Question about LFO-CV vignette

General
1

I am just learning LOO and I’m going through LFO-CV vignette and wondering if I am misinterpreting what is happening. It looks like the log likelihoods are being passed into the PSIS function directly in creating the approximate 1-step ahead predictions instead of the log ratios. They are called log ratios, but I don’t see anywhere in code where the likelihoods are transformed into log ratios by multiplying -1. Do they need to be log ratios for using PSIS function, or does PSIS take log likelihood directly?

Thanks for the attention.

2

The difference comes as we are adding observations instead of removing them.