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[ESSSANS] docs: compute reference curve instead of reading it from file #694

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[ESSSANS] docs: compute reference curve instead of reading it from file #694

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docs: compute reference curve instead of reading it from file
jokasimr Aug 6, 2026
935a712
fix
jokasimr Aug 6, 2026
94e6859
Merge branch 'main' into compute-polygauss
jokasimr Aug 7, 2026
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2 changes: 1 addition & 1 deletion packages/esssans/docs/user-guide/loki/loki-direct-beam.ipynb
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Original file line number Diff line number Diff line change
Expand Up @@ -247,7 +247,7 @@
"source": [
"from scipp.scipy.interpolate import interp1d\n",
"\n",
"Iq_theory = sc.io.load_hdf5(loki.data.loki_tutorial_poly_gauss_I0())\n",
"Iq_theory = loki.data.loki_tutorial_poly_gauss_I0_data()\n",
"f = interp1d(Iq_theory, 'Q')\n",
"I0 = f(sc.midpoints(workflow.compute(QBins))).data[0]\n",
"I0"
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27 changes: 27 additions & 0 deletions packages/esssans/src/ess/loki/data.py
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Expand Up @@ -2,6 +2,8 @@
# Copyright (c) 2023 Scipp contributors (https://github.com/scipp)
from pathlib import Path

import numpy as np
import scipp as sc
from ess.sans.types import (
BackgroundRun,
DirectBeamFilename,
Expand Down Expand Up @@ -164,6 +166,31 @@ def loki_tutorial_poly_gauss_I0() -> Path:
return Path(_registry.get_path('PolyGauss_I0-50_Rg-60.h5'))


def loki_tutorial_poly_gauss_I0_data() -> sc.DataArray:
"""Return the analytical I(Q) model for the tutorial Poly-Gauss sample.

The model is the SasView ``poly_gauss_coil`` model with an intensity at zero
Q of 50, a radius of gyration of 60 angstrom, a polydispersity of 1.02, and
a background of 0.2.
Comment on lines +172 to +174

@nvaytet nvaytet Aug 6, 2026

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I think the function would be more useful if all the parameters would be values we can tune?
You can still give them the default values you list here, but it would make it useful in case we want a new intensity at Q=0, different Q range, etc..

@SimonHeybrock SimonHeybrock Aug 7, 2026 •
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Yes, the goal of the issue was to make the computation part of a production code (not just a tutorial helper function), i.e., a graph node computing the model. I don't know if the params should all be workflow params, check with Judidth.

"""
q = sc.geomspace(
dim='Q',
start=0.0005237261180003165,
stop=0.5,
num=150,
unit='1/angstrom',
)
radius_of_gyration = sc.scalar(60.0, unit='angstrom')
# Preserve the float32 parameter values used to compute the original reference.
polydispersity = float(np.float32(1.02))
background = float(np.float32(0.2))

u = polydispersity - 1.0
z = (q * radius_of_gyration) ** 2 / (1.0 + 2.0 * u)
form_factor = 2.0 * ((1.0 + u * z) ** (-1.0 / u) + z - 1.0) / ((1.0 + u) * z**2)
return sc.DataArray(50.0 * form_factor + background, coords={'Q': q})


def loki_tutorial_direct_beam_all_pixels() -> DirectBeamFilename:
"""File containing direct beam function computed using the direct beam iterations
notebook, summing all pixels."""
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2 changes: 1 addition & 1 deletion packages/esssans/tests/loki/directbeam_test.py
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Expand Up @@ -14,7 +14,7 @@


def _get_I0(qbins: sc.Variable) -> sc.Variable:
Iq_theory = sc.io.load_hdf5(loki.data.loki_tutorial_poly_gauss_I0())
Iq_theory = loki.data.loki_tutorial_poly_gauss_I0_data()
f = interp1d(Iq_theory, 'Q')
return f(sc.midpoints(qbins)).data[0]

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