Inventory models need some specification of the distribution of demand in order to find the optimal order-up-to level or reorder point. This distribution is unknown in real life and there are several solutions to overcome this problem. One approach is to assume a distribution, estimate its...

Horizontal collaboration between companies has been recognized as beneficial, although implementing horizontal collaboration has proven to be challenging. In this paper, we zoom in on the largest challenges and present a holistic approach to foster horizontal collaboration. Specifically, we...

Adjustable robust optimization (ARO) is a technique to solve dynamic (multistage) optimization problems. In ARO, the decision in each stage is a function of the information accumulated from the previous periods on the values of the uncertain parameters. This information, however, is often...

In this paper we use Lagrange interpolation polynomials to obtain good gradient estimations. This is e.g. important for nonlinear programming solvers. As an error criterion we take the mean squared error. This error can be split up into a deterministic and a stochastic error. We analyze these...

In this paper we analyze different schemes for obtaining gradient estimates when the underlying function is noisy. Good gradient estimation is e.g. important for nonlinear programming solvers. As an error criterion we take the norm of the difference between the real and estimated gradients. This...

In inventory management, hierarchical forecasting (HF) is a hot issue: families of items are formed for which total demand is forecasted; total forecast then is broken up to produce forecasts for the individual items. Since HF is a complicated procedure, analytical results are hard to obtain;...

The exact expressions for the convolutions of gamma distributions with different scale parameters is quite complicated. The approximation by means of another gamma distribution is shown to be remarkably accurate for wide ranges of the parameter values, especially if more than two random...

For a number of statistical applications, experts' subjective estimates are needed for distributional parameters, like mean and variance; sometimes even the whole density is wanted. The literature agrees that it is wise behaviour to ask the expert only quantile estimates; from these, the desired...

Production Planning and Inventory Control (PPIC) is an essential dynamics of the logistical performance of manufacturing organizations. In this paper, we discuss the development of a PPIC system in a process industry. The process manufacturing industry has not embraced the new Advanced Planning...

To model demand, the normal distribution is by far the most popular; the disadvantage that it takes negative values is taken for granted. This paper proposes two modifications of the normal distribution, both taking non-negative values only. Safety factors and order-up-to-levels for the familiar...