributed-memory algorithms for computing minimum spanning trees (MSTs). At the heart of our solutions is a scalable variant of Bor degrees uvka's algorithm. F...
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ISBN:
(纸本)9798350337662
We develop and extensively evaluate highly scalable distributed-memory algorithms for computing minimum spanning trees (MSTs). At the heart of our solutions is a scalable variant of Bor degrees uvka's algorithm. For partitioned graphs with many local edges we improve this with an effective form of contracting local parts of the graph during a preprocessing step. We also adapt the filtering concept of the best practical sequential algorithm to develop a massively parallel Filter-Bor degrees uvka algorithm that is very useful for graphs with poor locality and high average degree. Our experiments indicate that our algorithms scale well up to at least 65 536 cores and are up to 800 times faster than previous distributed MST algorithms.
For a graph G, a D-diameter-reducing exact hopset is a small set of additional edges H that, when added to G, maintains its graph metric but guarantees that all node pairs have a shortest path in G boolean OR H using ...
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ISBN:
(纸本)9798350318944
For a graph G, a D-diameter-reducing exact hopset is a small set of additional edges H that, when added to G, maintains its graph metric but guarantees that all node pairs have a shortest path in G boolean OR H using at most D edges. A shortcut set is the analogous concept for reachability rather than distances. These objects have been studied since the early '90s, due to applications in parallel, distributed, dynamic, and streaming graph algorithms. For most of their history, the state-of-the-art construction for either object was a simple folklore algorithm, based on randomly sampling nodes to hit long paths in the graph. However, recent breakthroughs of Kogan and Parter [SODA '22] and Bernstein and Wein [SODA '23] have finally improved over the folklore algorithm for shortcut sets and for (1 + epsilon)-approximate hopsets. For either object, it is now known that one can use O(n) hop-edges to reduce diameter to (O) over tilde (n(1/3)), improving over the folklore diameter bound of (O) over tilde (n(1/2)). The only setting in which folklore sampling remains unimproved is for exact hopsets. Can these improvements be continued? We settle this question negatively by constructing graphs on which any exact hopset of O(n) edges has diameter (Omega) over tilde (n(1/2)). This improves on the previous lower bound of Omega(n(1/3)) by Kogan and Parter [FOCS '22]. Using similar ideas, we also polynomially improve the current lower bounds for shortcut sets, constructing graphs on which any shortcut set of O(n) edges reduces diameter to e (Omega) over tilde (n(1/4)). This improves on the previous lower bound of (Omega) over tilde (n(1/6)) by Huang and Pettie [SIAM J. Disc. Math. '18]. We also extend our constructions to provide lower bounds against O(p)-size exact hopsets and shortcut sets for other values of p;in particular, we show that folklore sampling is near-optimal for exact hopsets in the entire range of parameters p is an element of [1, n(2)].
We consider the problem of designing deterministic graph algorithms for the model of Massively Parallel Computation (MPC) that improve with the sparsity of the input graph, as measured by the standard notion of arbori...
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ISBN:
(纸本)9781450395458
We consider the problem of designing deterministic graph algorithms for the model of Massively Parallel Computation (MPC) that improve with the sparsity of the input graph, as measured by the standard notion of arboricity. For the problems of maximal independent set (MIS), maximal matching (MM), and vertex coloring, we improve the state of the art as follows. Let lambda denote the arboricity of the..-node input graph with maximum degree Delta. MIS andMM. We develop a low-space MPC algorithm that deterministically reduces the maximum degree to poly(lambda) in O(log log n) rounds, improving and simplifying the randomized O(log log n)-round poly(max(lambda, log n))-degree reduction of Ghaffari, Grunau, Jin [DISC'20]. Our approach when combined with the state-of-the-art O(log Delta + log log n)-round algorithm by Czumaj, Davies, Parter [SPAA'20, TALG'21] leads to an improved deterministic round complexity of O(log lambda + log log n). The above MIS and MM algorithm however works in the setting where the global memory allowed, i.e., the number of machines times the local memory per machine, is superlinear in the input size. We extend them to obtain the first low-space MIS and MM algorithms that work with linear global memory. Specifically, we show that both problems can be solved in deterministic time O(log lambda center dot log log(lambda) n), and even in O(log log n) time for graphs with arboricity at most log(O(1)) log n. In this setting, only a O(log(2) log n)-running time bound for trees was known due to Latypov and Uitto [ArXiv'21]. Vertex Coloring. We present a O(1)-round deterministic algorithm for the problem of O(lambda)-coloring in the linear-memory regime of MPC, with relaxed global memory of n center dot poly(lambda). This matches the round complexity of the state-of-the-art randomized algorithm by Ghaffari and Sayyadi [ICALP'19] and significantly improves upon the deterministic O(lambda(epsilon))-round algorithm by Barenboim and Khazanov [CSR'18]. Our algor
Determining the degree of inherent parallelism in classical sequential algorithms and leveraging it for fast parallel execution is a key topic in parallel computing, and detailed analyses are known for a wide range of...
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ISBN:
(纸本)9781450395458
Determining the degree of inherent parallelism in classical sequential algorithms and leveraging it for fast parallel execution is a key topic in parallel computing, and detailed analyses are known for a wide range of classical algorithms. In this paper, we perform the first such analysis for the fundamental Union-Find problem, in which we are given a graph as a sequence of edges, and must maintain its connectivity structure under edge additions. We prove that classic sequential algorithms for this problem are well-parallelizable under reasonable assumptions, addressing a conjecture by [Blelloch, 2017]. More precisely, we show via a new potential argument that, under uniform random edge ordering, parallel union-find operations are unlikely to interfere: T concurrent threads processing the graph in parallel will encounter memory contention O(T-2 center dot log vertical bar V vertical bar center dot log vertical bar E vertical bar) times in expectation, where vertical bar E vertical bar and vertical bar V vertical bar are the number of edges and nodes in the graph, respectively. We leverage this result to design a new parallel Union-Find algorithm that is both internally deterministic, i.e., its results are guaranteed to match those of a sequential execution, but also work-efficient and scalable, as long as the number of threads T is O(vertical bar E vertical bar(1/3-epsilon)), for an arbitrarily small constant epsilon > 0, which holds for most large real-world graphs. We present lower bounds which show that our analysis is close to optimal, and experimental results suggesting that the performance cost of internal determinism is limited.
Suppose that we are given a positive integer k, and a k-(vertex-)colouring f 0 of a given graph G. Then we are asked to find a colouring of G using the minimum number of colours among colourings that are reachable fro...
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Suppose that we are given a positive integer k, and a k-(vertex-)colouring f 0 of a given graph G. Then we are asked to find a colouring of G using the minimum number of colours among colourings that are reachable from f 0 by iteratively changing a colour assignment of exactly one vertex while maintaining the property of k-colourings. In this paper, we give linear-time algorithms to solve the problem for graphs of degeneracy at most two and for the case where k = 3 . These results imply linear-time algorithms for series-parallel graphs and grid graphs. In addition, we give linear-time algorithms for chordal graphs and cographs. On the other hand, we show that, for any k = 4 , this problem remains NP-hard for planar graphs with degeneracy three and maximum degree four. Thus, we obtain a complexity dichotomy for this problem with respect to the degeneracy of a graph and the number k of colours.
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