Last in First out Queues

[chester riddalls]

Are there any plans to provide a queue function that operates on a last in first out principle? This would be very useful for modelling date life waste in inventory stocks: Customers tend to look for the youngest goods on a supermarket shelf. This is hard to replicate using the standard vensim queue.

[bob@vensim.com]

Oddly enough, this is one situation where any built in function would likely be inferior to a classic system dynamics formulation. This is because only some customers pick the freshest products, and only some of the workers properly restock with the fresh goods behind. Thus you end up with an oddball ageing problem.

The best approach is to use a coflow on ageing (see the maintenance model example that comes with Vensim) and then to assign a rotation effectiveness that can be used to compute spoilage. Pull that age down by the shelf life on spoilage.

I hope that is helpful.

[chester riddalls]

Thanks for your thoughts.
Unfortunately, I've opted against an SD approach for this problem for a number of reasons: I am looking to get recommendations for individual SKUs and so the model tracks the flow of 1 product rather than a group of products. Therefore the delays are discrete rather than distributed.
Some parts of the supply chain have highly 'discrete' processes that operate on individual batches of product one at a time. I think it would be very difficult to approximate these processes using a lag type approach.
Never mind - coflows it is!