pp_first_derivative — Shape-preserving first numerical derivative¶
Group: Preprocessing · C ABI: n4m_transform_first_derivative_*
Description¶
np.gradient(X, delta, axis=1, edge_order=...) (shape-preserving).
Parameters¶
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API and bindings¶
C ABI (ABI 2): n4m_transform_first_derivative_create · n4m_transform_first_derivative_destroy · n4m_transform_first_derivative_transform. Use the linked public header for the exact signature, configuration, and result handles.
Python (verified public re-export):
from n4m.transform.smoothing import FirstDerivative
Source signature: FirstDerivative(delta: float = 1.0, edge_order: int = 2).
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 unique paper defines numpy.gradient; the spectroscopic use of derivatives is discussed by Norris & Williams (1984), Optimization of mathematical treatments of raw near-infrared signal.
Mathematical principle¶
The operator reproduces a first numpy.gradient pass along each row: centered differences inside and one-sided formulas of edge order one or two at boundaries, all divided by delta. Output shape equals input shape.
Appropriate uses¶
Suppressing constant offsets and sharpening overlapping bands when retaining the original number of channels is useful.
Limits and validation¶
It amplifies noise and assumes uniform channel spacing. Boundary samples use different stencils, and edge_order=2 needs enough wavelengths.
Implementation¶
n4m.transform.smoothing.FirstDerivative wraps n4m_transform_first_derivative_*; stencils are in preprocessing/derivatives/first_derivative.c.
The ABI-2 implementation is the n4m_transform_first_derivative_* lifecycle in libn4m.
Sources and provenance¶
https://github.com/GBeurier/nirs4all-methods/blob/main/cpp/src/core/preprocessing/derivatives/first_derivative.c; https://numpy.org/doc/stable/reference/generated/numpy.gradient.html
See also: methods index · interactive dashboard