Checks whether a Gaussian candidate law can reach a positive-weight event for almost every retained latent context. The complete candidate-plus-retained covariance must be positive definite. Retained covariance itself may be singular. This is a support check, not a numerical integration diagnostic.

selection_event_support(prior, candidate_basis)

Arguments

prior

a weightfunction prior specifying one publication group's rule.

candidate_basis

finite numeric matrix whose column space is exactly the candidate variation in that group. Zero columns are allowed, including a matrix with no columns. Use compiler-declared source geometry, not posterior covariance estimates or numerical rank truncation.

Value

A list with feasible (TRUE, FALSE, or NA) and a stable character reason. FALSE proves that some positive-probability retained contexts have zero acceptance probability. NA means that a positive direction could not be certified. Reasons are positive_weights, varying_best_result, varying_two_tails, positive_direction, deterministic_candidate, deterministic_candidate_rows, opposed_candidate_direction, or positive_direction_unavailable.

Details

Positive weights require no candidate variation. With hard-zero bins, the best-result rule needs at least one varying result. Two-sided product selection, and one-sided product selection with a positive least-significant weight, need every result to vary. One-sided product selection with a zero least-significant weight instead needs a strictly positive vector in the candidate column space.

The positive-direction check uses sign-definite columns, then base-R QR and optimization as candidate finders. A computed direction is accepted only when its positive entries exceed a standard dot-product roundoff bound. Failed searches return unknown rather than proving infeasibility.

The caller must check every candidate span having positive prior probability, including zero-SD and inclusion branches. When only a guaranteed subspace is supplied, only a positive result is conclusive; other results cannot classify the complete candidate law. This helper does not derive scale guarantees or change weights, priors, or source geometry.