ppxscal/embedding_network huggingface dataset:
Free Bits, PCPs, and Nonapproximability---Towards Tight Results
Authors: Mihir Bellare, Oded Goldreich, Madhu Sudan
Venue: SIAM Journal on Computing (1998)

This paper continues the investigation of the connection between probabilistically checkable proofs (PCPs) and the approximability of NP-optimization problems. The emphasis is on proving tight nonapproximability results via consideration of measures such as the "free-bit complexity" and the "amortized free-bit complexity" of proof systems.The first part of the paper presents a collection of new proof systems based on a new error-correcting code called the long code. We provide a proof system that has amortized free-bit complexity of $2 + \epsilon$, implying that approximating MaxClique within $N^{\frac13-\e}$, and approximating the Chromatic Number within $N^{\frac15-\e}$, are hard, assuming $\NP\neq\coRP$, for any e > 0. We also derive the first explicit and reasonable constant hardness factors for Min Vertex Cover, $\MSAT{2}$, and Max Cut, and we improve the hardness factor for $\MSAT{3}$. We note that our nonapproximability factors for $\maxsnp$ problems are appreciably close to the values known to be achievable by polynomial-time algorithms. Finally, we note a general approach to the derivation of strong nonapproximability results under which the problem reduces to the construction of certain "gadgets."The increasing strength of nonapproximability results obtained via the PCP connection motivates us to ask how far this can go and whether PCPs are inherent in any way. The second part of the paper addresses this. The main result is a "reversal" of the connection due to Feige et al. (FGLSS connection) [J. ACM, 43 (1996), pp. 268--292]: where the latter had shown how to translate proof systems for NP into NP-hardness of approximation results for MaxClique, we show how any NP-hardness of approximation result for MaxClique yields a proof system for NP. Roughly, our result says that for any constant f, if MaxClique is NP-hard to approximate within N 1(1+f), then $\NP\subseteq \overline{\fpcp}[\log,f]$, the latter being the class of languages possessing proofs of logarithmic randomness and amortized free-bit complexity f. This suggests that PCPs are inherent to obtaining nonapproximability results. Furthermore, the tight relation suggests that reducing the amortized free-bit complexity is necessary for improving the nonapproximability results for MaxClique.The third part of our paper initiates a systematic investigation of the properties of PCP and FPCP (free PCP) as a function of the following various parameters: randomness, query complexity, free-bit complexity, amortized free-bit complexity, proof size, etc. We are particularly interested in triviality results, which indicate which classes are not powerful enough to capture NP. We also distill the role of randomized reductions in this area and provide a variety of useful transformations between proof checking complexity classes.
Convex Set Symmetry Measurement via Minkowski Addition
Authors: A. V. Tuzikov, G. L. Margolin, A. I. Grenov
Venue: Journal of Mathematical Imaging and Vision (1997)

We introduce and investigate measures of rotation and reflection symmetries for compact convex sets. The appropriate symmetrization transformations are used to transform original sets into symmetrical ones. Symmetry measures are defined as the ratio of volumes (Lebesgue measure) of the original set and the corresponding symmetrical set.For the case of rotation symmetry we use as a symmetrization transformation a generalization of the Minkowski symmetric set (a difference body) for a cyclic group of rotations. For the case of reflection symmetry we investigate Blaschke symmetrization. Given a convex set and a hyperplane E in R^n we get a set symmetrical with respect to this hyperplane. Analyzing all hyperplanes containing the coordinate center one gets the measure of reflection symmetry. We discuss the lower bounds of this symmetry measure and also a derived symmetry measure.In the two dimensional case a perimetric measure representation of convex sets is applied for convex sets symmetrization as well as for the symmetry measure calculation. The perimetric measure allows also to perform a decomposition of a compact convex set into Minkowski sum of two sets. The first one is rotationally symmetrical and the second one is completely asymmetrical in the sense that it does not allow such a decomposition.We discuss a problem of the fast computation of symmetrization transformations. Minkowski addition of two sets is reduced to the convolution of their characteristic functions. Therefore, in the case of the discrete plane Z^2, Fast Fourier Transformation can be applied for the fast computation of symmetrization transformations.
A type based sharing analysis for update avoidance and optimisation
Authors: Jörgen Gustavsson
Venue: Proceedings of the third ACM SIGPLAN international conference on Functional programming (1998)

Sharing of evaluation is crucial for the efficiency of lazy functional languages, but unfortunately the machinery to implement it carries an inherent overhead. In abstract machines this overhead shows up as the cost of performing updates, many of them actually unnecessary, and also in the cost of the associated bookkeeping, that is keeping track of when and where to update. In spineless abstract machines, such as the STG-machine and the TIM, this bookkeeping consists of pushing, checking for and popping update markers. Checking for update markers is a very frequent operation and indeed the implementation of the STG-machine has been optimised for fast update marker checks at the expense of making the pushing and popping of update markers more costly.In this paper we present a type based sharing analysis that can determine when updates can be safely omitted and marker checks bypassed. The type system is proved sound with respect to the lazy Krivine machine. We have implemented the analysis and the preliminary benchmarks seem very promising. Most notably, virtually all update marker checks can be avoided. This may make the tradeoffs of current implementations obsolete and calls for new abstract machine designs.
Using channel state dependent packet scheduling to improve TCP throughput over wireless LANs
Authors: Pravin Bhagwat, Partha Bhattacharya, Arvind Krishma, Satish K. Tripathi
Venue: Wireless Networks (1997)

In recent years, a variety of mobile computers equipped with wireless communication devices have become popular. These computers use applications and protocols, originally developed for wired desktop hosts, to communicate over wireless channels. Unlike wired networks, packets transmitted on wireless channels are often subject to burst errors which cause back to back packet losses. In this paper we study the effect of burst packet errors and error recovery mechanisms employed in wireless MAC protocols on the performance of transport protocols such as TCP. Most wireless LAN link layer protocols recover from packet losses by retransmitting lost segments. When the wireless channel is in a burst error state, most retransmission attempts fail, thereby causing poor utilization of the wireless channel. Furthermore, in the event of multiple sessions sharing a wireless link, FIFO packet scheduling can cause the HOL blocking effect, resulting in unfair sharing of the bandwidth. This observation leads to a new class of packet dispatching methods which explicitly take wireless channel characteristics into consideration in making packet dispatching decisions. We compare a variety of channel state dependent packet (CSDP) scheduling methods with a view towards enhancing the performance of transport layer sessions. Our results indicate that by employing a CSDP scheduler at the wireless LAN device driver level, significant improvement in channel utilization can be achieved in typical wireless LAN configurations.
How Easy is Matching 2D Line Models Using Local Search?
Authors: J. Ross Beveridge, Edward M. Riseman
Venue: IEEE Transactions on Pattern Analysis and Machine Intelligence (1997)

Local search is a well established and highly effective method for solving complex combinatorial optimization problems. Here, local search is adapted to solve difficult geometric matching problems. Matching is posed as the problem of finding the optimal many-to-many correspondence mapping between a line segment model and image line segments. Image data is assumed to be fragmented, noisy, and cluttered. The algorithms presented have been used for robot navigation, photo interpretation, and scene understanding. This paper explores how local search performs as model complexity increases, image clutter increases, and additional model instances are added to the image data. Expected run-times to find optimal matches with 95 percent confidence are determined for 48 distinct problems involving six models. Nonlinear regression is used to estimate run-time growth as a function of problem size. Both polynomial and exponential growth models are fit to the run-time data. For problems with random clutter, the polynomial model fits better and growth is comparable to that for tree search. For problems involving symmetric models and multiple model instances, where tree search is exponential, the polynomial growth model is superior to the exponential growth model for one search algorithm and comparable for another.
Metaheuristics for High School Timetabling
Authors: Alberto Colorni, Marco Dorigo, Vittorio Maniezzo
Venue: Computational Optimization and Applications (1998)

In this paper we present the results of an investigation of the possibilities offered by three well-known metaheuristic algorithms to solve the timetable problem, a multi-constrained, NP-hard, combinatorial optimization problem with real-world applications. First, we present our model of the problem, including the definition of a hierarchical structure for the objective function, and of the neighborhood search operators which we apply to matrices representing timetables. Then we report about the outcomes of the utilization of the implemented systems to the specific case of the generation of a school timetable. We compare the results obtained by simu lated annealing, tabu search and two versions, with and without local search, of the genetic algorithm. Our results show that GA with local search and tabu search based on temporary problem relaxations both outperform simulated annealing and handmade timetables.
Efficient Algorithms for Data Distribution on Distributed Memory Parallel Computers
Authors: PeiZong Lee
Venue: IEEE Transactions on Parallel and Distributed Systems (1997)

Data distribution has been one of the most important research topics in parallelizing compilers for distributed memory parallel computers. Good data distribution schema should consider both the computation load balance and the communication overhead. In this paper, we show that data redistribution is necessary for executing a sequence of Do-loops if the communication cost due to performing this sequence of Do-loops is larger than a threshold value. Based on this observation, we can prune the searching space and derive efficient dynamic programming algorithms for determining effective data distribution schema to execute a sequence of Do-loops with a general structure. Experimental studies on a 32-node nCUBE-2 computer are also presented.
New email security infrastructure
Authors: Martin Ferris
Venue: Proceedings of the 1994 workshop on New security paradigms (1994)

This paper addresses the problem of analysing an information system for security flaws or vulnerabilities in a way that is analogous to the analysis of a safety-critical system. In particular, instead of adopting the approach that security is a property that must be proved to hold (fault avoidance), it shows how to analyse a system for possible security failures so that fault prevention, tolerance, recovery or even fault acceptance techniques can be chosen where appropriate.
Operating system benchmarking in the wake of lmbench: a case study of the performance of NetBSD on the Intel x86 architecture
Authors: Aaron B. Brown, Margo I. Seltzer
Venue: ACM SIGMETRICS Performance Evaluation Review (1997)

The lmbench suite of operating system microbenchmarks provides a set of portable programs for use in cross-platform comparisons. We have augmented the lmbench suite to increase its flexibility and precision, and to improve its methodological and statistical operation. This enables the detailed study of interactions between the operating system and the hardware architecture. We describe modifications to lmbench, and then use our new benchmark suite, hbench:OS, to examine how the performance of operating system primitives under NetBSD has scaled with the processor evolution of the Intel x86 architecture. Our analysis shows that off-chip memory system design continues to influence operating system performance in a significant way and that key design decisions (such as suboptimal choices of DRAM and cache technology, and memory-bus and cache coherency protocols) can essentially nullify the performance benefits of the aggressive execution core and sophisticated on-chip memory system of a modern processor such as the Intel Pentium Pro.
Counting Problems Associated With Steiner Trees In Graphs
Authors: J. Scott Provan, Manoj K. Chari
Venue: SIAM Journal on Discrete Mathematics (1997)

This paper considers counting problems associated with K-spanning and K-disconnecting sets for a specified terminal set K in an undirected graph G. In particular, we consider the problems of computing the number of Steiner trees and min K-cuts for G, as well as K-spanning and K-disconnecting sets of cardinality close to the minimum values. Among other things, these numbers are critical to the efficient approximation of K-connected reliability measures in stochastic networks. Although the counting problems considered in this paper are NP-hard in general, a large number of methods for finding shortest paths, min cuts, and Steiner trees in graphs can be extended to efficiently count K-spanning and K-disconnecting sets in important special cases.
Global interconnect sizing and spacing with consideration of coupling capacitance
Authors: Jason Cong, Lei He, Cheng-Kok Koh, Zhigang Pan
Venue: Proceedings of the 1997 IEEE/ACM international conference on Computer-aided design (1997)

The paper presents an efficient approach to perform global interconnect sizing and spacing (GISS) for multiple nets to minimize interconnect delays with consideration of coupling capacitance, in addition to area and fringing capacitances. We introduce the formulation of symmetric and asymmetric wire sizing and spacing. We prove two important results on the symmetric and asymmetric effective fringing properties which lead to a very effective bound computation algorithm to compute the upper and lower bounds of the optimal wire sizing and spacing solution for all nets under consideration. Our experiments show that in most cases the upper and lower bounds meet quickly after a few iterations and we actually obtain the optimal solution. To our knowledge, this is the first in depth study of global wire sizing and spacing for multiple nets with consideration of coupling capacitance. Experimental results show that our GISS solutions lead to substantially better delay reduction than existing single net wire sizing solutions without consideration of coupling capacitance.
Interprocedural control flow analysis of first-order programs with tail-call optimization
Authors: Saumya K. Debray, Todd A. Proebsting
Venue: ACM Transactions on Programming Languages and Systems (TOPLAS) (1997)

Knowledge of low-level control flow is essential for many compiler optimizations. In systems with tail-call optimization, the determination of interprocedural control flow is complicated by the fact that because of tail-call optimization, control flow at procedure returns is not readily evident from the call graph of the program. This article shows how interprocedural control-flow analysis of first-order programs can be carried out using well-known concepts from parsing theory. In particular, we show that context-insensitive ( or zeroth-order) control-flow analysis corresponds to the notion of FOLLOW sets in context-free grammars, while context-sensitive (or first-order) control-flow analysis corresponds to the notion of LR(1) items. The control-flow information so obtained can be used to improve the precision of interprocedural dataflow analyses as well as to extend certain low-level code optimizations across procedure boundaries.
DAda&mdash;an Ada preprocessor for functional programming
Authors: Paul A. Bailes, Dan Johnson, Eric Salzman, Li Wang
Venue: Proceedings of the conference on TRI-ADA '90 (1990)

The impact of declarative (functional) programming is inhibited by the need to learn/use new languages. A series of language extensions implemented by preprocessing, which integrates functional programming into the Ada culture, is described. Features include lazy streams, recursive data structures, the abolition of assignment and its replacement by data-flow control constructs.
A hardware/software partitioner using a dynamically determined granularity
Authors: Jörg Henkel, Rolf Ernst
Venue: Proceedings of the 34th annual Design Automation Conference (1997)

Computer aided hardware/software partitioning is one of the keychallenges in hardware/software co-design. While previous approacheshave used a fixed granularity, i.e. the size of the partitioningobjects was fixed, we present a partitioning approach thatdynamically determines the partitioning granularity to adapt optimizationsteps to application properties and to intermediate optimizationresults. Experiments with simulated annealing optimizationshow a faster convergence and far better adaptability to costfunction variations than in previous experiments with fixed granularity.
A distributed numerical/simulative algorithm for the analysis of large continuous time Markov chains
Authors: Peter Buchholz
Venue: Proceedings of the eleventh workshop on Parallel and distributed simulation (1997)

A distributed algorithm is introduced for the analysis of large continuous time Markov chains (CTMCs) by combining in some sense numerical solution techniques and simulation. CTMCs are described as a set of processes communicating via message passing. The state of a process is described by a probability distribution over a set of reachable states rather than by a single state. Simulation is used to determine event times and messages types to be exchanged, whereas transitions are realized by vector matrix products as in iterative numerical analysis techniques. In this way, the state space explosion of numerical analysis is avoided, but it is still possible to determine more detailed results than with simulation. Parallelization of the algorithm is realized applying a conservative synchronization scheme, which exploits the possibility of precomputing event times as already proposed for parallel simulation of CTMCs. In contrast to a pure simulation approach, the amount of computation is increased, whereas the amount of communication keeps constant. Hence it is possible to achieve even on a workstation cluster a significant speedup.
An introduction to the Beetle Forth virtual processor
Authors: Reuben R. Thomas
Venue: ACM SIGPLAN Notices (1997)

Beetle is a virtual processor designed for the Forth language. It uses a modified, byte-stream code designed for efficient execution which is binary portable between implementations. It has been implemented in C and assembler. The C implementation is completely machine independent with the exception of interactive input and output; the assembler version runs the supplied Forth compiler at up to half the speed of the corresponding native code compiler and generates more compact code. Beetle is designed to be embedded in other programs; a simple debugger has been written to demonstrate this ability. Beetle can be configured to perform bounds checking on all memory references. A standard library is implemented; access to native code routines is also possible, allowing Forth and C programs to call each other.
Assuring security and privacy for digital library transactions on the Web: client and server security policies
Authors: Marianne Winslett, Neil Ching, Vicki Jones, Igor Slepchin
Venue: Proceedings of the IEEE international forum on Research and technology advances in digital libraries (1997)

Often an information source on the Web would like to provide different classes of service to different clients. In the autonomous, highly distributed world of the Web, the traditional approach of using authentication to differentiate between classes of clients is no longer sufficient, as knowledge of a client's identity will often not suffice to determine whether a client is authorized to use a service. In [CJW96] we proposed the use of digital credentials to help solve this problem; but their use will in turn introduce a bevy of new problems associated with credential management. In this paper we propose the use of server security policies to aid in the management of a client's digital credentials. We propose a structure for such policies, and briefly describe an implementation of personal security assistants and server security assistants that embodies our proposed approach.
Matching Sets of 3D Line Segments with Application to Polygonal Arc Matching
Authors: Behzad Kamgar-Parsi, Behrooz Kamgar-Parsi
Venue: IEEE Transactions on Pattern Analysis and Machine Intelligence (1997)

In this paper, we consider two sets of corresponding 3D line segments of equal length. We derive a closed-form solution for the coordinate transform (rotation and translation) that gives the best match between the two sets; best in the sense of a least-squares distance measure between the sets. We use these results as the basis to construct efficient algorithms for solving other problems in computer vision. Specifically, we address the problem of matching polygonal arcs, that is, the problem of finding a match between a short arc and a piece of a long arc.
Representation of 3D Surfaces by Two-Variable Fourier Descriptors
Authors: Ming-Fang Wu, Hsin-Teng Sheu
Venue: IEEE Transactions on Pattern Analysis and Machine Intelligence (1998)

A method for generating two-variable 3D FDs directly from a striped lighting system is developed. An iterative algorithm is proposed to compute the two-variable 3D FDs for both axisymmetric and nonaxisymmetric objects and a formula for convergence test is derived. Experiments conducted for a set of 3D objects show that the iterative algorithm converges very quickly and the two-variable 3D FD representations are attained accurately.
Some subjective validation methods using graphical displays of data
Authors: Robert G. Sargent
Venue: Proceedings of the 28th conference on Winter simulation (1996)

Subjective methods for operational validity are presented that use graphical displays of histograms, box plots, and behavior graphs. These methods allow the data to be correlated, have any statistical distribution, and be limited in the number of observations. Model data are used for the reference distribution (instead of a theoretical distribution such as the t or F) and for reference to compare the system data against. These methods are very general and can be used in validating different types of models.
Maximum independent sets on transitive graphs and their applications in testing and CAD
Authors: Dimitrios Kagaris, Spyros Tragoudas
Venue: Proceedings of the 1997 IEEE/ACM international conference on Computer-aided design (1997)

We present a polynomial time algorithm that finds the maximum weighted independent set of a transitive graph. The studied problem finds applications in a variety of VLSI contexts, including path delay fault testing, scheduling in high level synthesis and channel routing in physical design automation. The algorithm has been implemented and incorporated in a CAD tool for path delay fault testing. We experimentally verify its impact in the latter context.