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 before making a pull request I want to see how robust the performance is.

Hence I’m reaching out to the community in case you have a second to give it a try on a sophisticated model that you might happen to have lying around. I’m hoping to get the summaries for the adaptation parameters and the effective sample size and effective sample size per time for current develop and this new branch.

For example in CmdStan the comparison might look like

```
git clone git@github.com:stan-dev/cmdstan.git (if you has SSH set up on GitHub)
git clone https://github.com/stan-dev/cmdstan (otherwise)
cd cmdstan
git submodule update --init --recursive
make build
make CC=clang++ -j4 O=3 <MODEL_NAME>
./<MODEL_NAME> <cmdstan options>
# Compute sampler parameter summaries
../../../bin/stansummary output.csv | awk 'NR > 5 && NR < 15 {print $0}'
# Compute sum of effective sample sizes
../../../bin/stansummary output.csv | awk 'NR > 14 && NR < 115 {sum += $8} END {print sum}'
# Compute sum of effective sample sizes per time
../../../bin/stansummary output.csv | awk 'NR > 14 && NR < 115 {sum += $9} END {print sum}'
cd stan
git checkout feature/updated_stepsize_adapt_target
cd ..
make clean-all
make build
make CC=clang++ -j4 O=3 <MODEL_NAME>
./<MODEL_NAME> <cmdstan options>
# Compute sampler parameter summaries
../../../bin/stansummary output.csv | awk 'NR > 5 && NR < 15 {print $0}'
# Compute sum of effective sample sizes
../../../bin/stansummary output.csv | awk 'NR > 14 && NR < 115 {sum += $8} END {print sum}'
# Compute sum of effective sample sizes per time
../../../bin/stansummary output.csv | awk 'NR > 14 && NR < 115 {sum += $9} END {print sum}'
```

but comparisons run in any interface are welcome provided the above information can be communicated.

Thanks to any volunteers to are able to produce comparisons and those who make an attempt!