How do I use an XSPEC user model in Sherpa? ![[New]](../imgs/new.gif)
XSPEC supports user models, that is compiled code that can be used to add new models to XSPEC. Examples can be found on the "More models for XSPEC" page. It is possible to use these models in XSPEC, although it may require making changes to the model code!
The convert_xspec_user_model contributed script will attempt to build a compiled Python module that can then be used in Sherpa. It requires two arguments - the name for the Sherpa module and the model file (often called "lmodel.dat") that defines the model (e.g. the model name, it's type, and the parameter values) - and will create and compile the code. It is similar to the XSPEC initpackage call.
As an example, using the XSTAR warm absorber mode: warmabs model, after downloading and unpacking the warmabs247.tar.gz file into its own directory, we can see from the README that
- using the model requires setting the WARMABS_DATA environment variable,
- the XSPEC build uses the command initpackage xstarmod lmodel.dat (sometimes changes need to be made to the source code to include the location of data files or to change various settings).
Note that the screen output is not guaranteed to match the output here: what is important to see is that it reports that the module can be loaded and what models are available.
% setenv WARMABS_DATA `pwd` % convert_xspec_user_model xstarmod lmodel.dat convert_xspec_user_model: 10 October 2023 name: xstarmod modelfile: lmodel.dat clobber: False Found one Fortran file. Found no C files. Found no C++ files. Processing 5 models. Using language interface: Fortran - single precision Using XSPEC version: 12.13.1e Processing /download/warmabs Installing build dependencies ... done Getting requirements to build wheel ... done Preparing metadata (pyproject.toml) ... done Building wheels for collected packages: xstarmod Building wheel for xstarmod (pyproject.toml) ... done Created wheel for xstarmod: filename=xstarmod-1.0-cp311-cp311-linux_x86_64.whl size=675941 sha256=988cdb11e2c0b14640cfed185617d6d0fba960ad9c0ae27bfe34b7bd1aa2fba5 Stored in directory: /tmp/pip-ephem-wheel-cache-woe3__i0/wheels/b0/f8/6c/84859c31235f040243f2e81f3b4cf045ccec0a41723bd9a086 Successfully built xstarmod Installing collected packages: xstarmod Successfully installed xstarmod-1.0 Testing out importing the model ... Import succeeded ------------------------------------------------------------------ Finished. You should be able to now say import xstarmod.ui from Sherpa. The following 5 models are available: xsumhotemis xsumhotabs xsumphotemis xsumwarmabs xsummultabs
These models can now be used from any directory - i.e. you do not need to start from this directory - and can be loaded with
sherpa> import xstarmod.ui Adding additive XSPEC local model: xsumhotemis Adding multiplicative XSPEC local model: xsumhotabs Adding additive XSPEC local model: xsumphotemis Adding multiplicative XSPEC local model: xsumwarmabs Adding multiplicative XSPEC local model: xsummultabs sherpa> create_model_component("xsumwarmabs", "warm") <XSUMwarmabs model instance 'xsumwarmabs.warm'> sherpa> print(warm) xsumwarmabs.warm Param Type Value Min Max Units ----- ---- ----- --- --- ----- warm.column thawed 0 -3 2 cm^-2 warm.rlogxi thawed 0 -4 5 warm.Cabund frozen 1 0 1000 warm.Nabund frozen 1 0 1000 warm.Oabund frozen 1 0 1000 warm.Fabund frozen 1 0 1000 warm.Neabund frozen 1 0 1000 warm.Naabund frozen 1 0 1000 warm.Mgabund frozen 1 0 1000 warm.Alabund frozen 1 0 1000 warm.Siabund frozen 1 0 1000 warm.Pabund frozen 1 0 1000 warm.Sabund frozen 1 0 1000 warm.Clabund frozen 1 0 1000 warm.Arabund frozen 1 0 1000 warm.Kabund frozen 1 0 1000 warm.Caabund frozen 1 0 1000 warm.Scabund frozen 1 0 1000 warm.Tiabund frozen 1 0 1000 warm.Vabund frozen 1 0 1000 warm.Crabund frozen 1 0 1000 warm.Mnabund frozen 1 0 1000 warm.Feabund frozen 1 0 1000 warm.Coabund frozen 1 0 1000 warm.Niabund frozen 1 0 1000 warm.Cuabund frozen 1 0 1000 warm.Znabund frozen 1 0 1000 warm.write_outfile frozen 0 0 1 warm.outfile_idx frozen 0 0 10000 warm.vturb frozen 0 0 10000 km/s warm.Redshift frozen 0 0 10
The script comes with a number of options, including changing the prefix "xsum" to "xs" or having no prefix, and support for models that require the FORTRAN udmget routine.
![[NOTE]](../imgs/note.png)
Please contact the CXC Helpdesk if you find there are models which this script will not convert, or where the results do not appear to match XSPEC.