aug_spline_x_perturb — Spline-based x-axis perturbation

Group: Augmentation · C ABI: n4m_augmentation_spline_x_perturbations_*

Description

Spline x-axis perturbation augmenter.

Parameters

Name

Type

Default

spline_degree

int

3

perturbation_density

float

0.05

perturbation_range_min

float

-0.1

perturbation_range_max

float

0.1

rng

Optional[PCG64]

None

seed

int

0

API and bindings

C ABI (ABI 2): n4m_augmentation_spline_x_perturbations_apply · n4m_augmentation_spline_x_perturbations_create · n4m_augmentation_spline_x_perturbations_destroy. Use the linked public header for the exact signature, configuration, and result handles.

Python (verified public re-export):

from n4m.augmentation.splines import SplineXPerturbationAugmenter

Source signature: SplineXPerturbationAugmenter(spline_degree: int = 3, perturbation_density: float = 0.05, perturbation_range_min: float = -0.1, perturbation_range_max: float = 0.1, rng: Optional[PCG64] = None, seed: int = 0).

R: no current source-verified entry point was found for this catalog method.

MATLAB / Octave: no current source-verified entry point was found for this catalog method.

Explanations

Bibliographic source

No canonical paper defines this random x-grid perturbation. The native implementation is a parity-oriented analogue of SciPy spline resampling.

Mathematical principle

Fit a not-a-knot cubic B-spline to each row. Set the number of equally spaced perturbation anchors to \(\max[2,\operatorname{round}((p+4)d)]\), where d is perturbation_density; draw an offset at each anchor from perturbation_range_min to perturbation_range_max, linearly interpolate those offsets onto the spline knot vector, perturb the knots, and evaluate the altered spline on the original channel grid.

Appropriate uses

Robustness to sparse wavelength-registration errors with smooth interpolation between points.

Limits and validation

Only spline_degree=3 is accepted by the native constructor. Perturbed knots can become poorly ordered at excessive ranges; cubic evaluation can overshoot, and channel coordinates rather than physical wavelengths drive this API.

Implementation

Python role API n4m.augmentation.splines.SplineXPerturbationAugmenter; ABI 2 family n4m_augmentation_spline_x_perturbations_{create,apply,destroy}.

The ABI-2 implementation is the n4m_augmentation_spline_x_perturbations_* lifecycle in libn4m.

Sources and provenance

https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/core/augmentation/splines/spline_x_perturbations.h

See also: methods index · interactive dashboard