Last modified: December 2023

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AHELP for CIAO 4.16 Sherpa


Context: fitting


Fit a model to one or more data sets.


fit(id=None, *otherids, **kwargs)

Alias: simulfit

id - int or str, optional
*otherids - sequence of int or str, optional
outfile - str, optional
clobber - bool, optional


Use forward fitting to find the best-fit model to one or more data sets, given the chosen statistic and optimization method. The fit proceeds until the results converge or the number of iterations exceeds the maximum value (these values can be changed with `set_method_opt` ). An iterative scheme can be added using `set_iter_method` to try and improve the fit. The final fit results are displayed to the screen and can be retrieved with `get_fit_results` .


Example 1

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

>>> fit()
>>> fres = get_fit_results()

Example 2

Fit just the data set 'img':

>>> fit('img')

Example 3

Simultaneously fit data sets 1, 2, and 3:

>>> fit(1, 2, 3)

Example 4

Fit data set 'jet' and write the fit results to the text file '', over-writing it if it already exists:

>>> fit('jet', outfile='', clobber=True)


The parameters for this function are:

Parameter Definition
id The data set that provides the data. If not given then all data sets with an associated model are fit simultaneously.
*otherids Other data sets to use in the calculation.
outfile If set, then the fit results will be written to a file with this name. The file contains the per-iteration fit results.
clobber This flag controls whether an existing file can be overwritten ( True ) or if it raises an exception ( False , the default setting).


For PHA data sets with background components, the function will fit any background components for which a background model has been created (rather than being subtracted). The `fit_bkg` function can be used to fit models to just the background data.


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

fit_bkg, get_fit_results, simulfit
get_iter_method_name, get_iter_method_opt, list_iter_methods, set_iter_method, set_iter_method_opt
freeze, set_bkg_full_model, set_bkg_model, set_full_model, set_model, thaw
plot_fit, plot_fit_delchi, plot_fit_resid
get_stat, get_stat_name
calc_chisqr, calc_stat
contour_resid, image_fit