Connecting forward and backward autoregressive models

The aim of this paper is to describe procedures for computing the matrix polynomial defining a vector backward autoregressive recursion from the matrix polynomial defining a vector forward autoregressive recursion. Direct procedures for computing the backward polynomial which do not involve a solution of a matrix Lyapunov equation are described. A novel interpretation is also included of a known procedure which involves the computation of covariance data via the matrix Lyapunov equation. This procedure depends on a standard result connecting forward and reverse time state-space models. A comparison involving operation counts is given of the algorithms.     

Requirements analysis using forward and backward search

The requirements analysis of critical software components often involves a search for hazardous states and failure modes. This paper describes the integration of a forward search for consequences of reaching these forbidden modes with a backward search for contributing causes. Results are reported from two projects in which the integrated search method was used to analyze the requirements of critical spacecraft software. The search process was found to be successful in identifying some ambiguous, inconsistent, and missing requirements. More importantly, it identified four significant, unresolved requirements issues involving complex system interfaces and unanticipated dependencies. The results suggest that recent efforts by researchers to integrate forward and backward search have merit.     

前向切片与后向切片之间关系的研究

前向切片和后向切片是两种不同的切片技术,为了研究它们之间的异同,通过实验,得到两个结论：后向切片分析的平均缩减率等于前向切片分析的平均缩减率;后向切片分析的缩减率较均衡,前向切片分析的缩减率变化较大,极端情况较多。     

The forward and backward processes in health policy planning

This is a study of a legislative conflict over the National Health Insurance policy played out in the 96th Congress of the United States. It attempted to find out whether the policy aimed at restructuring the U.S. health care system was possible. Since previous analysis concluded that the Kennedy NHI plan was such an innovative policy the questions examined here were: (1) Would the Kennedy plan emerge as the adopted national policy? (2) If not, what plan could be a compromise proposal?To answer the first question the forward process of planning was applied. The conflict was structured according to the levels of a conceptual hierarchy. The focus of the hierarchy constituted the first level, the actors involved the second, their objectives and subobjectives formed the third and fourth levels, and the policies pursued by the actors (the NHI proposals) the fifth level. The elements of each level were weighed according to their relative importance by using the principal eigenvectors of a series of pairwise comparison matrices. The priority of the NHI plans promoted by the particular groups was derived on the assumption that a plan with the highest eigenvector will probably emerge as the adopted national health policy. The forward process answered the question: Given the present actors, their objectives, and the strength to influence the outcome, which NHI plan was the most likely to emerge as the adopted national policy?To answer the second question the backward process of planning was applied. It was an attempt to find a compromise solution acceptable to all the parties involved.This method of policy design, developed by Thomas L. Saaty, has great advantages over the traditional methods of policy planning. It brings into focus the matrix of competing interests and sets firm boundaries for planning efforts. It helps in setting pragmatic, not romantic policies, with a great saving of time and money.     

Evaluation of a supermarket twin-checkout involving forward and backward operation

Cashier workplaces recently put into service in self-service shops of a retail company provide a face-to-face position of two cashiers. These twin-checkouts involve both traditional goods handling from the front to the rear as well as a reverse technique - i e, forward operation from behind. By means of different methods they have been analysed from an ergonomics point of view and evaluated in respect of operators' workload resulting from the specific layout. The results support the conclusion that the new 'backward' system and twin-checkouts are not inferior to traditional single checkouts. On the contrary, a working technique where the arm moves from behind to the front involves a better approach to accounting for physiological characteristics and obviously allows a better fitting of the task of operators.     

Comparative study of finite difference approaches in simulation of magnetohydrodynamic turbulence at low magnetic Reynolds number

Two approaches to finite difference approximation of turbulent flows of electrically conducting incompressible fluids in the presence of a steady magnetic field are analyzed. One is based on high-order approximations and upwind-biased discretization of the nonlinear term. Another is consistently of the second order and nearly fully conservative in regard of mass, momentum, kinetic energy, and electric charge conservation principles. The analysis is conducted using comparison with high-accuracy spectral direct numerical simulations of channel flows with wall-normal and spanwise magnetic fields. Focus of the analysis is on the quality of finite difference approximation in the situation when the magnetic field leads to significant transformation of the flow structure. In the case of turbulent flows at moderate magnetic fields, the conservative scheme approach offers better stability and equal or higher accuracy than the approach based on the upwind discretization. The conservation property is expected to become increasingly important and even indispensable at stronger magnetic fields.     

Dealing with forward and backward jumps in workflow management systems

Workflow management systems (WfMS) offer a promising technology for the realization of process-centered application systems. A deficiency of existing WfMS is their inadequate support for dealing with exceptional deviations from the standard procedure. In the ADEPT project, therefore, we have developed advanced concepts for workflow modeling and execution, which aim at the increase of flexibility in WfMS. On the one hand we allow workflow designers to model exceptional execution paths already at buildtime provided that these deviations are known in advance. On the other hand authorized users may dynamically deviate from the pre-modeled workflow at runtime as well in order to deal with unforeseen events. In this paper, we focus on forward and backward jumps needed in this context. We describe sophisticated modeling concepts for capturing deviations in workflow models already at buildtime, and we show how forward and backward jumps (of different semantics) can be correctly applied in an ad-hoc manner during runtime as well. We work out basic requirements, facilities, and limitations arising in this context. Our experiences with applications from different domains have shown that the developed concepts will form a key part of process flexibility in process-centered information systems. Received: 6 October 2002 / Accepted: 8 January 2003 Published online: 27 February 2003 This paper is a revised and extended version of [40]. The described work was partially performed in the research project “Scalability in Adaptive Workflow Management Systems” funded by the Deutsche Forschungsgemeinschaft (DFG).     

Numerical schemes for the forward–backward heat equation

This paper is concerned with a class of forward–backward heat equations. We use Saulyev's scheme to formulate certain approximation schemes. Then a non-overlap domain decomposition method is presented for the numerical solution. The numerical experiments show that the given algorithm is feasible and effective.     

基于前向-后向HMM的连续语音识别系统的研究

在分析语音识别原理的基础上采用TMS320DM642 DPS芯片,利用前向-后向HMM声学模型和Viterbi算法进行模式训练和识别,设计了一种连续的、小词量的语音识别系统.实验结果表明,该语音识别系统具有较高的识别率和一定程度的鲁棒性,实验室识别率和室外识别率分别达到96.8%及91.2%,该语音识别系统具有良好的实用性和可移植性.     

Comparative study of matrix refinement approaches for ensemble clustering

Machine Learning - Cluster ensembles or consensus clusterings have been shown to be better than any standard clustering algorithm at improving accuracy and robustness across various sets of data....     

Toward orthogonal non-individualised head-related transfer functions for forward and backward directional sound: cluster analysis and an experimental study

Individualised head-related transfer functions (HRTFs) have been shown to accurately simulate forward and backward directional sounds. This study explores directional simulation for non-individualised HRTFs by determining orthogonal HRTFs for listeners to choose between. Using spectral features previously shown to aid forward–backward differentiation, 196 non-individualised HRTFs were clustered into six orthogonal groups and the centre HRTF of each group was selected as representative. An experiment with 15 listeners was conducted to evaluate the benefits of choosing between six centre-front and six centre-back directional sounds rather than the single front/back sounds produced by MIT-KEMAR HRTFs. Sound localisation error was significantly reduced by 22% and 65% of listeners reduced their front–back confusion rates. The significant reduction was maintained when the number of HRTFs was reduced from six to five. This represents a preliminary success in bridging the gap between individual and non-individual HRTFs for applications such as spatial surround sound systems.

Statement of Relevance:Due to different pinna shapes, directional sound stimuli generated by non-individualised HRTFs suffer from serious front–back confusion. The reported work demonstrates a way to reduce front–back confusion for centre-back sounds generated from non-individualised HRTFs.     

Effects of visual referencing on backward and forward treadmill walking in VR environments

Backward walking is used increasingly as a rehabilitation exercise for stroke and diabetic peripheral neuropathy patients to improve strength and balance. However, it is unclear how visual referencing affects backward and forward walking. In this study, we evaluated spatiotemporal gait characteristics changes due to visual referencing while backward/forward walking. Sixteen healthy young participants were recruited in this study. All participants walked for 2 min with and without visual referencing in the virtual reality environment. While walking backward participants faced the virtual reality screen similar to forward walking, but their treadmill belt direction of movement was reversed. All participants walked at their preferred speed. We found that backward walking with visual reference affected symmetry in step length (p < 0.05) and step width (p < 0.001). Backward walking increased variability in step length (p < 0.001) and COM side excursions (p < 0.01) but also increased base of support through increased step width (p < 0.02). We also found backward walking with visual reference had significantly increased double support time (p < 0.001) and reduced swing time (p < 0.001). We also found that backward walking does not predispose to slip and trip risk, thereby, reduced foot contact velocity (p < 0.0001) and increased foot clearance (p < 0.0001). The findings of this study will help understand the effects of visual reference in backward and forward walking enables clinicians to design patient-centered rehabilitation exercises.     

Detection of nonlinear FM signals via forward–backward cost-reference particle filter

Many applications require the detection of unknown nonlinear frequency modulated (FM) signals in noise. In this paper, a nonlinear FM signal in one time interval is approximated by linear FM (LFM) segments in successive subintervals. Each LFM segment is parameterized by a 2-dimensional (2D) state vector and its evolution from a subinterval to the next one is modeled as a dynamic system of unknown statistics with linear state transition equations and nonlinear measurement equations. A forward–backward cost-reference particle filter (FB-CRPF) is proposed to estimate the state sequence. From the estimated state sequence, the generalized likelihood ratio test (GLRT) statistic and the total variation (TV) statistic are computed for signal detection. In the 2D feature plane of the GLRT versus TV, the decision region of the null hypothesis at a given false alarm rate is determined by the 2D convexhull learning algorithm from noise-only training samples. Two kinds of simulated signals are used to test the proposed detector and results show that the proposed detector attains better performance than the two existing detectors.     

New automatic forward and backward blind sources separation algorithms for noise reduction and speech enhancement

In this paper, we consider the speech enhancement problem in a moving car through a blind source separation (BSS) scheme involving two spaced microphones. The forward and backward blind source separation structures often use manual voice activity detector (MVAD) systems to control the adaptation of the separating adaptive filters. In this paper, we propose two new automatic voice activity detector (AVAD) systems that allow adapting the original forward and backward BSS structures automatically. The proposed AVAD systems are based on the use of the forward BSS structure to estimate the optimal values of the separating adaptive filters step-sizes. Moreover, the new proposed algorithms are stable and could be used even in very noisy conditions. Intensive experiments are carried out with these two new proposed algorithms to validate their good performances in speech enhancement and noise reduction applications. The presented experiments are based on the system mismatch, the cepstral distance and the output signal-to-noise ratio criteria evaluations. The obtained results show the good performances of the proposed algorithms in comparison with their original versions, where manual VAD systems are used.     

Production system-based simulation for backward on-line job change scheduling

Backward on-line job change scheduling, referring to the on-line job change scheduling of a current processing step to satisfy the job change schedule of the subsequent processing step, is a common problem in modern Fabs. In this research, the production system-based simulation methodology is proposed to solve the backward on-line job change scheduling problem. This simulation is processed by the state change that is caused by an execution of the operator, and it finds the schedule with the best handle values considering the current status. Several simulation runs with diverse handle values were required to find the best values because the status of the shop floor can change dynamically. To validate the simulation, this production system-based simulation is applied to the on-line job change scheduling of a tire belt processing step as part of the tire manufacturing process.     

Modes of simulation practice: approaches to business and military simulation

Although simulation is performed in a wide range of disciplines there has been almost no debate about the practice of simulation across these domains of application. This paper concentrates on two domains of practice, business and military simulation, and identifies three modes of practice: simulation as software engineering, simulation as a process of organisational change and simulation as facilitation. The facets of each of these modes of practice are described, and the predominant usage of the modes in business and the military are identified. The implications for simulation software suppliers, practitioners, researchers, educators and users are discussed.     

A note on fractional differences based on a linear combination between forward and backward differences

Two fractional differences based on a linear combination between forward and backward differences are defined. Also, the exponent laws for these are proved simply. Finally, the Leibniz rules for the special cases are presented.     

Matrix stability of the backward differentiation formula in electrochemical digital simulation

The matrix stability of the backward differentiation formula (BDF) algorithm for the numerical solution of the reaction–diffusion partial differential equations arising in electrochemistry, as a function of the number of time levels k and under several boundary conditions, was studied. The study included also the two-species catalytic mechanism, and unequal intervals (nonuniform spatial grid). The method is unconditionally stable in all cases for k⩽7 (that is, order ⩽6) irrespective of the rate of homogeneous chemical reactions or boundary conditions. Homogeneous chemical reactions, except in the case of the two-species catalytic reaction, were found to have a stabilising effect.