It is well known that two prover proof systems are a convenient tool for establishing hardness of approximation results. In this paper, we show that two prover proof systems are also convenient starting points for est...
详细信息
It is well known that two prover proof systems are a convenient tool for establishing hardness of approximation results. In this paper, we show that two prover proof systems are also convenient starting points for establishing easiness of approximation results. Our approach combines the Feige-Lovasz (STOC92) semidefinite programming relaxation of one-round two-prover proof systems, together with rounding techniques for the solutions of semidefinite programs, as introduced by Goemans and Williamson (STOC94). As a consequence of our approach, we present improved approximation algorithms for MAX 2SAT and MAX DICUT. The algorithms are guaranteed to deliver solutions within a factor of 0.931 of the optimum for MAX 2SAT and within a factor of 0.859 for MAX DICUT, improving upon the guarantees of 0.878 and 0.796 of Goemans and Williamson (1994).< >
The first part of this paper presents new proof systems and improved non-approximability results. In particular we present a proof system for NP using logarithmic randomness and two amortized free bits, so that Max cl...
详细信息
The first part of this paper presents new proof systems and improved non-approximability results. In particular we present a proof system for NP using logarithmic randomness and two amortized free bits, so that Max clique is hard within N/sup 1/3/ and chromatic number within N/sup 1/5/. We also show hardness of 38/37 for Max-3-SAT, 27/26 for vertex cover, 82/81 for Max-cut, and 94/93 for Max-2-SAT. The second part of this paper presents a "reverse" of the FGLSS connection by showing that an NP-hardness result for the approximation of Max clique to within a factor of N/sup 1/(g+1/) would imply a probabilistic verifier for NP with logarithmic randomness and amortized free-bit complexity g. We also show that "existing techniques" won't yield proof systems of less than two bits in amortized free bit complexity. Finally, we initiate a comprehensive study of PCP and FPCP parameters, proving several triviality results and providing several useful transformations.
We introduce new theoretical measures for the qualitative and quantitative assessment of encryption schemes designed for broadcast transmissions. The goal is to allow a central broadcast site to broadcast secure trans...
详细信息
We introduce a formal framework to study the time and space complexity of computing with faulty memory. For the fault-free case, time and space complexities were studied using the "pebbling game" model. We e...
详细信息
Presents a method for the localization and interpretation of modeled objects that is general enough to cover articulated and other types of constrained models. The flexibility between components of the model are expre...
详细信息
Presents a method for the localization and interpretation of modeled objects that is general enough to cover articulated and other types of constrained models. The flexibility between components of the model are expressed as spatial constraints which are fused into the pose estimation during the interpretation process. The constraint fusion assists in obtaining a precise and stable pose of each object's component and in finding the correct interpretation. The proposed method can handle any constraint (including inequalities) between any number of different components of the model. The framework is based on Kalman filtering.< >
A method is presented to correct an approximate polygonal sketch of an image object boundary by adjusting the location of each corner point in the sketch. The method is suitable for the segmentation of unknown images ...
详细信息
A method is presented to correct an approximate polygonal sketch of an image object boundary by adjusting the location of each corner point in the sketch. The method is suitable for the segmentation of unknown images using interactive techniques, and for locating object boundaries in model-based segmentation. For each point, p, at which two lines meet in an open or closed polygonal sketch, a corner segmentation model is derived based on the angle, orientation and scale of the corner defined, and the image function f(x, y) in the immediate region about p. A corner template is then constructed and matched in a small neighborhood about p, thereby providing a corrected polygonal sketch. The segmentation model is correct in 95% of the cases, and the corner is accurately located.< >
暂无评论