rexafs 0.2.5

Rust-powered X-ray absorption spectroscopy analysis and EXAFS fitting
Documentation

rexafs for Rust

Published user guide · Versioned API reference

Rust-powered X-ray absorption analysis, developed under the codename xraytsubaki. The core includes normalization, AUTOBK, Fourier transforms, group processing, EXAFS fitting, structure handling, LCF/PCA and spectrum tools.

Install the library with cargo add rexafs. In this checkout, run cargo test -p rexafs to exercise the core regression suite.

Start with a spectrum

use rexafs::{io, Spectrum};
let mut spectrum = io::read_qas_transmission("scan.dat")?;
spectrum.fft()?;
assert_eq!(spectrum.k().unwrap().len(), spectrum.chi().unwrap().len());
// For your own data: Spectrum::from_arrays(&energy, &mu)?;
# Ok::<(), Box<dyn std::error::Error>>(())

fft() calculates missing normalization and background results using the selected methods and defaults. normalize(), calc_background(), fft() and ifft() also support explicit chaining. The same stage names are used in Python and TypeScript. There is no separate process() facade.

Configure methods with NormalizationMethod, BackgroundMethod, PrePostEdge, AUTOBK, XrayFFTF and XrayFFTR (the inverse-transform settings). In 0.2.5 and later, pass settings directly:

use rexafs::{AUTOBK, PrePostEdge, Spectrum};
# let energy = [1.0, 2.0, 3.0];
# let mu = [0.0, 0.5, 1.0];
let mut spectrum = Spectrum::from_arrays(&energy, &mu)?;
let mut background = AUTOBK::new();
background.rbkg = Some(1.2); // Low-R background cutoff, in angstroms.
spectrum.set_normalization_method(PrePostEdge::new())?;
spectrum.set_background_method(background)?;
# Ok::<(), rexafs::Error>(())

Rust setters move configurations into the spectrum; clone a reusable setting explicitly. Version 0.2.4 uses Some(BackgroundMethod::AUTOBK(background)) and Some(NormalizationMethod::PrePostEdge(parameters)). Those forms and None for default settings remain supported. Setters invalidate dependent results. Alternative methods remain selectable; unimplemented methods return explicit errors. Inputs to from_arrays must be finite, equal-length arrays with strictly increasing energy in eV. k(), chi() and chir() borrow stored buffers; the other public array getters return owned copies. A getter returns None when its result is unavailable and never computes it implicitly.

See the API guide for examples, units and ownership. Spectrum and Group remain aliases for XASSpectrum and XASGroup.

What the calculations mean

Normalization subtracts a fitted pre-edge baseline and divides absorption by its edge step. AUTOBK estimates the smooth background to obtain the EXAFS oscillations, chi(k). The Fourier transform weights and windows those oscillations to display them against R; its peaks are not automatically phase-corrected bond lengths. An inverse transform filters selected R contributions back into q space.

The processing theory guide explains the equations, symbols, units, assumptions and implementation choices, with scientific references. Use the fitting-statistics guide when interpreting structural fits and uncertainties.

Features and scope

  • Default trust-region: optional fitting solver support.
  • refeff-runner: ReFEFF's Rust EXAFS engine, with path outputs for fitting.
  • feff10-runner: the FEFF10 backend through the feff10 dependency.
  • plotting: core plot builders through ruviz.
  • amcsd, materials-project, cod: optional structure sources.
  • ndarray-compat: legacy ndarray calculation path; the default is nalgebra.

Existing FEFF path files can be fitted without compiling a calculation backend. FeffFit and the fitting module support single and joint datasets, independent batches and k/R/q fit spaces. FeffFlavor::Feff10 parsing is still separate from FEFF10 execution; see the historical compatibility notes in the repository. The native core has broader APIs than the Python and JavaScript bindings.

Licensed under MIT OR Apache-2.0; dependency and fixture notices remain applicable.

Plotting (Feature-Gated)

Core plotting is available behind the plotting feature using ruviz. The complete plot_demo also runs external FEFF85L modules. Install the FEFF binaries supplied with XrayLarch and set REXAFS_FEFF8L_RDINP to the path of feff8l_rdinp if the example cannot discover it. The plotting builders themselves do not require that executable when plotting existing spectra or fit results.

cargo run -p rexafs --features plotting --example plot_demo

On Apple Silicon, if your linker resolution requires an explicit target linker:

CARGO_TARGET_AARCH64_APPLE_DARWIN_LINKER=clang cargo run -p rexafs --features plotting --example plot_demo

plot_demo writes outputs to:

  • crates/rexafs/target/plot_demo

plot_demo coverage:

  • FEFF85L module runs from full feff.inp: Co, FeO_withPb, MnO2, ZnSe
  • Real fitting via FeffFit::fit(): Cu, ZnSe
  • Fit plots per material: k, k + window, r, r + window range

To regenerate Cu/ZnSe fit references directly from XrayLarch:

uv run --with xraylarch python crates/rexafs/scripts/generate_larch_fit_references.py

FEFF fit compatibility is regression-tested against these regenerated Cu/ZnSe fixtures:

  • compared fields: amp, de0, sig2, dr values and stderr
  • compared stats: chi_square, reduced_chi_square, n_idp, r_factor
  • tolerance policy: relative tolerance 20% with absolute fallback 1e-8 (de0 value uses 0.2 eV absolute fallback near zero)

Important behavior

  • Plotting APIs are available through PlotXAS with a mutable entrypoint: plot(&mut self).
  • Plot text rendering uses typst(true) by default for scientific notation-friendly labels/ticks.
  • Plotting auto-computes missing intermediates when required:
    • mu() may call normalize() and renders flattened mu(E) by default
    • norm() may call normalize()
    • k() may call calc_background()
    • r() may call calc_background() and fft()
  • k() panels use symmetric y-limits (-y_lim..y_lim) and y-axis units derived from kweight.
  • FeffFitResult::plot().k() defaults to fit/dataset kweight unless .kweight(...) overrides it.
  • r() panels default to xlim(0.0, 6.0).
  • r() defaults to magnitude traces. Calling .real() and/or .imag() switches to those components unless .mag() is also included (e.g. .r().mag().real().imag()).
  • FeffFitResult::plot().r() includes path |chi(R)| traces when magnitude is active.
  • Window overlays are disabled by default.
  • .window(true) is an alias that enables both .window_fn(true) and .window_box(true) for k() panels.
  • .window_fn(...) is supported only on k() panels.
  • .window_box(...) is supported on k() panels, and on r() panels for FeffFitResult plots; it renders two range markers (min/max), not a rectangle.
  • FeffFitResult now includes varying_names, covariance, and correlation (matrix order follows varying_names).
  • save_png() combines multiple panels. to_svg() and render_plot() require a single panel; to_svg_panels() returns a separate SVG string for each panel.

XASSpectrum examples

use rexafs::prelude::*;
use rexafs::xafs::io::load_spectrum_QAS_trans;

let path = format!("{}/tests/testfiles/Ru_QAS.dat", env!("CARGO_MANIFEST_DIR"));
let mut spectrum = load_spectrum_QAS_trans(path)?;

spectrum.plot().mu().save_png("flat_mu.png")?;
spectrum.plot().norm().edges(true).save_png("norm_edges.png")?;
spectrum.plot().k().kweight(2.0).window(true).save_png("chi_k.png")?;
spectrum.plot().r().save_png("chi_r_mag.png")?;
spectrum.plot().r().real().save_png("chi_r_real.png")?;
spectrum.plot().r().mag().real().imag().save_png("chi_r_all.png")?;

spectrum
    .plot()
    .mu()
    .norm()
    .k()
    .r()
    .title("overview")
    .save_png("overview.png")?;
# Ok::<(), Box<dyn std::error::Error>>(())

XASGroup examples

use rexafs::prelude::*;

let mut group = XASGroup::new();
// populate group.spectra ...

group.plot().mu().save_png("group_overlay.png")?;
group.plot().mu().select(&[0, 2]).save_png("group_selected.png")?;
group.plot().mu().stacked(0.25).save_png("group_stacked.png")?;
# Ok::<(), Box<dyn std::error::Error>>(())

FeffFitResult examples

use rexafs::prelude::*;

let mut fit = FeffFitResult::default();
// populate fit result vectors or datasets ...

fit.plot().k().save_png("fit_k.png")?; // uses fit kweight by default
fit.plot().k().window(true).save_png("fit_k_window.png")?; // with window
fit.plot().r().save_png("fit_r.png")?; // includes path |chi(R)| traces
fit.plot().r().window_box(true).save_png("fit_r_window.png")?; // with range markers
fit.plot().r().real().save_png("fit_r_real.png")?;
fit.plot().r().mag().real().imag().save_png("fit_r_all.png")?;
fit.plot().k().dataset(0).save_png("fit_dataset0_k.png")?;
# Ok::<(), Box<dyn std::error::Error>>(())