Welcome to Astromodels’s documentation!

About astromodels

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Astromodels is a very flexible framework to define models for likelihood or Bayesian analysis of astrophysical data.

Even though it has been designed having in mind analysis in the spectral domain, it can be used also as a toolbox containing functions of any variable.

Astromodels is not a modeling package, it only gives you the tools to build a model as complex as you need. You then need a separate package (such as 3ML <https://github.com/threeML/threeML>) to fit that model to the data.

Some of the features which distinguish astromodels from other similar packages are:

  • a model can contain an arbitrary number of sources at different positions in the sky

  • parameters can be linked through any function (not only identity)

  • parameters can vary with auxiliary variables such as time. For example, you can build a model where some parameters vary with time, and you can fit the parameters of the function which describe this variability. Similary you can build models where parameters vary with the phase of a pulsar, and so on.

  • models can be saved in and loaded from YAML file (a human-readable format)

  • physical units are fully supported in input, but they are handled so that they don’t slow down the actual computation of the models.

Astromodels has been designed with performance as priority, and is considerably faster than other python-based solutions for the same problem, such as astropy.modeling and the modeling part of sherpa.

Note

Note for XSPEC users:

Starting from version 2.5.0 there is currently support for XSPEC installed via Conda via the xspec conda package (see here).

astromodels 2.5.0 is compatible with XSPEC 12.15.0, while 2.5.1 enables support for XSPEC 12.15.1. XSPEC versions lower than 12.12.0 are no longer supported.

If you compiled XSPEC from source, please set the environment variable ASTRO_XSPEC_VERSION to the version of XSPEC you are using in the build process and make sure to have the HEADAS environment variable set.

Support for xspec-modelsonly conda package has been discontinued. Please use the conda package xspec instead.

In astromodels 2.5.1 the internal logic for the normalization parameter for XSPEC additive models has changed to be consistent with sherpa and support XSPEC 12.15.1. This means that XS model files in the user data folder (usually ~/.astromodels/data/) need to be regenerated. This should be automatically taken care of and transparent to the users, but in case of errors, please remove these files manually and try to import XSPEC models again to trigger the new generation.

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