Clarify the difference between capacity and queue_size

[mtbakerguy]

When writing a simulation, it's easy to understand what capacity is. If you have four machines, you put four machines in capacity. However, it's less clear from the reference guide or the vignettes how you create a rejected seize request (in my case, this involved turning off queueing entirely). I found it eventually on the mailing list (https://groups.google.com/forum/#!topic/simmer-devel/povKK0WKyf4) but the right snippet of code or more details in the reference guide would've made it easier to understand.

[Enchufa2]

Did you check the examples under ?seize? One of them demonstrates how to use the reject argument.

[mtbakerguy]

I did. Perhaps the simplest thing to do would be something like the following in the example:

# set queue_size == 0 to ensure the reject path is taken
# when all capacity's used.
simmer() %>%
  add_resource("doctor", capacity=1, queue_size=0) %>%
  add_resource("nurse", capacity=10, queue_size=0) %>%
  add_generator("patient", traj, at(0, 1)) %>%
  run() %>% invisible

[Enchufa2]

I'll add some comments in the manual then, maybe also in add_resource.

Note also that turning off the queue is not needed for rejections to occur. In general, it may happen when queue_size is finite. E.g., if capacity=1 and queue_size=2 and 4 arrivals try to seize the resource, 1 is served, 2 wait in the queue and the 4th is rejected.