Chandra Announcement: Release of the Sherpa 4.18.0 package for Python

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Tara Gokas

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Oct 7, 2025, 12:50:38 PMOct 7
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Release of the Sherpa 4.18.0 package for Python


The Sherpa 4.18.0 modeling and fitting package for Python for general usage outside of the CIAO environment was released on October 7, 2025. This release is compatible with Python versions 3.10 to 3.13. Note that the paper describing Sherpa was published last year in the Astrophysical Journal Supplement Series and provides a good reference to the package.

This release of Sherpa includes enhancements, documentation changes, infrastructure changes, and bug fixes. Highlights include:

New features

  • Added support for using optimizers from SciPy and Optimagic (#2303)

  • Add a version of the CStat statistic (“cstatnegativepenalty”) that can be used if a model can predict negative values (#2294)

  • Allow multiple datasets to be plotted with a single call (#1712, #2328)

Enhancements

  • Provide easy access to the parameter values tried during a fit (#2315)

  • Add support for XSPEC 12.14.1 and 12.15.0 (#2116, #2252)

  • The interface to the XSPEC models has been simplified to make it more closely resemble XSPEC for additive models (#2275)

Bug fixes

  • Always calculate the covariance matrix when using get_draws and eqwidth, and ensure the correct dataset identifiers are used (#2374)

  • Improve the output of save_all for PHA data, in particular when using PHA2 data (#2377, #2382)

  • Ensure backend-specific (e.g. matplotlib or bokeh) plotting options can be used (#2371)

  • The sampling routines has seen updates related to the choice of the Random Number Generator (#2331), handling of linked parameters (#2333), the clipping of parameters (#2336)

Deprecations

  • The sigma parameter has been renamed to scale for normal_sample (#2211)

  • XSPEC table models must now be loaded via load_xstable_model and not load_table_model (#2352)

  • Remove support for XSPEC 12.12.0 and 12.12.1 (#2329)


For detailed Release Notes go to https://github.com/sherpa/sherpa/releases/tag/4.18

For documentation and installation instructions go to https://sherpa.readthedocs.io/en/latest/

Information on recent releases and citation information is available using the Digital Object Identifier (DOI) https://zenodo.org/records/17288983




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