Ordering Events

[ChrisF]

Hi. I'm new to Vensim (using PLE) and currently evaluating this System Dynamics software to see whether it will suit my needs for a large simulation project. I am very much at the start of the learning curve as a user and currently playing with equations.

I wonder whether it is possible to use a formula to order events so that these occur in a chosen sequence over time. For example, I am looking at an example in construction and need to transport materials (which will vary in quantity according to demand) to a site in a particular sequence. E.g. Stage 1 (material a / 25 per load @ 5 loads per day), when that is complete Stage 2 (material b / 10 per load @ 8 loads per day), when that is complete Stage 3 (c/ 30 per load @ 3 loads per day)... etc. I would like to be able to see the pattern of loads over time as well as the stock of materials accumuating at the site.

Thanks
Chris

[Administrator]

If I were implementing something like this, I'd use subscripting to look at each stage (and subscripts are not available in PLE).

Possibly have a stock which is "materials required" (subscripted by stage). This gets drained until the materials stock is empty, then start the flow of the next stage. Vensim ships with a sample model called "tubs" which looks at each tub of water filling one after the other, it would be easy to adapt that model so it does what you describe instead.

In PLE you can do something similar, but would need multiple IF THEN ELSE statements to work out when each stage starts. I'll see if I can come up with something for you.

[ChrisF]

Thanks.
The model you refer to, Tubs, can't be opened by PLE. Or rather, it can be opened but can not be run.

[Administrator]

Here is a quick demo of what I think you are trying to achieve.

It's only for two phases, as I said if I were doing it, I'd subscript the model so you could have any number of phases.

forumdemo.mdl

(3.34 KiB) Downloaded 223 times

[tomfid]

This could also be done in Ventity.