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I want to remove all randomization from my Repast model so that I can refactor with confidence that functionality is unchanged. However, I was unable to remove randomization by setting the seed using RandomHelper.setSeed(1) at the top of myBuilder.build(), and making sure that my 'Default Random Seed' parameter seed was set to 1 in the GUI at initialization.

So, I tried to remove randomization from the sample JZombies model and had the same issue. Again, I set RandomHelper.setSeed(1) at the top of JZombiesBuilder.build(), and made sure the Default Random Seed was set to 1. Sometimes the output was identical, sometimes it was not.

In both cases I'm using a Text Sink to record a constant number of ticks of aggregate agent counts and aggregate agent attributes as my data. I found differences in the output files using both Windows's FC & FCIV.

What changes do I need to make to ensure deterministic behavior?

Edit:

I got deterministic behavior in the JZombies demo model by also putting RandomHelper.setSeed(1); at the top of each class's constructor. Doing the same thing in my actual model makes the first step consistently identical. There are still differences from the second tick on. I think the issue is random scheduling, now?

Willow Treeman
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You should not have to set your random seed twice, so I would start with removing the RandomHelper.setSeed(1) call in your builder (and elsewhere). The GUI random seed you are mentioning is set via the JZombies_Demo.rs/parameters.xml file.

On to your actual question. If you are using RandomHelper calls for all of your stochastic elements in the code, you should see reproducible results. If not, this could indicate that there is some unaccounted for stochasticity, e.g., the use of a non-RandomHelper call or something like iterating through a HashMap. E.g., when you iterate using the for loop over a DefaultContext, the iteration occurs over a HashSet, but when using the Context.getObjects() method, the internal iteration is over a LinkedHashMap, so repeatability is ensured.

J. Ozik
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  • Is what you're saying that to ensure deterministic behavior, I need to remove all uses of HashMap and use LinkedHashMap instead? And this means never doing `for (Object obj : context) { //stuff }` ? – Willow Treeman May 30 '20 at 20:20
  • Are the spatial queries MooreQuery() and VNQuery() issues for the same reason? If so, how do I use them in a deterministic way? – Willow Treeman May 30 '20 at 23:12
  • Yes `for (Object obj : context) { //stuff }` will potentially break reproducibility. You should use `Context.getObjects()` instead. The spatial queries should not produce any reproducibility issue but if you are seeing something like that, please let us know and, if possible, provide a small example that shows this. – J. Ozik May 31 '20 at 03:52