Confused about accept_stat__ and delta

[mitzimorris]

for the above example, the Bernoulli model is too easy to fit, so it’s not a good test case.

@betanalpha has been discussing this issue and is working on tweaks -

Step size adaptation targets wrong optimality criterion

Request for Volunteers to Test Adaptation Tweak

Recently I realized that our adaptation target, which is a heuristic proxy meant to mimic a Metropolis acceptance probability, might be too conservative, ultimately giving a step size that’s smaller than necessary which itself results in lower effective sample sizes and more expensive numerical integrations. I’ve implemented what I believe is a more appropriate adaptation target in stan-dev/stan:feature/updated_stepsize_adapt_target and preliminary results confirm the theoretical intuition, but…