A gen_extreme_value() xi without a formula is sampled as brms
samples it, as tmp_xi on the whole line, mapped into the support the
current mu and sigma leave by brms's scale_xi(). Sampled on its
log1p scale, the support's edge is a wall in the sampled space: on
the review's data (n = 40, y ~ 1, 4 chains x 2000) 3388 of 4000
transitions diverged at xi = -0.85, and none did through tmp_xi
(dev/famuni-out/tmpxi.txt).
Usage
dpar_has_predictor(spec, lp)
gev_xi_chart_terms(fit)
gev_xi_chart_frame(frame, terms)
gev_xi_chart_start(fit, terms, pars)Details
gev_xi_chart_terms() lists each such xi: its response, linear
predictor key, parameter component and index, the fit's link, and
blocked, the reasons the chart cannot be used (a cens() or
trunc() term, whose CDF the chart does not carry, a second GEV
response, which would share the REPORTed name, or a mixture()
component, whose xi1, xi2, ... the chart does not map).
gev_xi_chart_frame()
returns the frame with each unblocked one in the tmp_xi chart, and
gev_xi_chart_start() carries a parameter list's xi coefficients
to tmp_xi at the fit's mu and sigma. dpar_has_predictor()
tells xi ~ 1, which brms samples on log1p, from no formula.