# rietx at a glance This page says which data rietx fits, what it calculates, and what each feature has been checked against. A row without a comparison with another code says so, and gives what it was checked against instead. The [validation page](validation.html.md) has the numbers behind each link. ## Data rietx fits rietx fits powder patterns measured with X-rays or with constant-wavelength neutrons. Each instrument preset sets the geometry and the radiation: | Preset | Instrument | |---|---| | `Instrument.bragg_brentano` | laboratory X-ray, flat plate | | `Instrument.debye_scherrer` | X-ray in a capillary, including synchrotron | | `Instrument.flat_plate_transmission` | X-ray, flat plate in transmission | | `Instrument.constant_wavelength_neutron` | neutron, one wavelength | A joint fit refines several patterns of one specimen together, such as a synchrotron pattern and a neutron one. The structure is shared, and each pattern keeps its own instrument, wavelength and background. A joint fit shares the crystallite size and scales each pattern’s width in degrees by its wavelength. `refine_sequential` fits a series of patterns one after another, each starting from the last answer. [About a fit](../concepts/fit.html.md) follows one fit through its stages. Neutron time of flight is not refined. `Instrument.tof_neutron_bank` builds a bank and the readers open one, and a time-of-flight fit is refused by name. The [roadmap](roadmap.html.md) lists it among the work fenced for a 2.0 series. ## Features and what they were checked against | Feature | What rietx has | Checked against | Read more | |---|---|---|---| | Rietveld, laboratory X-ray | flat-plate, capillary and transmission geometry, with the Kα doublet | GSAS on [fluorapatite](validation.html.md#fluorapatite-against-gsas), a flat plate; the NIST [certificates](validation.html.md#against-a-certificate-or-a-weighed-composition) of LaB₆ and corundum | [About a fit](../concepts/fit.html.md), [calibrating an instrument](../guides/calibrate.html.md) | | Rietveld, synchrotron X-ray | multi-phase fits and a refinable wavelength | TOPAS on [LaB6 and cBN](validation.html.md#lab6-and-cbn-against-topas), TOPAS and GSAS-II on [two phases](validation.html.md#two-phases-against-topas-and-gsas-ii), XND on [silicon](validation.html.md#silicon-against-xnd) | [About a fit](../concepts/fit.html.md) | | Rietveld, constant-wavelength neutron | the same model with neutron scattering lengths | a [published refinement](validation.html.md#one-specimen-two-radiations), and TOPAS 6 on [calculated patterns](validation.html.md#calculated-patterns-against-topas-6) | [About a fit](../concepts/fit.html.md) | | Joint fit of several patterns | one structure, one instrument per pattern, a refinable wavelength | the [published combined refinement](validation.html.md#one-specimen-two-radiations) of one specimen | [Fitting an X-ray and a neutron pattern together](../guides/joint.html.md), [joint refinement](../reference/joint.html.md) | | Le Bail and Pawley | intensities refined per reflection, atoms held | rietx’s own Rietveld results, since no other code was compared | [About a fit](../concepts/fit.html.md) | | Peak shape and axial divergence | pseudo-Voigt (TCHZ) and Voigt, with Finger–Cox–Jephcoat axial divergence | TOPAS 6, on [calculated patterns](validation.html.md#calculated-patterns-against-topas-6) with the pseudo-Voigt | [About parameters](../concepts/parameters.html.md), [calibrating an instrument](../guides/calibrate.html.md) | | Anisotropic strain | Stephens’s model, with the allowed terms derived from the space group | TOPAS 6, on [calculated patterns](validation.html.md#calculated-patterns-against-topas-6) | [About parameters](../concepts/parameters.html.md) | | Background | Chebyshev, P-spline and declared humps | TOPAS 6, on [calculated patterns](validation.html.md#calculated-patterns-against-topas-6) with Chebyshev and P-spline backgrounds | [About parameters](../concepts/parameters.html.md#background), [adding a hump](../guides/hump.html.md) | | Extinction | Sabine extinction | TOPAS 6, on [calculated patterns](validation.html.md#calculated-patterns-against-topas-6) | [Parameter map](../reference/parameters.html.md) | | Texture | March–Dollase and spherical harmonics | spherical harmonics against [GSAS-II](validation.html.md#spherical-harmonic-texture-against-gsas-ii) | [Parameter map](../reference/parameters.html.md) | | Phase fractions | weight fractions with esds | the weighed compositions of the IUCr [round robin](validation.html.md#against-a-certificate-or-a-weighed-composition), and TOPAS on [LaB6 and cBN](validation.html.md#lab6-and-cbn-against-topas) | [Finding each phase’s weight fraction](../guides/qpa.html.md), [about correlations and esds](../concepts/correlations.html.md) | | Files from other programs | TOPAS `.inp`, FullProf `.pcr` and GSAS `.EXP` read in with their refine flags, and GSAS-II `.gpx` read in | the free set GSAS states in `FAP.EXP`, [rebuilt exactly](validation.html.md#fluorapatite-against-gsas) | [Opening another program’s refinement](../guides/foreign.html.md), [names in other programs](../reference/foreign-names.html.md) | Magnetic structures are in development. The pattern rietx calculates for a magnetic phase matches TOPAS 6’s on one [calculated pattern](validation.html.md#calculated-patterns-against-topas-6). A refined moment has no comparison with another code yet. The [roadmap](roadmap.html.md) lists the work. ## What the report adds Beside Rwp and the table of refined values, rietx returns a report of where the fit misses the data and what that misfit looks like, and a list of diagnostics. A diagnostic names a parameter that sits on a bound, two parameters the data cannot separate, or a phase the data cannot see. [About the report](../concepts/report.html.md) describes the three layers. Each refinement stage is also kept as a node in a history, so a stage can be restored and the plan forked.