fit_bkg

sherpa.astro.ui.fit_bkg(id: IdType | None = None, *otherids: IdType, **kwargs) → None

Fit a model to one or more background PHA data sets.

Fit only the background components of PHA data sets. This can be used to find the best-fit background parameters, which can then be frozen before fitting the data, or to ensure that these parameters are well defined before performing a simultaneous source and background fit.

Changed in version 4.17.0: The outfile parameter can now be sent a Path object or a file handle instead of a string.

Parameters:

  • id (int or str, optional) – The data set that provides the background data. If not given then all data sets with an associated background model are fit simultaneously.

  • *otherids (sequence of int or str, optional) – Other data sets to use in the calculation.

  • outfile (str, Path, IO object, or None, optional) – If set, then the fit results will be written to a file with this name. The file contains the per-iteration fit results.

  • clobber (bool, optional) – This flag controls whether an existing file can be overwritten (True) or if it raises an exception (False, the default setting). This is only used if outfile is set to a string or Path object.

Raises:

sherpa.utils.err.FitErr – If filename already exists and clobber is False.

See also

calc_bkg_stat, conf, contour_fit, covar, fit, freeze, get_fit_results, plot_fit, image_fit, set_stat, set_method, set_method_opt, set_bkg_full_model, set_bkg_model, set_full_model, set_iter_method, set_model, show_bkg_source, show_bkg_model, show_fit, thaw

Notes

This is only for PHA data sets where the background is being modelled, rather than subtracted from the data.

If outfile is sent a file handle then it is not closed by this routine.

Examples

Simultaneously fit all background data sets with models and then store the results in the variable fres:

>>> fit_bkg()
>>> fres = get_fit_results()

Fit the background for data sets 1 and 2, then do a simultaneous fit to the source and background data sets:

>>> fit_bkg(1, 2)
>>> fit(1, 2)

Store the per-iteration values in a StringIO object and extract the data into the variable txt (this avoids the need to create a file):

>>> from io import StringIO
>>> out = StringIO()
>>> fit_bkg(outfile=out)
>>> txt = out.getvalue()