Cost-Sharing Mechanisms for Network Design

We consider a single-source network design problem from a game-theoretic perspective. Gupta, Kumar and Roughgarden (Proc. 35th Annual ACM STOC, pp. 365–372, 2003) developed a simple method for a single-source rent-or-buy problem that also yields the best-known approximation ratio for the problem. We show how to use a variant of this method to develop an approximately budget-balanced and group strategyproof cost-sharing method for the problem. The novelty of our approach stems from our obtaining the cost-sharing methods for the rent-or-buy problem by carefully combining cost-shares for the simpler Steiner tree problem. Our algorithm is conceptually simpler than the previous such cost-sharing method due to Pál and Tardos (Proc. 44th Annual FOCS, pp. 584–593, 2003), and improves the previously-known approximation factor of 15 to 4.6. A preliminary version of this work appears in the Proc. International Workshop on Approximation Algorithms for Combinatorial Optimization Problems, 2004. This research was done in part during the IMA Workshop on Network Management and Design at the University of Minnesota, April 2003. A. Gupta supported in part by an NSF CAREER award CCF-0448095, and by an Alfred P. Sloan Fellowship. A. Srinivasan supported in part by the National Science Foundation under Grant No. 0208005 and ITR Award CNS-0426683. Research of é. Tardos supported in part by ONR grant N00014-98-1-0589, and NSF grants CCR-0311333 and CCR-0325453.     

A Fair, Secure and Trustworthy Peer-to-Peer Based Cycle-Sharing System

The increased popularity of Grid systems and cycle sharing across organizations requires scalable systems that provide facilities to locate resources, to be fair in the use of those resources, to allow resource providers to host untrusted applications safely, and to allow resource consumers to monitor the progress and correctness of jobs executing on remote machines. This paper presents such a framework that locates computational resources with a peer-to-peer network, assures fair resource usage with a distributed credit accounting system, provides resource contributors a safe environment, for example Java Virtual Machine (JVM), to host untrusted applications, and provides the resource consumers a monitoring system, GridCop, to track the progress and correctness of remotely executing jobs. We present the details of the credit accounting subsystem and the GridCop remote job monitoring subsystem. GridCop and the distributed credit accounting system together enable incremental payments so that the risk for both resource providers and resource consumers is bounded.*This work was supported by NSF CAREER award grant ACI-0238379 and NSF grants CCR-0313026 and CCR-0313033.     

Distributed reconfiguration of metamorphic robot chains

The problem we address is the distributed reconfiguration of a planar metamorphic robotic system composed of any number of hexagonal modules. After presenting a framework for classifying motion planning algorithms for metamorphic robotic systems, we describe distributed algorithms for reconfiguring a straight chain of hexagonal modules to any intersecting straight chain configuration. We prove our algorithms are correct, and show that they are either optimal or asymptotically optimal in the number of moves and asymptotically optimal in the time required for parallel reconfiguration.Received: 28 October 2002, Accepted: 31 October 2003, Published online: 1 March 2004 Corresdpondence to: Jennifer E. WalterNancy M. Amato: amato]@cs.tamu.edu A preliminary version of this paper appeared in the Proc. of the 19th ACM Symposium on Principles of Distributed Computing, July 2000, pages 171-180. The work of N. Amato and J. Walter was supported in part by NSF CAREER Award CCR-9624315, NSF Grants IIS-9619850, ACI-9872126, EIA-9975018, EIA-0103742, EIA-9805823, ACR-0081510, ACR-0113971, CCR-0113974, EIA-9810937, EIA-0079874, by the Texas Higher Education Coordinating Board grant ARP-036327-017, and by the DOE ASCI ASAP program grant B347886. The work of J. Walter was supported in part by Department of Education GAANN and GE Faculty of the Future fellowships.     

Can PAC learning algorithms tolerate random attribute noise?

This paper studies the robustness of PAC learning algorithms when the instance space is {0,1}ⁿ, and the examples are corrupted by purely random noise affecting only the attributes (and not the labels). Foruniform attribute noise, in which each attribute is flipped independently at random with the same probability, we present an algorithm that PAC learns monomials for any (unknown) noise rate less than ₂ ¹ . Contrasting this positive result, we show thatproduct random attribute noise, where each attributei is flipped randomly and independently with its own probability p_i, is nearly as harmful as malicious noise-no algorithm can tolerate more than a very small amount of such noise.The research of S. A. Goldman was supported in part by a GE Foundation Junior Faculty grant and NSF Grant CCR-9110108. Part of this research was conducted while the author was at the M.I.T. Laboratory for Computer Science and supported by NSF Grant DCR-8607494 and a grant from the Siemens Corporation. The research of R. H. Sloan was supported in part by NSF Grant CCR-9108753. Part of this research was conducted while the author was at Harvard and supported by ARO Grant DAAL 03-86-K-0171.     

Service selection algorithms for Web services with end-to-end QoS constraints

Web services are new forms of Internet software that can be universally deployed and invoked using standard protocols. Services from different providers can be integrated into a composite service regardless of their locations, platforms, and/or execution speeds to implement complex business processes and transactions. In this paper, we study the end-to-end QoS issues of composite services by utilizing a QoS broker that is responsible for selecting and coordinating the individual service component. We design the service selection algorithms used by QoS brokers to construct the optimal composite service. The objective of the algorithms is to maximize the user-defined utility function value while meeting the end-to-end delay constraint. We propose two solution approaches to the service selection problem: the combinatorial approach, by modeling the problem as the Multiple Choice Knapsack Problem (MCKP), and the graph approach, by modeling the problem as the constrained shortest path problem in the graph theory. We study efficient solutions for each approach.This research was supported in part by NSF CCR-9901697.     

Learning Binary Relations Using Weighted Majority Voting

In this paper we demonstrate how weighted majority voting with multiplicative weight updating can be applied to obtain robust algorithms for learning binary relations. We first present an algorithm that obtains a nearly optimal mistake bound but at the expense of using exponential computation to make each prediction. However, the time complexity of our algorithm is significantly reduced from that of previously known algorithms that have comparable mistake bounds. The second algorithm we present is a polynomial time algorithm with a non-optimal mistake bound. Again the mistake bound of our second algorithm is significantly better than previous bounds proven for polynomial time algorithms.A key contribution of our work is that we define a non-pure or noisy binary relation and then by exploiting the robustness of weighted majority voting with respect to noise, we show that both of our algorithms can learn non-pure relations. These provide the first algorithms that can learn non-pure binary relations.The first author was supported in part by NSF grant CCR-91110108 and NSF National Young Investigator Grant CCR-9357707 with matching funds provided by Xerox Corporation, Palo Alto Research Center and WUTA. The second author was supported by ONR grant NO0014-91-J-1162 and NSF grant IRI-9123692.     

Constructing invariants for hybrid systems

We present a new method for generating algebraic invariants of hybrid systems. The method reduces the invariant generation problem to a constraint solving problem using techniques from the theory of ideals over polynomial rings. Starting with a template invariant—a polynomial equality over the system variables with unknown coefficients—constraints are generated on the coefficients guaranteeing that the solutions are inductive invariants. To control the complexity of the constraint solving, several stronger conditions that imply inductiveness are proposed, thus allowing a trade-off between the complexity of the invariant generation process and the strength of the resulting invariants. This research was supported in part by NSF grants CCR-01-21403, CCR-02-20134 and CCR-02-09237, by ARO grant DAAD19-01-1-0723, by ARPA/AF contracts F33615-00-C-1693 and F33615-99-C-3014, and by NAVY/ONR contract N00014-03-1-0939.     

Symmetry and model checking

We show how to exploit symmetry in model checking for concurrent systems containing many identical or isomorphic components. We focus in particular on those composed of many isomorphic processes. In many cases we are able to obtain significant, even exponential, savings in the complexity of model checking.The author's work was supported in part by NSF Grant CCR 941-5496, Semiconductor Research Corporation Contract 95-DP-388, and Texas Advanced Technology Program Grant 003658-250.The author's work was supported in part by NSF Grant CCR-9212183.     

Mechanism design for policy routing

The Border Gateway Protocol (BGP) for interdomain routing is designed to allow autonomous systems (ASes) to express policy preferences over alternative routes. We model these preferences as arising from an AS’s underlying utility for each route and study the problem of finding a set of routes that maximizes the overall welfare (ie, the sum of all ASes’ utilities for their selected routes). We show that, if the utility functions are unrestricted, this problem is NP-hard even to approximate closely. We then study a natural class of restricted utilities that we call next-hop preferences. We present a strategyproof, polynomial-time computable mechanism for welfare-maximizing routing over this restricted domain. However, we show that, in contrast to earlier work on lowest-cost routing mechanism design, this mechanism appears to be incompatible with BGP and hence difficult to implement in the context of the current Internet. Our contributions include a new complexity measure for Internet algorithms, dynamic stability, which may be useful in other problem domains. Supported in part by ONR grant N00014-01-1-0795 and NSF grantITR-0219018.Supported by ONR grant N00014-01-1-0795 and NSF grant ITR-0219018. Most of this work was done while the author was at Yale University. Supported in part by NSF grants ITR-0121555 and ANI-0207399. This work was supported by the DoD University Research Initiative (URI) program administered by the Office of Naval Research under Grant N00014-01-1-0795. It was presented in preliminary form at the 2004 ACM Symposium on Principles of Distributed Computing [7]. Portions of this work appeared in preliminary form in the second author’s PhD Thesis [16].     

Scheduling on Unrelated Machines under Tree-Like Precedence Constraints

We present polylogarithmic approximations for the R|prec|C _max and R|prec|∑ _j w _j C _j problems, when the precedence constraints are “treelike”—i.e., when the undirected graph underlying the precedences is a forest. These are the first non-trivial generalizations of the job shop scheduling problem to scheduling with precedence constraints that are not just chains. These are also the first non-trivial results for the weighted completion time objective on unrelated machines with precedence constraints of any kind. We obtain improved bounds for the weighted completion time and flow time for the case of chains with restricted assignment—this generalizes the job shop problem to these objective functions. We use the same lower bound of “congestion + dilation”, as in other job shop scheduling approaches (e.g. Shmoys, Stein and Wein, SIAM J. Comput. 23, 617–632, 1994). The first step in our algorithm for the R|prec|C _max problem with treelike precedences involves using the algorithm of Lenstra, Shmoys and Tardos to obtain a processor assignment with the congestion + dilation value within a constant factor of the optimal. We then show how to generalize the random-delays technique of Leighton, Maggs and Rao to the case of trees. For the special case of chains, we show a dependent rounding technique which leads to a bicriteria approximation algorithm for minimizing the flow time, a notoriously hard objective function. A preliminary version of this paper appeared in the Proc. International Workshop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX), pages 146–157, 2005. V.S. Anil Kumar supported in part by NSF Award CNS-0626964. Part of this work was done while at the Los Alamos National Laboratory, and supported in part by the Department of Energy under Contract W-7405-ENG-36. M.V. Marathe supported in part by NSF Award CNS-0626964. Part of this work was done while at the Los Alamos National Laboratory, and supported in part by the Department of Energy under Contract W-7405-ENG-36. Part of this work by S. Parthasarathy was done while at the Department of Computer Science, University of Maryland, College Park, MD 20742, and in part while visiting the Los Alamos National Laboratory. Research supported in part by NSF Award CCR-0208005 and NSF ITR Award CNS-0426683. Research of A. Srinivasan supported in part by NSF Award CCR-0208005, NSF ITR Award CNS-0426683, and NSF Award CNS-0626636.     

A BGP-based mechanism for lowest-cost routing

The routing of traffic between Internet domains, or Autonomous Systems (ASs), a task known as interdomain routing, is currently handled by the Border Gateway Protocol (BGP). In this paper, we address the problem of interdomain routing from a mechanism-design point of view. The application of mechanism-design principles to the study of routing is the subject of earlier work by Nisan and Ronen [16] and Hershberger and Suri [12]. In this paper, we formulate and solve a version of the routing-mechanism design problem that is different from the previously studied version in three ways that make it more accurately reflective of real-world interdomain routing: (1) we treat the nodes as strategic agents, rather than the links; (2) our mechanism computes lowest-cost routes for all sourcedestination pairs and payments for transit nodes on all of the routes (rather than computing routes and payments for only one sourcedestination pair at a time, as is done in [12,16]); (3) we show how to compute our mechanism with a distributed algorithm that is a straightforward extension to BGP and causes only modest increases in routing-table size and convergence time (in contrast with the centralized algorithms used in [12,16]). This approach of using an existing protocol as a substrate for distributed computation may prove useful in future development of Internet algorithms generally, not only for routing or pricing problems. Our design and analysis of a strategyproof, BGP-based routing mechanism provides a new, promising direction in distributed algorithmic mechanism design, which has heretofore been focused mainly on multicast cost sharing. Supported in part by ONR grants N00014-01-1-0795 and N00014-01-1-0447 and NSF grant CCR-0105337. Supported in part by NSF grants ITR-0081698 and ITR-0121555 and by an IBM Faculty Development Award. Supported by ONR grant N00014-01-1-0795. Supported in part by NSF grants ITR-0205519, ANI-0207399, ITR-0121555, ITR-0081698, ITR-0225660, and ANI-0196514. This work was supported by the DoD University Research Initiative (URI) program administered by the Office of Naval Research under Grant N00014-01-1-0795. It was presented in preliminary form at the 2002 ACM Symposium on Principles of Distributed Computing [5].     

VLISP: A verified implementation of Scheme

The VLISP project showed how to produce a comprehensively verified implementation for a programming language, namely Scheme. This paper introduces two more detailed studies on VLISP [13, 21]. It summarizes the basic techniques that were used repeatedly throughout the effort. It presents scientific conclusions about the applicability of the these techniques as well as engineering conclusions about the crucial choices that allowed the verification to succeed.The work reported here was carried out as part of The MITRE Corporation's Technology Program, under funding from Rome Laboratory, Electronic Systems Command, United States Air Force, through contract F19628-89-C-0001. Preparation of this paper was generously supported by The MITRE Corporation. Mitchell Wand's participation was partly supported by NSF and DARPA under NSF grants CCR-9002253 and CCR-9014603.     

Pricing Internet services: proposed improvements

Flat-rate pricing appeals to Internet users and service providers because of its simplicity and predictability. However, congestion is the inevitable consequence of flat-rate pricing because Internet users who pay a fixed access fee have no incentive to limit their network usage. Future applications that require timely delivery of data will require mechanisms for allocating network resources that give consumers choices in services and prices while allowing service providers to recover their costs. We examine the proposed improvements in Internet pricing that are designed to increase its economic efficiency and support the deployment of new applications that require a better quality of service than the Internet currently offers     

An Algorithm for Strongly Connected Component Analysis in n log n Symbolic Steps

We present a symbolic algorithm for strongly connected component decomposition. The algorithm performs Θ(n log n) image and preimage computations in the worst case, where n is the number of nodes in the graph. This is an improvement over the previously known quadratic bound. The algorithm can be used to decide emptiness of Büchi automata with the same complexity bound, improving Emerson and Lei's quadratic bound, and emptiness of Streett automata, with a similar bound in terms of nodes. It also leads to an improved procedure for the generation of nonemptiness witnesses. This work was supported in part by SRC contract 98-DJ-620 and NSF grant CCR-99-71195. This work was done while the author was at the University of Colorado at Boulder.     

A bounded approximation for the minimum cost 2-sat problem

Given a satisfiable Boolean formula in 2-CNF, it is NP-hard to find a satisfying assignment that contains a minimum number of true variables. A polynomial-time approximation algorithm is given that finds an assignment with at most twice as many true variables as necessary. The algorithm also works for a weighted generalization of the problem. An application to the optimal stable roommates problem is given in detail, and other applications are mentioned.D. Gusfield was supported in part by NSF Grant CCR-8803704. Part of this work was done while he was at Yale University, partially supported by NSF Grant MCS-8105894. L. Pitt was supported in part by NSF Grant IRI-8809570. Part of this work was done while he was at Yale University, supported by NSF Grants MCS-8002447, MCS-8116678, and MCS-8204246.     

Information-Theoretic Active Polygons for Unsupervised Texture Segmentation

Curve evolution models used in image segmentation and based on image region information usually utilize simple statistics such as means and variances, hence can not account for higher order nature of the textural characteristics of image regions. In addition, the object delineation by active contour methods, results in a contour representation which still requires a substantial amount of data to be stored for subsequent multimedia applications such as visual information retrieval from databases. Polygonal approximations of the extracted continuous curves are required to reduce the amount of data since polygons are powerful approximators of shapes for use in later recognition stages such as shape matching and coding. The key contribution of this paper is the development of a new active contour model which nicely ties the desirable polygonal representation of an object directly to the image segmentation process. This model can robustly capture texture boundaries by way of higher-order statistics of the data and using an information-theoretic measure and with its nature of the ordinary differential equations. This new variational texture segmentation model, is unsupervised since no prior knowledge on the textural properties of image regions is used. Another contribution in this sequel is a new polygon regularizer algorithm which uses electrostatics principles. This is a global regularizer and is more consistent than a local polygon regularization in preserving local features such as corners.Supported by NSF grant CCR-0133736.Partially supported by AFOSR grant F49620-98-1-0190 and NSF grant CCR-9984067.     

The VLISP verified PreScheme compiler

This paper describes a verified compiler for PreScheme, the implementation language for thevlisp run-time system. The compiler and proof were divided into three parts: A transformational front end that translates source text into a core language, a syntax-directed compiler that translates the core language into a combinator-based tree-manipulation language, and a linearizer that translates combinator code into code for an abstract stored-program machine with linear memory for both data and code. This factorization enabled different proof techniques to be used for the different phases of the compiler, and also allowed the generation of good code. Finally, the whole process was made possible by carefully defining the semantics ofvlisp PreScheme rather than just adopting Scheme's. We believe that the architecture of the compiler and its correctness proof can easily be applied to compilers for languages other than PreScheme.This work was supported by Rome Laboratory of the United States Air Force, contract No. F19628-89-C-0001, through the MITRE Corporation, and by NSF and DARPA under NSF grants CCR-9002253 and CCR-9014603. Author's current address: Department of Computer Science and Engineering, Oregon Graduate Institute, P.O. Box 91000, Portland, OR 97291-1000.The work reported here was supported by Rome Laboratory of the United States Air Force, contract No. F19628-89-C-0001. Preparation of this paper was generously supported by The MITRE Corporation.This work was supported by Rome Laboratory of the United States Air Force, contract No. F19628-89-C-0001, through the MITRE Corporation, and by NSF and DARPA under NSF grants CCR-9002253 and CCR-9014603.     

Parallel decoupled terminal-edge bisection method for 3D mesh generation

We present a practical and stable algorithm for the parallel refinement of tetrahedral meshes. The algorithm is based on the refinement of terminal-edges and associated terminal stars. A terminal-edge is a special edge in the mesh which is the longest edge of every element that shares such an edge, while the elements that share a terminal-edge form a terminal star. We prove that the algorithm is inherently decoupled and thus scalable. Our experimental data show that we have a stable implementation able to deal with hundreds of millions of tetrahedra and whose speed is in between one and two order of magnitude higher from the method and implementation we presented (Rivara et al., Proceedings 13th international meshing roundtable, 2004).Maria-Cecilia Rivara and Carlo Calderon's work was partially supported by Fondecyt 1040713.Andriy Fedorov’s work is supported in part by ITR #ACI-0085969, and NGS #ANI-0203974.Nikos Chrisochoides’s work is supported in part by NSF Career Award #CCR-0049086, ITR #ACI-0085969, NGS #ANI-0203974, and ITR #CNS-0312980.     

GSTE is partitioned model checking

Verifying whether an ω-regular property is satisfied by a finite-state system is a core problem in model checking. Standard techniques build an automaton with the complementary language, compute its product with the system, and then check for emptiness. Generalized symbolic trajectory evaluation (GSTE) has been recently proposed as an alternative approach, extending the computationally efficient symbolic trajectory evaluation (STE) to general ω-regular properties. In this paper, we show that the GSTE algorithms are essentially a partitioned version of standard symbolic model-checking (SMC) algorithms, where the partitioning is driven by the property under verification. We export this technique of property-driven partitioning to SMC and show that it typically does speed up SMC algorithms. A shorter version of this paper has been presented at CAV’04 (R. Sebastiani et al., Lecture Notes in Comput. Sci., vol. 3114, pp. 143–160, 2004). R. Sebastiani supported in part by the CALCULEMUS! IHP-RTN EC project, code HPRN-CT-2000-00102, by a MIUR COFIN02 project, code 2002097822_003, and by a grant from the Intel Corporation. M.Y. Vardi supported in part by NSF grants CCR-9988322, CCR-0124077, CCR-0311326, IIS-9908435, IIS-9978135, EIA-0086264, and ANI-0216467 by BSF grant 9800096, and by a grant from the Intel Corporation.     

Fast,contention-free combining tree barriers for shared-memory multiprocessors

In a previous article,⁽¹⁾ Gupta and Hill introduced anadaptive combining tree algorithm for busy-wait barrier synchronization on shared-memory multiprocessors. The intent of the algorithm was to achieve a barrier in logarithmic time when processes arrive simultaneously, and in constant time after the last arrival when arrival times are skewed. Afuzzy ⁽²⁾ version of the algorithm allows a process to perform useful work between the point at which it notifies other processes of its arrival and the point at which it waits for all other processes to arrive. Unfortunately, adaptive combining tree barriers as originally devised perform a large amount of work at each node of the tree, including the acquisition and release of locks. They also perform an unbounded number of accesses to nonlocal locations, inducing large amounts of memory and interconnect contention. We present new adaptive combining tree barriers that eliminate these problems. We compare the performance of the new algorithms to that of other fast barriers on a 64-node BBN Butterfly 1 multiprocessor, a 35-node BBN TC2000, and a 126-node KSR 1. The results reveal scenarios in which our algorithms outperform all known alternatives, and suggest that both adaptation and the combination of fuzziness with tree-style synchronization will be of increasing importance on future generations of shared-memory multiprocessors. At the University of Rochester, this work was supported in part by NSF Institutional Infrastructure grant number CDA-8822724 and ONR research contract number N00014-92-J-1801 (in conjunction with the ARPA Research in Information Science and Technology—High Performance Computing, Software Science and Technology program, ARPA Order No. 8930). At Rice University, this work was supported in part by NSF Cooperative Agreements CCR-8809615 and CCR-912008.