allow edge case of negative binomial with 0 mean

[sbfnk]

This is how R handles it and I see no reason not to support this here instead of throwing an error

> rnbinom(n = 1, mu = 0, size = 1)
[1] 0

[seabbs]

I think stan sees a reason (for whatever reason): "Error : Exception: Exception: neg_binomial_2_rng: Location parameter is 0, but must be > 0! (in 'functions/observation_model.stan' at line 117; included from 'model_estimate_infections' at line 7)"

[sbfnk]

I think stan sees a reason (for whatever reason): "Error : Exception: Exception: neg_binomial_2_rng: Location parameter is 0, but must be > 0! (in 'functions/observation_model.stan' at line 117; included from 'model_estimate_infections' at line 7)"

Exactly - which will no longer occur once this is merged.

[seabbs]

Sorry, my point was why does it do this and not follow the behaviour of R.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 7cc0d62 is merged into develop:

•   :ballot_box_with_check:default: 54.5s -> 53.9s [NANaN%, NANaN%]
•   :ballot_box_with_check:no_delays: 42.7s -> 44.9s [NANaN%, NANaN%]
•   :ballot_box_with_check:random_walk: 11.8s -> 14.3s [NANaN%, NANaN%]
•   :ballot_box_with_check:stationary: 27.9s -> 27.9s [NANaN%, NANaN%]
•   :ballot_box_with_check:uncertain: 58.6s -> 57.8s [NANaN%, NANaN%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 01246d8 is merged into develop:

•   :ballot_box_with_check:default: 51.6s -> 55.7s [NANaN%, NANaN%]
•   :ballot_box_with_check:no_delays: 45.7s -> 48.1s [NANaN%, NANaN%]
•   :ballot_box_with_check:random_walk: 18.8s -> 19.2s [NANaN%, NANaN%]
•   :ballot_box_with_check:stationary: 36.5s -> 31.6s [NANaN%, NANaN%]
•   :ballot_box_with_check:uncertain: 1m -> 56.6s [NANaN%, NANaN%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if f6a0334 is merged into develop:

•   :ballot_box_with_check:default: 49.8s -> 47.5s [-19.78%, +10.33%]
•   :ballot_box_with_check:no_delays: 37.3s -> 38.6s [-11.46%, +18.26%]
•   :ballot_box_with_check:random_walk: 11.8s -> 12.5s [-1.02%, +11.74%]
•   :ballot_box_with_check:stationary: 29.8s -> 31.5s [-4.68%, +15.99%]
•   :ballot_box_with_check:uncertain: 47.9s -> 44.5s [-17.57%, +3.53%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[seabbs]

This looks good I think. Just needs a news file entry before it can be merged..

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 11c6fbc is merged into main:

•   :ballot_box_with_check:default: 46.3s -> 44.1s [-13.52%, +4.36%]
•   :ballot_box_with_check:no_delays: 38.7s -> 39.7s [-9.75%, +14.71%]
•   :ballot_box_with_check:random_walk: 13s -> 13.3s [-7.16%, +12.52%]
•   :ballot_box_with_check:stationary: 32.1s -> 30.4s [-17.8%, +6.68%]
•   :ballot_box_with_check:uncertain: 46.6s -> 50.3s [-1.3%, +17.36%]
  Further explanation regarding interpretation and methodology can be found in the documentation.