adapt_delta is the target average
proposal acceptance probability for adaptation. adapt_delta is
ignored if algorithm is not "sampling".The default value of adapt_delta is 0.95, except when the prior for
the regression coefficients is R2, hs,
hs_plus, or student_t with df <= 2<="" code="">, in
which case the default is 0.99.
In general you should not need to change adapt_delta unless you see a
warning message about divergent transitions, in which case you can increase
adapt_delta from the default to a value closer to 1 (e.g. from
0.95 to 0.99, or from 0.99 to 0.999, etc). The step size used by the
numerical integrator is a function of adapt_delta in that increasing
adapt_delta will result in a smaller step size and fewer divergences.
Increasing adapt_delta will typically result in a slower sampler, but
it will always lead to a more robust sampler.