Revisiting the PERT mean and variance

Difficulties with the interpretation of the parameters of the beta distribution let Malcolm et al. (1959) to suggest in the Program Evaluation and Review Technique (PERT) their by now classical expressions for the mean and variance for activity completion for practical applications. In this note, we shall provide an alternative for the PERT variance expression addressing a concern raised by Hahn (2008) regarding the constant PERT variance assumption given the range for an activity’s duration, while retaining the original PERT mean expression. Moreover, our approach ensures that an activity’s elicited most likely value aligns with the beta distribution’s mode. While this was the original intent of Malcolm et al. (1959), their method of selecting beta parameters via the PERT mean and variance is not consistent in this manner.     

PERT问题的新算法

本文给出了一种通过求解最长路径解决 PERT问题的新算法 .其优点是 ,编制运算程序之前 ,无需做出系统作业的网络图 ,因此 ,使用起来更加方便     

A project game for PERT networks

An important topic in PERT networks is how to allocate the total expedition (or delay) for situations in which the project is not executed as planned. In order to do that we define a TU project game that satisfies some desirable properties from the management project and game theory point of view.     

计划评审技术的改进

由于计划评审技术存在的不足,导致项目管理存在一定的偏差.对计划评审技术中的活动期望时间和方差的公式做了改进,从而提高了项目管理的精确性.还指出计划评审技术中活动期望时间和方差的计算公式,实际上是改进后公式的特殊情形.     

非肯定型PERT网络分析

本文用一个具体示例说明非肯定型PERT网络中原来一般方法的不足 ,提出用仿真方法解决这问题     

网络计划图的工序关系及其复杂性研究

本文研究了将原始的施工工序关系表转换为规范网络计划图的活动关系的算法.在理论上讨论了网络图中活动与紧前活动的关系以及与节点的关系,研究了网络图中添加虚活动的规律,进一步提出了生成网络计划图的按先行工序类生成算法的补充研究.     

PERT工序时间估计的一些研究

本文首先从理论上分析了在工序时间服从β—分布的条件下，传统的ＰＥＲＴ公式的估计误差，并指出其中的方差估计误差范围比较大．其次本文介绍了国外提出的若干工序时间估计改进方法，并对其相互优劣比较结果进行了评述．最后本文就工序时间估计的一些基本问题进行了讨论．     

学习曲线在成本计划评审应用

论文介绍了计划评审法(PERT)的基本思想,探讨了学习曲线模型在PERT图中的应用,并给出了相应实例.     

Recurrence set-relations in stochastic multiobjective dynamic decision processes

Finite horizon stochastic dynamic decision processes with R^p valued additive returns are considered. The optimization criterion is a partial-order preference relation induced from a convex cone in R^p . The state space is a countable set, and the action space is a compact metric spaces. The optimal value function, which is of a set-valued mapping, is defined. Under certain assumptions on the continuity of the reward vector and the transition probability, a system of a recurrence set-relations concerning the optimal value functions is given.     

Mixture densities for project management activity times: A robust approach to PERT

PERT is a widely utilized framework for project management. However, as a result of underlying assumptions about the activity times, the PERT formulas prescribe a light-tailed distribution with a constant variance conditional on the range. Given the pervasiveness of heavy-tailed phenomena in business contexts as well as inherently differing levels of uncertainty about different activities, there is a need for a more flexible distribution which allows for varying amounts of dispersion and greater likelihoods of more extreme tail-area events. In particular, we argue that the tail-area decay of an activity time distribution is a key factor which has been insufficiently considered previously. We provide a distribution which permits varying amounts of dispersion and greater likelihoods of more extreme tail-area events that is straightforward to implement with expert judgments. Moreover, the distribution can be integrated into the PERT framework such that the classic PERT results represent an important special case of the method presented here.     

A rule for slack allocation proportional to the duration in a PERT network

In this paper, we define a new rule for the resolution of the slack allocation problem in a PERT network. This problem exists of allocating existing extra time in some paths among the activities belonging to those paths. The allocation rule that we propose assigns extra time to the activities proportionally to their durations in such a way that no path duration exceeds the completion time of the whole project. This time allocation enables us to make a schedule for the PERT project under study. We give two characterizations of the rule and we compare it with others that have been previously defined in the literature.     

A note on Chern-Yamabe problem

We propose a flow to study the Chern-Yamabe problem and discuss the long time existence of the flow. In the balanced case we show that the Chern-Yamabe problem is the Euler-Lagrange equation of some functional. The monotonicity of the functional along the flow is derived. We also show that the functional is not bounded from below.     

A note on constant proportion trading strategies

We consider constant proportion (CP) trading strategies when there are multiple underlying securities and use a recently derived expression for the terminal wealth of a CP strategy to address two issues. First, we characterize the performance of a CP strategy relative to the performance of the corresponding buy-and-hold strategy. We then explain the performance of leveraged ETFs which have been criticized for not performing as expected, particularly during the financial crisis of 2008.     

A note on constant geodesic curvature curves on surfaces

In this paper we are concerned with the structure of curves on surfaces whose geodesic curvature is a large constant. We first discuss the relation between closed curves with large constant geodesic curvature and the critical points of Gauss curvature. Then, we consider the case where a curve with large constant geodesic curvature is immersed in a domain which does not contain any critical point of the Gauss curvature.     

A note on testing hypotheses for stationary processes in the frequency domain

In a recent paper, Eichler (2008) [11] considered a class of non- and semiparametric hypotheses in multivariate stationary processes, which are characterized by a functional of the spectral density matrix. The corresponding statistics are obtained using kernel estimates for the spectral distribution and are asymptotically normally distributed under the null hypothesis and local alternatives. In this paper, we derive the asymptotic properties of these test statistics under fixed alternatives. In particular, we also show weak convergence but with a different rate compared to the null hypothesis. We also discuss potential statistical applications of the asymptotic theory by means of a small simulation study.     

A note on the Sarmanov bivariate distributions

We investigate the maximum correlation for Sarmanov bivariate distributions with fixed marginals and strengthen the existing results in the literature. The improvement in the maximum correlation is significant. A characterization of the Sarmanov distribution via chi-square divergence is also given. This extends Nelsen [13] result about the Farlie-Gumbel-Morgenstern (FGM) distribution.     

A note on interval estimation of the standard deviation of a gamma population with applications to statistical quality control

Traditional process control charts for a measurement standard deviation are based on the assumption of normality, which may not always be valid. Assuming that measurements follow a gamma distribution, we have obtained an approximate distribution of the sample variance, scaled appropriately. This approximate distribution, which happens to be another gamma model, is used to derive an interval estimate of the population standard deviation. Further, the above approximate gamma model for the sample variance can be used to develop a process control chart as demonstrated by a simulated data set.