Author

# Camil Demetrescu

Other affiliations: University of Rome Tor Vergata

Bio: Camil Demetrescu is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Shortest Path Faster Algorithm & Shortest path problem. The author has an hindex of 27, co-authored 96 publications receiving 2938 citations. Previous affiliations of Camil Demetrescu include University of Rome Tor Vergata.

##### Papers published on a yearly basis

##### Papers

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TL;DR: A fully dynamic algorithm for general directed graphs with non-negative real-valued edge weights that supports any sequence of operations in O(n2log3n) amortized time per update and unit worst-case time per distance query, where n is the number of vertices.

Abstract: We study novel combinatorial properties of graphs that allow us to devise a completely new approach to dynamic all pairs shortest paths problems. Our approach yields a fully dynamic algorithm for general directed graphs with non-negative real-valued edge weights that supports any sequence of operations in O(n2log3n) amortized time per update and unit worst-case time per distance query, where n is the number of vertices. We can also report shortest paths in optimal worst-case time. These bounds improve substantially over previous results and solve a long-standing open problem. Our algorithm is deterministic, uses simple data structures, and appears to be very fast in practice.

294 citations

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TL;DR: A survey of the main challenges, challenges, and solutions for symbolic execution can be found in this paper, where the authors provide an overview of main ideas, challenges and solutions developed in the area.

Abstract: Many security and software testing applications require checking whether certain properties of a program hold for any possible usage scenario. For instance, a tool for identifying software vulnerabilities may need to rule out the existence of any backdoor to bypass a program’s authentication. One approach would be to test the program using different, possibly random inputs. As the backdoor may only be hit for very specific program workloads, automated exploration of the space of possible inputs is of the essence. Symbolic execution provides an elegant solution to the problem, by systematically exploring many possible execution paths at the same time without necessarily requiring concrete inputs. Rather than taking on fully specified input values, the technique abstractly represents them as symbols, resorting to constraint solvers to construct actual instances that would cause property violations. Symbolic execution has been incubated in dozens of tools developed over the past four decades, leading to major practical breakthroughs in a number of prominent software reliability applications. The goal of this survey is to provide an overview of the main ideas, challenges, and solutions developed in the area, distilling them for a broad audience.

271 citations

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01 Feb 2010

TL;DR: In this article, the authors present dynamic algorithms for undirected graphs in Section 9.2 and describe some open problems in the context of dynamic graph problems, including insertions and deletions of vertices.

Abstract: In many applications of graph algorithms, including communication networks, graphics, assembly
planning, and VLSI design, graphs are subject to discrete changes, such as additions or deletions of
edges or vertices. In the last decades there has been a growing interest in such dynamically changing
graphs, and a whole body of algorithms and data structures for dynamic graphs has been discovered.
This chapter is intended as an overview of this ﬁeld.
In a typical dynamicgraphproblemonewould like to answerqueries ongraphs that areundergoinga sequence of updates, for instance, insertions and deletions of edges and vertices. The goal of a
dynamic graph algorithm is to update eﬃciently the solution of a problem after dynamic changes,
rather than having to recompute it from scratch each time. Given their powerful versatility, it is not
surprising that dynamic algorithms and dynamic data structures are often more diﬃcult to design
and analyze than their static counterparts.
We can classify dynamic graph problems according to the types of updates allowed. A problemis said to be fully dynamic if the update operations include unrestricted insertions and deletions of
edges. A problem is called partially dynamic if only one type of update, either insertions or deletions,
is allowed. If only insertions are allowed, the problem is called incremental; if only deletions are
allowed it is called decremental.
In this chapter, we describe fully dynamic algorithms for graph problems. We present dynamicalgorithms for undirected graphs in Section 9.2. Dynamic algorithms for directed graphs are next
described in Section 9.3. Finally, in Section 9.4 we describe some open problems.

229 citations

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09 Jun 2003TL;DR: A fully dynamic algorithm for general directed graphs with non-negative real-valued edge weights that supports any sequence of operations in amortized time per update and unit worst-case time per distance query, where n is the number of vertices.

Abstract: We study novel combinatorial properties of graphs that allow us to devise a completely new approach to dynamic all pairs shortest paths problems. Our approach yields a fully dynamic algorithm for general directed graphs with non-negative real-valued edge weights that supports any sequence of operations in O(n2) amortized time per update and unit worst-case time per distance query, where n is the number of vertices. We can also report shortest paths in optimal worst-case time. These bounds improve substantially over previous results and solve a long-standing open problem. Our algorithm is deterministic and uses simple data structures.

189 citations

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28 Jul 2009

TL;DR: The purpose of the shortest-path algorithm is to calculate the distance of the longest path from v to each of the reachable nodes of the graph, which is the sum of the weights of the edges on the path.

Abstract: Shortest path problems are among the most fundamental combinatorial optimization problems with many applications, both direct and as subroutines. They arise naturally in a remarkable number of real-world settings. A limited list includes transportation planning, network optimization, packet routing, image segmentation, speech recognition, document formatting, robotics, compilers, traffic information systems, and dataflow analysis. Shortest path algorithms have been studied since the 1950's and still remain an active area of research. This volume reports on the research carried out by participants during the Ninth DIMACS Implementation Challenge, which led to several improvements of the state of the art in shortest path algorithms. The infrastructure developed during the Challenge facilitated further research in the area, leading to substantial follow-up work as well as to better and more uniform experimental standards. The results of the Challenge included new cutting-edge techniques for emerging applications such as GPS navigation systems, providing experimental evidence of the most effective algorithms in several real-world settings.

149 citations

##### Cited by

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01 Jan 2009

TL;DR: This paper presents a meta-modelling framework for modeling and testing the robustness of the modeled systems and some of the techniques used in this framework have been developed and tested in the field.

Abstract: ing WS1S Systems to Verify Parameterized Networks . . . . . . . . . . . . 188 Kai Baukus, Saddek Bensalem, Yassine Lakhnech and Karsten Stahl FMona: A Tool for Expressing Validation Techniques over Infinite State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 J.-P. Bodeveix and M. Filali Transitive Closures of Regular Relations for Verifying Infinite-State Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220 Bengt Jonsson and Marcus Nilsson Diagnostic and Test Generation Using Static Analysis to Improve Automatic Test Generation . . . . . . . . . . . . . 235 Marius Bozga, Jean-Claude Fernandez and Lucian Ghirvu Efficient Diagnostic Generation for Boolean Equation Systems . . . . . . . . . . . . 251 Radu Mateescu Efficient Model-Checking Compositional State Space Generation with Partial Order Reductions for Asynchronous Communicating Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Jean-Pierre Krimm and Laurent Mounier Checking for CFFD-Preorder with Tester Processes . . . . . . . . . . . . . . . . . . . . . . . 283 Juhana Helovuo and Antti Valmari Fair Bisimulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 Thomas A. Henzinger and Sriram K. Rajamani Integrating Low Level Symmetries into Reachability Analysis . . . . . . . . . . . . . 315 Karsten Schmidt Model-Checking Tools Model Checking Support for the ASM High-Level Language . . . . . . . . . . . . . . 331 Giuseppe Del Castillo and Kirsten Winter Table of

1,687 citations

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27 Aug 2007TL;DR: Ethane allows managers to define a single network-wide fine-grain policy, and then enforces it directly, and this design is backwards-compatible with existing hosts and switches.

Abstract: This paper presents Ethane, a new network architecture for the enterprise. Ethane allows managers to define a single network-wide fine-grain policy, and then enforces it directly. Ethane couples extremely simple flow-based Ethernet switches with a centralized controller that manages the admittance and routing of flows. While radical, this design is backwards-compatible with existing hosts and switches.We have implemented Ethane in both hardware and software, supporting both wired and wireless hosts. Our operational Ethane network has supported over 300 hosts for the past four months in a large university network, and this deployment experience has significantly affected Ethane's design.

1,079 citations

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University of Freiburg

^{1}, Apple Inc.^{2}, Amazon.com^{3}, Martin Luther University of Halle-Wittenberg^{4}, Microsoft^{5}, Karlsruhe Institute of Technology^{6}TL;DR: In this article, the authors survey recent advances in algorithms for route planning in transportation networks, and show that one can compute driving directions in milliseconds or less even at continental scale for road networks, while others can deal efficiently with real-time traffic.

Abstract: We survey recent advances in algorithms for route planning in transportation networks. For road networks, we show that one can compute driving directions in milliseconds or less even at continental scale. A variety of techniques provide different trade-offs between preprocessing effort, space requirements, and query time. Some algorithms can answer queries in a fraction of a microsecond, while others can deal efficiently with real-time traffic. Journey planning on public transportation systems, although conceptually similar, is a significantly harder problem due to its inherent time-dependent and multicriteria nature. Although exact algorithms are fast enough for interactive queries on metropolitan transit systems, dealing with continent-sized instances requires simplifications or heavy preprocessing. The multimodal route planning problem, which seeks journeys combining schedule-based transportation (buses, trains) with unrestricted modes (walking, driving), is even harder, relying on approximate solutions even for metropolitan inputs.

618 citations

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IBM

^{1}TL;DR: This work defines time graphs to extend the traditional notion of an evolving directed graph, capturing link creation as a point phenomenon in time, and develops definitions and algorithms for time-dense community tracking, to crystallize the notion of community evolution.

Abstract: We propose two new tools to address the evolution of hyperlinked corpora. First, we define time graphs to extend the traditional notion of an evolving directed graph, capturing link creation as a point phenomenon in time. Second, we develop definitions and algorithms for time-dense community tracking, to crystallize the notion of community evolution. We develop these tools in the context of Blogspace , the space of weblogs (or blogs). Our study involves approximately 750K links among 25K blogs. We create a time graph on these blogs by an automatic analysis of their internal time stamps. We then study the evolution of connected component structure and microscopic community structure in this time graph. We show that Blogspace underwent a transition behavior around the end of 2001, and has been rapidly expanding over the past year, not just in metrics of scale, but also in metrics of community structure and connectedness. This expansion shows no sign of abating, although measures of connectedness must plateau within two years. By randomizing link destinations in Blogspace, but retaining sources and timestamps, we introduce a concept of randomized Blogspace . Herein, we observe similar evolution of a giant component, but no corresponding increase in community structure. Having demonstrated the formation of micro-communities over time, we then turn to the ongoing activity within active communities. We extend recent work of Kleinberg [11] to discover dense periods of "bursty" intra-community link creation.

616 citations