Struct OuterGradientFdComponent 

pub struct OuterGradientFdComponent {
    pub block: String,
    pub index: usize,
    pub analytic: f64,
    pub fd: f64,
    pub fd_refined: Option<f64>,
}

Per-θ component of an outer-gradient finite-difference audit.

Fields

block: String

Human label for the block this coordinate belongs to (e.g. “timewiggle”).

index: usize

Flat θ index.

analytic: f64

Analytic ∂V/∂θ_i returned by the family evaluator.

fd: f64

Second-order central finite-difference of the outer criterion in θ_i at the coarse step h. Its leading error is O(h²)·V''', which is large on a steeply-curved coordinate (e.g. the Matérn log-κ axis, whose operator penalty scales like κ^{2m}, m = ν + d/2).

fd_refined: Option<f64>

Richardson 4th-order refinement of fd, combining the h and h/2 central differences to cancel the leading O(h²) truncation term (residual O(h⁴)). Populated ONLY when the coarse fd gap looks like it might trip the DESYNC band, so clean coordinates stay cheap (2 evals); suspicious ones pay 2 extra evals to tell genuine derivative error (h-independent gap) apart from pure FD truncation (h²-shrinking gap).

Implementations

impl OuterGradientFdComponent

pub fn best_fd(&self) -> f64

The FD estimate that best matches the analytic gradient — the Richardson-refined value when it is closer, else the coarse fd.

Picking the closer of the two is deliberately CONSERVATIVE for the desync verdict: a true derivative bug makes the analytic gradient differ from the true derivative by an h-independent amount, so BOTH the coarse and the refined FD (each converging to that true derivative) stay far from it — the min gap remains large and DESYNC still fires. Only a truncation-dominated gap (where refinement recovers the true derivative) collapses, which is exactly the case that must NOT be flagged. So abs_gap can only shrink vs the coarse-only value: no previously-passing audit can regress.

pub fn abs_gap(&self) -> f64

Absolute analytic−FD gap against the best available FD estimate.

pub fn ratio(&self) -> Option<f64>

analytic/fd ratio (None when fd≈0). A clean −1 signals a sign convention; a stable constant ≠1 signals a dropped/extra additive term.

Trait Implementations

impl Clone for OuterGradientFdComponent

fn clone(&self) -> OuterGradientFdComponent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for OuterGradientFdComponent

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

Formats the value using the given formatter.