Demo datasets#

The repository ships six simulated neutron reflectometry files for trying out the constraint and multiple-contrast features described in material and model setup. They live in examples/datasets, together with a full write-up of each demo and the script that regenerates them.

All six are ORSO .ort files simulated from a known structure with 4 % noise and 5 % dQ/Q resolution, so every demo has a right answer to compare the fit against. The ground truth is recorded in each file’s header, and each header also carries the sample structure in the ORSO model language, so the files can be opened in two ways:

Model › Load a sample › Load sample from file builds the layer stack for you, with the true thicknesses, roughnesses and SLDs as starting values. Change those starting values before fitting, so there is something to find.
Experiment › Load experiment(s) from file(s) loads the reflectivity curve, which also works with a hand-built sample.

Dataset	Demonstrates
`two_layer_film.ort`	A two-layer film whose total thickness is known (exactly 90 Å) - the thickness budget and the derived total film thickness.
`swapped_layers.ort`	A layer-ordering inequality: started from the swapped guess, the fit only recovers the truth with a `≤` constraint between the two thicknesses.
`ni_ti_multilayer.ort`	A `[Ti / Ni] × 8` repeating multilayer with a Bragg peak that pins the period - the Constant period Λ and Conformal roughness recipes.
`dppc_monolayer.ort`	A DPPC monolayer at the air/D2O interface - the surfactant recipes (equal head/tail area per molecule, solvent roughness).
`film_contrasts.ort`	Three contrasts (D2O, H2O, CMSi) of a film on silicon in one file. Each dataset carries its exact slab model, so Load sample from file builds the D2O model. It demonstrates Add contrast, pairing experiments with models, per-contrast scale and background, and a joint fit, and in a variant Link contrasts for a contrast built as a separate model. Start here for multiple contrasts.
`dppc_contrasts.ort`	Three contrasts of one DPPC monolayer in one file (d-DPPC on D2O, d-DPPC on air-contrast-matched water, h-DPPC on D2O). It demonstrates Add contrast, pairing experiments with models, and a joint fit that separates head hydration from head thickness, which no single contrast can do.

Note

For ni_ti_multilayer.ort the loaded stack arrives flattened (8 × [Ti | Ni] becomes 16 layers in one assembly); rebuild it as a Repeating Multi-layer by hand for the constant-period demo. For dppc_monolayer.ort the loaded stack is the slab equivalent of the surfactant; replace it with a Surfactant layer assembly for the surfactant recipes. dppc_contrasts.ort has no sample model in its header (the import builds plain slabs only, not a solvated monolayer): build the reference contrast by hand and derive the other two with Add contrast.