Venkata S. Sarma Yadavalli

A STUDY ON A TWO UNIT STANDBY SYSTEM WITH ERLANGIAN REPAIR TIME

A two-unit cold standby system is considered. The failure rate of a unit is a constant and the repair time distribution is a two-stage Erlang distribution. Measures of system performance such as reliability, mean time before failure, system availability, and steady-state availability are derived. Also, a consistent asymptotically normal estimator and a 100(1-α)% asymptotic confidence interval for the steady-state availability of the system are obtained.

Poverty in South Africa – a statistical analysis

Poverty is one of the major challenges facing democratic South Africa. This article focuses on poverty in South Africa, using the Income and Expenditure Survey conducted in 1995 by Statistics South Africa (formerly the Central Statistical Service). In the first part, different approaches that can be followed in the measurement of poverty are discussed. In the second part, Sens approach to the measurement of poverty and the Chi-square Automatic Interaction Detection (CHAID) technique have been used to analyse the above data. CHAID is used to explore the relationship between the poverty status of the household (ie poor or non-poor) and other household characteristics. These variables can then be used as predictors of poverty status.

Software reliability growth model with change-point and effort control using a power function of the testing time

Many software reliability growth models (SRGMs) based on a non-homogenous Poisson process (NHPP) have been developed with the assumption of a constant fault detection rate (FDR) and a fault detection process dependent only on the residual fault content. In this paper we develop a SRGM based on NHPP using a different approach for model development. Here, the fault detection process is dependent not only on the residual fault content, but also on the testing time. It incorporates a realistic situation encountered in software development where the fault detection rate is not constant over the entire testing process, but changes due to variations in resource allocation, defect density, running environment and testing strategy (called the change-point). Here, the FDR is defined as a function of testing time. The proposed model also incorporates the testing effort with the change-point concept which is useful in solving the problems of runaway software projects and provides the testing effort control technique and flexibility to project managers to obtain the desired reliability level. It utilizes failure data collected from software development projects to show its applicability and effectiveness. The statistical package for social sciences (SPSS) based on the least-squares method has been used to estimate unknown parameters. The mean squared error (MSE), relative predictive error (RPE), average mean squared error (AMSE) and the average relative predictive error (ARPE) have been used to validate the model. It is observed that the proposed model results are accurate, highly predictive and incorporate industrial software project concepts.

Alternative hyper-heuristic strategies for multi-method global optimization

The purpose of this paper is to investigate the use of meta-heuristics as low-level heuristics in a hyper-heuristic framework. A novel multi-method hyper-heuristic algorithm which makes use of a number of common meta-heuristics is presented. Algorithm performance is evaluated on a diverse set of real parameter benchmark problems and meaningful conclusions are drawn with respect to the selection of alternative low-level heuristics and the acceptance of the obtained solutions within the proposed multi-method meta-heuristic approach.

On allocation of resources during testing phase of a modular software

To provide reliable software, it is tested over a wide range of testing environment. In the process, testing resources such as time, testing personnel etc. are used. These resources are not infinitely large and therefore need to be used judiciously. In this article, we discuss the testing resource allocation problem among modules to maximize the total fault removal from software consisting of several independent components (modules). For the resulting optimization problem, we define marginal testing effort function (MTEF), where the testing resource consumption is represented in terms of fault removal. The three MTEFs proposed in this article account for both exponential and S-shaped growth curves, which are commonly used in software reliability analysis. Results are illustrated numerically using different data sets.

Bayesian Study Of A Two-Component System With Common-Cause Shock Failures

The steady-state availability of a two-component system in series and parallel subject to individual failures (I-failures) and common-cause shock (CCS) failures is studied from a Bayesian viewpoint with different types of priors assumed for the unknown parameters in the system. Monte Carlo simulation is used to derive the posterior distribution for the steady-state availability and subsequently the highest posterior density intervals. A numerical example illustrates the results.

Two substitutable perishable product disaster inventory systems

A disaster inventory system is considered in which two substitutable items are stored for disaster management. In the event of disaster management, a particular product may become stock-out and the situation warrants that a demand for the particular product during its stock-out period may be substituted with another available similar product in the inventory. From the utility point of view, continuous review inventory models are quite appropriate in disaster inventory management. In this paper, a continuous review two substitutable perishable product disaster inventory model is proposed and analyzed. Since the inventory is maintained for disaster management, an adjustable joint reordering policy for replenishment is adopted. There is no lead time and the replenishment is instantaneous. For this model, some measures of system performance are obtained. The stationary behavior of the model is also considered. Numerical examples are also provided to illustrate the results obtained.

Investigating the impact of alternative evolutionary selection strategies on multi-method global optimization

Algorithm selection is an important consideration in multi-method global optimization. This paper investigates the use of various algorithm selection strategies derived from well known evolutionary selection mechanisms. Selection strategy performance is evaluated on a diverse set of floating point benchmark problems and meaningful conclusions are drawn with regard to the impact of selective pressure on algorithm selection in a multi-method environment.

Heuristic space diversity control for improved meta-hyper-heuristic performance

This paper expands on the concept of heuristic space diversity and investigates various strategies for the management of heuristic space diversity within the context of a meta-hyper-heuristic algorithm in search of greater performance benefits. Evaluation of various strategies on a diverse set of floating-point benchmark problems shows that heuristic space diversity has a significant impact on hyper-heuristic performance. An exponentially increasing strategy (EIHH) obtained the best results. The value of a priori information about constituent algorithm performance on the benchmark set in question was also evaluated. Finally, EIHH demonstrated good performance when compared to a popular population based algorithm portfolio algorithm and the best performing constituent algorithm.

Multi-Item Deterministic Fuzzy Inventory Model

In this note, a fuzzy inventory model with multiple items is considered. Economic order quantities (EOQs) are developed for these items. The costs involved in inventory are always assumed to be exact, otherwise called as crisp or hard, but in practice these costs are not exact or precise but vary over a range. In such cases an application of fuzzy set theory plays a vital role in obtaining the EOQ. An application of this model to manpower planning is studied with an example; sensitivity analysis is also made.