Is the Rate in the source block a fixed rate?

Question

I have a simple source to sink model and I am merely altering the "Rate" to 6 per hour. I would expect a fixed 6 agents to be generated each hour, but it seems like in the first hour from 0 to 60min, only 3 agents are generated. Similarly in the time 60-120min, only 5 agents were generated.

Is there a warm up period in Anylogic or something like this that explains what is happening?

Answer 1

The source block doesn't produce exactly 6 agents per hour, it produces agents using a poisson distribution with mean 6 per hour (lambda=6). So the number of agents per hour you get will be random. But the reason why you always get 3 in the first hour and 5 in the second hour is that you have a fixed seed: You can find that option clicking on your simulation experiment under the randomness tab. If you change to random seed it will produce different agents per hour instead of always 3 and 5.

To produce EXACTLY 6 per hours you need to use an event. But first create a source that generates agents through injection:

And the event running 6 times per hour, adding 1 agent to the source:

Answer 2

Another alternative is to just use the interarrival time with a fixed time. This will give you the same results as Felipe's answer, but with one less object, as you will not need the event.

A few important items to note on this approach:

• Instead of 6.0, using a parameter would be better. You could call this parameter dArrivalsPerHour. This would make your source block easier to read in the future, and give you some better flexibility. Your interarrival time would be 1.0 / dArrivalsPerHour.
• Make sure you divide by at least (1) double. If you did 1/6, java would actually return 0! This is because in Java two integers divided by each other returns an integer, so java just truncates the decimal. If you use a parameter, just set its type to double. Usually to be extra careful against anyone accidentally changing my parameter type to integer in the future, I would still go ahead and use a 1.0.
• AnyLogic does not have an arrival at time zero in this approach. The first arrival would be at 0.166 hours. If you want an arrival at time zero, followed by this pattern (it would still be 6 per hour, just shifting when it starts), then you have a couple of options. First, you can use Felipe's approach and set the first occurrence time to zero. An alternative would be to could call an inject On Startup OR after you have finished any initialization code your model has.

Happy Modeling!