18253568
Additive Fluents
An "additive" fluent is a fluent with numerical values such that the effect of several concurrently executed actions on it can be computed by adding the effects of the individual actions. We show how queries about additive fluents can be answered using the Causal Calculator. The examples discussed in this paper involve buying and selling, applying forces and moving groups of objects. The additive fluent mechanism can be used to instruct the Causal Calculator to generate more efficient plans.
6731652
Nonmonotonic causal theories
The nonmonotonic causal logic defined in this paper can be used to represent properties of actions, including actions with conditional and indirect effects, nondeterministic actions, and concurrently executed actions. It has been applied to several challenge problems in the theory of commonsense knowledge. We study the relationship between this formalism and other work on nonmonotonic reasoning and knowledge representation, and discuss its implementation, called the Causal Calculator.
6458022
Representing the Zoo World and the Traffic World in the language of the Causal Calculator
The work described in this report is motivated by the desire to test the expressive possibilities of action language C+. The Causal Calculator (CCALC) is a system that answers queries about action domains described in a fragment of that language. The Zoo World and the Traffic World have been proposed by Erik Sandewall in his Logic Modelling Workshop--an environment for communicating axiomatizations of action domains of nontrivial size.The Zoo World consists of several cages and the exterior, gates between them, and animals of several species, including humans. Actions in this domain include moving within and between cages, opening and closing gates, and mounting and riding animals. The Traffic World includes vehicles moving continuously between road crossings subject to a number of restrictions, such as speed limits and keeping a fixed safety distance away from other vehicles on the road. We show how to represent the two domains in the input language of CCALC, and how to use CCALC to test these representations.
19081367
Robust technique for estimating the bearings of cyclostationary signals
This paper deals with the problem of direction finding using cyclostationary signals in the presence of cycle frequency error (CFE). By exploiting the signal cyclostationarity, cyclic MUSIC and conjugate cyclic MUSIC presented in Gardner (Cyclostationarity in Communications and Signal Processing, New York, 1994; Proc. IEEE 76 (1988) 845) have been shown to be effective for signal-selective direction finding. However, they suffer from severe performance degradation even if there is a small error in the cycle frequency of the signals of interest. In this paper, we first evaluate the performance of conjugate cyclic MUSIC when CFE exists. An analytical formula is derived to show the behavior of the performance degradation due to CFE. By exploiting the eigenstructure of the conjugate cyclic correlation matrix of the received array data, we develop a technique including a method for estimating the cycle frequency of the SOI and an efficient method in conjunction with a subspace-fitting algorithm to achieve robust direction finding against CFE. Several simulation examples confirming the theoretical analysis and showing the effectiveness of the proposed technique are also presented.
9163139
Efficient instruction encoding for automatic instruction set design of configurable ASIPs
Application-specific instructions can significantly improve the performance, energy, and code size of configurable processors. A common approach used in the design of such instructions is to convert application-specific operation patterns into new complex instructions. However, processors with a fixed instruction bitwidth cannot accommodate all the potentially interesting operation patterns, due to the limited code space afforded by the fixed instruction bitwidth. We present a novel instruction set synthesis technique that employs an efficient instruction encoding method to achieve maximal performance improvement. We build a library of complex instructions with various encoding alternatives and select the best set of complex instructions while satisfying the instruction bitwidth constraint. We formulate the problem using integer linear programming and also present an effective heuristic algorithm. Experimental results using our technique generate instruction sets that show improvements of up to 38% over the native instruction set for several realistic benchmark applications running on a typical embedded RISC processor.
17546848
Analysis of Fuzzy Operators for High Quality Information Retrieval
Kim, M.H., J.H. Lee and Y.J. Lee, Analysis of fuzzy operators for high quality information retrieval. Information Processing Letters 46 (1993) 251-256. It has been argued that the conventional fuzzy set model based on the MIN and MAX operators is not appropriate for a model of information retrieval systems due to the properties of the MIN and MAX operators adverse to retrieval effectiveness. In this paper we investigate the behavioral aspects of various fuzzy operators and address the properties which are important in achieving high quality document rankings. We then present the fuzzy set model based on positively compensatory operators, which provides higher retrieval effectiveness than the conventional fuzzy set model. It is also described that the behavior of the proposed fuzzy set model almost coincides with that of the extended boolean model.
16485757
Reverse Engineering MAC
This paper reverse engineers backoff-based random-access MAC protocols in ad-hoc networks. We show that the contention resolution algorithm in such protocols is implicitly participating in a non-cooperative game. Each link attempts to maximize a selfish local utility function, whose exact shape is reverse engineered from the protocol description, through a stochastic subgradient method in which the link updates its persistence probability based on its transmission success or failure. We prove that existence of a Nash equilibrium is guaranteed in general. The minimum amount of backoff aggressiveness needed for uniqueness of Nash equilibrium and convergence of the best response strategy are established as a function of user density. Convergence properties and connection with the best response strategy are also proved for variants of the stochastic-subgradient-based dynamics of the game. Together with known results in reverse engineering TCP and BGP, this paper completes the recent efforts in reverse engineering the main protocols in layers 2-4.
16650023
Concurrent Static Single Assignment Form and Constant Propagation for Explicitly Parallel Programs
Static Single Assignment (SSA) form has shown its usefulness as a program representation for code optimization techniques in sequential programs. We introduce the Concurrent Static Single Assignment (CSSA) form to represent explicitly parallel programs with interleaving semantics and post-wait synchronization. The parallel construct considered in this paper is cobegin/coend. A new confluence function, the π-assignment, which summarizes the information of interleaving statements between threads, is introduced. The Concurrent Control Flow Graph, which contains information about conflicting statements, control flow, and synchronization, is used as an underlying representation for the CSSA from. An extension of the Sparse Conditional Constant propagation algorithm based on the CSSA form makes it possible to apply the constant propagation optimization to explicitly parallel programs.