1,178 Works

On Visibility Representations of Non-Planar Graphs

Therese Biedl, Giuseppe Liotta & Fabrizio Montecchiani
A rectangle visibility representation (RVR) of a graph consists of an assignment of axis-aligned rectangles to vertices such that for every edge there exists a horizontal or vertical line of sight between the rectangles assigned to its endpoints. Testing whether a graph has an RVR is known to be NP-hard. In this paper, we study the problem of finding an RVR under the assumption that an embedding in the plane of the input graph is...

Symbolic Lookaheads for Bottom-up Parsing

Paola Quaglia
We present algorithms for the construction of LALR(1) parsing tables, and of LR(1) parsing tables of reduced size. We first define specialized characteristic automata whose states are parametric w.r.t. variables symbolically representing lookahead-sets. The propagation flow of lookaheads is kept in the form of a system of recursive equations, which is resolved to obtain the concrete LALR(1) table. By inspection of the LALR(1) automaton and of its lookahead ropagation flow, we decide whether the grammar...

Optimal Assumptions for Synthesis

Romain Brenguier
Controller synthesis is the automatic construction a correct system from its specification. This often requires assumptions about the behaviour of the environment. It is difficult for the designer to identify the assumptions that ensures the existence of a correct controller, and doing so manually can lead to assumptions that are stronger than necessary. As a consequence the generated controllers are suboptimal in terms of robustness. In this work, given a specification, we identify the weakest...

Controlled Natural Languages for Knowledge Representation and Reasoning

Tiantian Gao
Controlled natural languages (CNLs) are effective languages for knowledge representation and reasoning. They are designed based on certain natural languages with restricted lexicon and grammar. CNLs are unambiguous and simple as opposed to their base languages. They preserve the expressiveness and coherence of natural languages. In this paper, it mainly focuses on a class of CNLs, called machine-oriented CNLs, which have well-defined semantics that can be deterministically translated into formal languages to do logical reasoning....

Reachability in Networks of Register Protocols under Stochastic Schedulers

Patricia Bouyer, Nicolas Markey, Mickael Randour, Arnaud Sangnier & Daniel Stan
We study the almost-sure reachability problem in a distributed system obtained as the asynchronous composition of N copies (called processes) of the same automaton (called protocol), that can communicate via a shared register with finite domain. The automaton has two types of transitions: write-transitions update the value of the register, while read-transitions move to a new state depending on the content of the register. Non-determinism is resolved by a stochastic scheduler. Given a protocol, we...

Interactive Geometric Algorithm Visualization in a Browser

Kirk Gardner, Lynn Asselin & Donald Sheehy
We present an online, interactive tool for writing and presenting interactive geometry demos suitable for classroom demonstrations. Code for the demonstrations is written in JavaScript using p5.js, a JavaScript library based on Processing.

Weak 1/r-Nets for Moving Points

Alexandre Rok & Shakhar Smorodinsky
In this paper, we extend the weak 1/r-net theorem to a kinetic setting where the underlying set of points is moving polynomially with bounded description complexity. We establish that one can find a kinetic analog N of a weak 1/r-net of cardinality O(r^(d(d+1)/2)log^d r) whose points are moving with coordinates that are rational functions with bounded description complexity. Moreover, each member of N has one polynomial coordinate.

Functional Lower Bounds for Arithmetic Circuits and Connections to Boolean Circuit Complexity

Michael A. Forbes, Mrinal Kumar & Ramprasad Saptharishi
We say that a circuit C over a field F {functionally} computes a polynomial P in F[x_1, x_2, ..., x_n] if for every x in {0,1}^n we have that C(x) = P(x). This is in contrast to syntactically computing P, when C = P as formal polynomials. In this paper, we study the question of proving lower bounds for homogeneous depth-3 and depth-4 arithmetic circuits for functional computation. We prove the following results: 1. Exponential...

Fixed Points of the Restricted Delaunay Triangulation Operator

Marc Khoury & Jonathan Richard Shewchuk
The restricted Delaunay triangulation can be conceived as an operator that takes as input a k-manifold (typically smooth) embedded in R^d and a set of points sampled with sufficient density on that manifold, and produces as output a k-dimensional triangulation of the manifold, the input points serving as its vertices. What happens if we feed that triangulation back into the operator, replacing the original manifold, while retaining the same set of input points? If k...

Counting Linear Extensions: Parameterizations by Treewidth

Eduard Eiben, Robert Ganian, Kustaa Kanga & Sebastian Ordyniak
We consider the #P-complete problem of counting the number of linear extensions of a poset (#LE); a fundamental problem in order theory with applications in a variety of distinct areas. In particular, we study the complexity of #LE parameterized by the well-known decompositional parameter treewidth for two natural graphical representations of the input poset, i.e., the cover and the incomparability graph. Our main result shows that #LE is fixed-parameter intractable parameterized by the treewidth of...

Dependence Logic vs. Constraint Satisfaction

Lauri Hella & Phokion G. Kolaitis
During the past decade, dependence logic has emerged as a formalism suitable for expressing and analyzing notions of dependence and independence that arise in different scientific areas. The sentences of dependence logic have the same expressive power as those of existential second-order logic, hence dependence logic captures NP on the class of all finite structures. In this paper, we identify a natural fragment of universal dependence logic and show that, in a precise sense, it...

Simulation Combined Approach to Police Patrol Services Staffing

Hanjing Zhang, Antuela Tako, Lisa M. Jackson & Jiyin Liu

New Extractors for Interleaved Sources

Eshan Chattopadhyay & David Zuckerman
We study how to extract randomness from a C-interleaved source, that is, a source comprised of C independent sources whose bits or symbols are interleaved. We describe a simple approach for constructing such extractors that yields: (1) For some delta>0, c>0, explicit extractors for 2-interleaved sources on {0,1}^{2n} when one source has min-entropy at least (1-delta)*n and the other has min-entropy at least c*log(n). The best previous construction, by Raz and Yehudayoff, worked only when...

k-Center Clustering Under Perturbation Resilience

Maria-Florina Balcan, Nika Haghtalab & Colin White
The k-center problem is a canonical and long-studied facility location and clustering problem with many applications in both its symmetric and asymmetric forms. Both versions of the problem have tight approximation factors on worst case instances: a 2-approximation for symmetric kcenter and an O(log*(k))-approximation for the asymmetric version. Therefore to improve on these ratios, one must go beyond the worst case. In this work, we take this approach and provide strong positive results both for...

The Densest Subgraph Problem with a Convex/Concave Size Function

Yasushi Kawase & Atsushi Miyauchi

The Farthest-Point Geodesic Voronoi Diagram of Points on the Boundary of a Simple Polygon

Eunjin Oh, Luis Barba & Hee-Kap Ahn
Given a set of sites (points) in a simple polygon, the farthest-point geodesic Voronoi diagram partitions the polygon into cells, at most one cell per site, such that every point in a cell has the same farthest site with respect to the geodesic metric. We present an O((n+m)loglogn)-time algorithm to compute the farthest-point geodesic Voronoi diagram for m sites lying on the boundary of a simple n-gon.

Hardness of Approximation for H-Free Edge Modification Problems

Ivan Bliznets, Marek Cygan, Pawel Komosa & Michal Pilipczuk
The H-free Edge Deletion problem asks, for a given graph G and integer k, whether it is possible to delete at most k edges from G to make it H-free, that is, not containing H as an induced subgraph. The H-free Edge Completion problem is defined similarly, but we add edges instead of deleting them. The study of these two problem families has recently been the subject of intensive studies from the point of view...

A Complexity Trichotomy for Approximately Counting List H-Colourings

Andreas Galanis, Leslie Ann Goldberg & Mark Jerrum
We examine the computational complexity of approximately counting the list H-colourings of a graph. We discover a natural graph-theoretic trichotomy based on the structure of the graph H. If H is an irreflexive bipartite graph or a reflexive complete graph then counting list H-colourings is trivially in polynomial time. Otherwise, if H is an irreflexive bipartite permutation graph or a reflexive proper interval graph then approximately counting list H-colourings is equivalent to #BIS, the problem...

An ~O(n) Queries Adaptive Tester for Unateness

Subhash Khot & Igor Shinkar
We present an adaptive tester for the unateness property of Boolean functions. Given a function f:{0,1}^n -> {0,1} the tester makes O(n log(n)/epsilon) adaptive queries to the function. The tester always accepts a unate function, and rejects with probability at least 0.9 if a function is epsilon-far from being unate.

Provably Secure Virus Detection: Using The Observer Effect Against Malware

Richard J. Lipton, Rafail Ostrovsky & Vassilis Zikas
Protecting software from malware injection is one of the biggest challenges of modern computer science. Despite intensive efforts by the scientific and engineering community, the number of successful attacks continues to increase. This work sets first footsteps towards a provably secure investigation of malware detection. We provide a formal model and cryptographic security definitions of attestation for systems with dynamic memory, and suggest novel provably secure attestation schemes. The key idea underlying our schemes is...

Testing of Concurrent Programs

Miguel Isabel
Testing concurrent systems requires exploring all possible non-deterministic interleavings that the concurrent execution may have, as any of the interleavings may reveal erroneous behaviour. This introduces a new problem: the well-known state space problem, which is often computationally intractable. In the present thesis, this issue will be addressed through: (1) the development of new Partial-Order Reduction Techniques and (2) the combination of static analysis and testing (property-based testing) in order to reduce the combinatorial explosion....

Counting Hypergraph Matchings up to Uniqueness Threshold

Renjie Song, Yitong Yin & Jinman Zhao
We study the problem of approximately counting matchings in hypergraphs of bounded maximum degree and maximum size of hyperedges. With an activity parameter lambda, each matching M is assigned a weight lambda^{|M|}. The counting problem is formulated as computing a partition function that gives the sum of the weights of all matchings in a hypergraph. This problem unifies two extensively studied statistical physics models in approximate counting: the hardcore model (graph independent sets) and the...

Atomic Snapshots from Small Registers

Leqi Zhu & Faith Ellen
Existing n-process implementations of atomic snapshots from registers use large registers. We consider the problem of implementing an m-component snapshot from small, Theta(log(n))-bit registers. A natural solution is to consider simulating the large registers. Doing so straightforwardly can significantly increase the step complexity. We introduce the notion of an interruptible read and show how it can reduce the step complexity of simulating the large registers in the snapshot of Afek et al. In particular, we...

Fast and Powerful Hashing Using Tabulation (Invited Talk)

Mikkel Thorup
Randomized algorithms are often enjoyed for their simplicity, but the hash functions employed to yield the desired probabilistic guarantees are often too complicated to be practical. Here we survey recent results on how simple hashing schemes based on tabulation provide unexpectedly strong guarantees. Simple tabulation hashing dates back to Zobrist [1970]. Keys are viewed as consisting of c characters and we have precomputed character tables h_1, ... , h_q mapping characters to random hash values....

Double-Exponential and Triple-Exponential Bounds for Choosability Problems Parameterized by Treewidth

Dániel Marx & Valia Mitsou

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