Experiments and data¶

An experiment describes the measurement and the model used to calculate it. For powder diffraction, that includes instrument and peak-profile settings, background, exclusions and linked structures.

The shared Experiment chapter explains the scientific model; the steps below describe this interface.

Inspect a project¶

import edi

project = edi.Project.load('path/to/project')

for experiment in project.experiments:
    print(experiment.name)

Keep experimental settings with the measurement they describe. Structural parameters belong to a structure, while wavelength and zero shift and profile parameters belong to the experiment model.

Read a measured powder pattern¶

For a loaded powder experiment, its data exposes measured intensities and their uncertainties. After a calculation it also carries the calculated intensities:

project.analysis.calculate()

for experiment in project.experiments:
    pattern = experiment.data
    if pattern is not None:
        print(experiment.name, len(pattern.intensity_calc))

This snippet is limited to the powder-pattern data view. Single-crystal experiments carry reflections and require the corresponding reflection API.

Construct an experiment from a data file¶

For a constant-wavelength neutron powder measurement:

experiment = edi.ExperimentFactory.from_data_path(
    name='measurement',
    data_path='measurement.xye',
    sample_form='powder',
    beam_mode='constant wavelength',
    radiation_probe='neutron',
)

The powder reader accepts plain x y or x y sigma rows, separated by whitespace or commas. It skips nonnumeric lines, estimates uncertainty when omitted, drops nonpositive intensities, sorts the axis and keeps the first repeated-axis point. Review the resulting data when converting an unfamiliar file.

The factory creates the experiment and reads its data. You still need to choose its instrument/profile settings and link a structure before treating it as a complete model.

Read an experiment from CIF¶

experiment = edi.ExperimentFactory.from_cif_path('experiment.cif')
project.experiments.add_from_cif_path('experiment.cif')

Both read a CIF or .edi file with the experiment's type, instrument, peak profile, background, excluded regions, linked structures and measured points. from_cif_str and add_from_cif_str take the text instead. An experiment added to a project must link structures the project holds; otherwise the import is refused and the project is left as it was. Imported values start fixed, and items EasyDiffraction does not read come back as warnings. See CIF files.

experiment.instrument.facility and experiment.instrument.name say where the measurement was made, ? when unknown. experiment.experiment_type.dimensionality is 1d, and experiment.experiment_type.polarisation is unpolarised for neutrons and . for X-rays; each accepts only that value.

Measured data or a simulation range¶

A measured pattern supports comparison and fitting. A simulation range supports a forward calculation without observations. A project can contain both kinds; fitting uses experiments with measured data.

Read calculate a pattern or load and fit for the next step.