Enum TrustRegionDecision 

pub enum TrustRegionDecision {
    GrowAtBoundary,
    HoldInside,
    HoldModerate,
    ShrinkOnMarginalAccept,
    ShrinkOnRejection,
    RejectFloor,
}

Rich classification of the branch a TrustRegionPolicy::update took on a single trust-region step. Surfaced so callers can log at a glance whether the solver is being throttled by the region (ShrinkOnRejection / RejectFloor), sitting well inside it (HoldInside), or expanding into freshly available room (GrowAtBoundary).

The four Accepted-family variants (GrowAtBoundary, HoldInside, HoldModerate, ShrinkOnMarginalAccept) all correspond to accepted steps; the remaining two to rejected ones. Two orthogonal signals — whether the realized reduction was within the objective’s round-off noise floor, and whether the model’s predicted reduction was non-positive — are reported as booleans on TrustRegionStep rather than stealing a decision label, so the classification above stays a faithful superset of every consumer’s existing telemetry.

Variants

GrowAtBoundary

rho > eta_expand AND the step reached the region boundary — the model is excellent and the radius was the binding constraint, so the radius was expanded.

HoldInside

rho > eta_expand but the step sits inside the region; radius held (no evidence the region constrained the step).

HoldModerate

eta_shrink <= rho <= eta_expand (moderate fidelity) — radius held.

ShrinkOnMarginalAccept

Step accepted (rho > eta_accept) but rho < eta_shrink; radius shrunk to be more conservative next iteration.

ShrinkOnRejection

Step rejected — radius shrunk (and, when a rejection step cap is configured, additionally capped to a fraction of the proposed step norm so a re-proposal stays inside the rejected region).

RejectFloor

A shrink landed the radius at (or below) min_radius. Persistent RejectFloor is the unambiguous signal that no descent direction exists at the smallest admissible radius.

Implementations

impl TrustRegionDecision

pub fn label(self) -> &'static str

Stable, lower-snake-case label for structured logs.

pub fn is_accepted(self) -> bool

true for the decisions that correspond to an accepted step.

Trait Implementations

impl Clone for TrustRegionDecision

fn clone(&self) -> TrustRegionDecision

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for TrustRegionDecision

impl Debug for TrustRegionDecision

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for TrustRegionDecision

impl PartialEq for TrustRegionDecision

fn eq(&self, other: &TrustRegionDecision) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for TrustRegionDecision