Progress message ratio_divergent_transitions_during_adaption bug

[sefffal]

This is difficult to demonstrate, but I believe the value of ratio_divergent_transitions_during_adaption printed during sampling when progress=true is currently incorrect.

The behaviour I've seen is:

1. During adaptation, numerical errors are encountered causing ratio_divergent_transitions_during_adaption to increase
2. By the end of adaptation, the numerical errors stop
3. Sampling continues after adaptation and ratio_divergent_transitions stays zero.
4. ratio_divergent_transitions_during_adaption starts to drop (even though adaptation is now finished!) until it reaches a lower value, eg 50% lower if there are equal numbers of samples during and after adaptation.

I couldn't find the right location in the code, but I believe that ratio_divergent_transitions_during_adaption might be calculating the ratio using the total number of samples so far, and not stopping updating after adaptation completes.

[sefffal]

I think I see the issue:
https://github.com/TuringLang/AdvancedHMC.jl/blob/2b3814ccbb36806eb0f21c2c937146606a873884/src/sampler.jl#L198C1-L199C62

percentage_divergent_transitions = num_divergent_transitions / I
percentage_divergent_transitions_during_adaption =
    num_divergent_transitions_during_adaption / i

should instead be:

percentage_divergent_transitions = num_divergent_transitions / I
percentage_divergent_transitions_during_adaption =
    num_divergent_transitions_during_adaption / min(i, n_adapts)

[sefffal]

Bump on this issue; it's minor but the fix is one line! Thanks.

[torfjelde]

Oh, good catch @sefffal ! Would you mind making a PR or you want one of us to just do it?:)