[Neutron] New release of McStas/McXtrace, v3.8.4

[Peter Kjær Willendrup]

September 11th, 2026: McStas and McXtrace 3.8.4 released
Installation

  *   For McStas proceed to the McStas install docs (GitHub)<https://github.com/mccode-dev/McCode/blob/main/INSTALL-McStas/README.md>
  *   For McXtrace proceed to the McXtrace install docs (GitHub)<https://github.com/mccode-dev/McCode/blob/main/INSTALL-McXtrace/README.md>

Changes in McStas/McXtrace 3.8.4

Covers everything since the last full release, 3.7.9 (July 2, 2026), including all changes already shipped quietly via the intermediate conda-forge releases 3.7.10–3.8.3, and a ground-up rewrite of the McStas/McXtrace manuals.

Sorry for any incovenience caused if you installed any of 3.8.1-3... Some doc-details were still not in place!

What's Changed - highlights

  *   For a full description of all release content, please visit the project websites or GitHub!

Common to McStas and McXtrace
Manuals

  *   First full manual makeover since the McStas 2.x / McXtrace 1.x series. T
  *   AI-assisted: reference material and source code (usage articles, grammar/cogen.c, example instruments, component sources, tool CLIs) were given to an AI coding agent to draft the updated text. Given the scale of the rewrite, minor errors/omissions in the manuals are expected — please flag anything you spot via a GitHub issue
  *   mcdoc's browser-based overview page now also links to per-tool cheat-sheets new standalone Instrument/Component grammar reference pages, all a click away from the component browser.

New tooling

  *   New  - and updated user tools:
     *   mcrun/mxrun: improved multi-dimensional scan-modes and single-file output when scanning to HDF5/NeXus format
     *   mcplot/mxplot-matplotlib: improvement to presentation and performance
     *   New mcplot-derived tools (for pyqtgraph, matplotlib and HTML output formats)
        *   mcplotdiff/mxplotdiff for plotting differences between two datasets
        *   mccoplot/mxcoplot for plotting 1D datasets together for comparison

Code generator, grammar, project infrastructure

  *   Fixes:
     *   RNG correctness fix in presence of SPLIT @mads-bertelsen
     *   Restored option to run with Mersenne Twister on CPU @mads-bertelsen
     *   Add input parameters to base .py instrument @MilanKlausz
  *   Grammar simplification:
     *   COPY(instance) to no longer transfers EXTEND and other advanced attributes
  *   Increased compatibility with mcstas-antlr
  *   Various improvements to CI - including systematic testing against mcstas-antlr

McStas only

  *   New instrument:
     *   import of FRMII_SPODI / FRMII_SPODI_MULTI, from MLZ Garching from @kinetik161 et. al.
  *   New instruments:
     *   import of 3 x imaging instruments from various sources (PSI_ICON, Radiography_Lithium_Battery, Radiography_Sword)
  *   New included library mcstas-chopper-lib, from @g5t
     *   Components Masked_ESS_butterfly and NXdisk_chopper,
     *   instruments Masked_ESS_butterfly_image, NXdisk_chopper_display and NXdisk_chopper_image.
     *   All fully integrated with McStas
  *   Various fixes and improvements

McXtrace only

  *   Various fixes and improvements to components/instruments

New Contributors

  *   @kinetik161 made their first contribution in #2608
  *   @mads-bertelsen-agentic made their first contribution in #2624
  *   @MilanKlausz made their first contribution in #2638

All the best on behalf of the McStas-McXtrace team,

Peter Kjær Willendrup
Forskningsingeniør, Specialkonsulent

DTU Physics

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Technical University of Denmark


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Department of Physics
Fysikvej
Building 307
DK-2800 Kongens Lyngby

Main office at
ESS DMSC
Building 305
DK-2800 Kongens Lyngby

Direct +45 2125 4612
Mobil +45 2125 4612
Fax +45 4593 2399
pkwi at fysik.dtu.dk

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