Why is the number of raw data points, twice the amount of "draws"?

Questions
1

For example, if I called this code:

with model_method:
    trace = pm.sample(draws=2500, tune=1000, cores=1)

print(len(trace['theta'][:, 0]))

It reports that the length of trace[‘theta’][:, 0] as 5000, which is 2x the draws (2500). I was wondering why that was the case.

2

Sounds like you’re running two chains. By default:

If [chains=]None, then set to either cores or 2, whichever is larger. For SMC the number of chains is the number of draws.

So you’re doing 2500 draws each from 2 chains, so 5000 draws total. Set chains=1 to have it match; or draws=int(N/nchain), chains=nchain if you want to be able to check for consistent sampling across restarts.