Mark an outer-grid setting as a default rather than a pin

Declares that a setting shaping the outer hyperparameter grid carries a default the caller computed, not a choice the user made. The auto-recenter pass (outer_grid_placement) leaves a user-pinned setting exactly as given, and re-centres (or, for a prior, engages its own regularizer over) a marked one when the fit rails against its ceiling.

Four kinds of setting take the mark:

a grid axis on a nested-Laplace prior block (sigma_grid, tau_grid, ...) – a numeric vector of nodes, or the [n_cells x k] matrix of pre-paired coordinates the families whose axis is a matrix take (mcar / miid's logchol_grid, tgmrf's theta_grid_built);
an entry of tulpa_nested_laplace_joint()'s phi_grid – one arm's dispersion axis;
a scalar grid-construction knob in control, for a driver that builds its axes rather than taking them (fit_st_nested()'s n_grid_spatial, tau_upper, ...);
a prior_sigma hyperprior specification – a list, e.g. list("pc.prec", c(U = 3, alpha = 0.01)).

Wrapper packages are the intended caller: one that builds a default of its own – because it derives a second axis from it, hands the same vector to several blocks, or exposes its own argument with a default – would otherwise be indistinguishable from a user who pinned that setting deliberately. Mark it and the rescue stays live. A setting whose value is exactly the engine's own default is recognised without a mark; anything else needs one – and a dispersion axis ALWAYS needs one, since the engine has no default of its own to recognise it against.

The mark is an attribute, so it is dropped by sort(), [, c() and as.numeric(): build the value first, mark it last.

Usage

auto_grid(x, place = TRUE)

Arguments

x: Numeric vector or matrix of grid nodes, a numeric scalar knob, or a prior-specification list.
place: May the auto-placement pass move this axis onto its own posterior? TRUE (default) declares a default the engine may re-place; FALSE declares one it must integrate as written.

Value

x carrying the marker attribute. Numeric input is coerced to double IN PLACE, so everything else it carries – dim() and dimnames() above all – survives the mark; a list is returned unchanged apart from the attribute.

Declaring a default the engine must integrate as written

place = FALSE separates the two questions the mark otherwise answers at once. Provenance – whose choice these nodes are – and placement policy – whether the pass may move them – are different questions, and a package that measured its own default as the one to integrate has an answer to the second that is not "the user pinned it". Such an axis is treated exactly as a pin everywhere the engine ACTS on it (the placement pass leaves it, refinement densifies within its span rather than following the posterior past the end nodes, and no curvature is computed for it), and differs only in what the fit REPORTS: "default_axis_pinned" rather than "axis_pinned", so a reader is not told they pinned an axis they never wrote down. Leaving the mark off instead buys the same integration and says the wrong thing about it.

place is read wherever the engine would otherwise RE-PLACE the setting: a grid axis, and a scalar grid-construction knob. A prior_sigma specification is not re-placed but replaced, by the engine's own regularizer, and carries no place.

Examples

prior <- list(type = "icar", sigma_grid = auto_grid(c(0.1, 0.5, 1, 2, 3)))
is_auto_grid(prior$sigma_grid)
is_auto_grid(auto_grid(list("pc.prec", c(U = 3, alpha = 0.01))))
auto_grid_place(auto_grid(c(0.5, 1, 2), place = FALSE))