calc_stat

calc_stat( [ id, [otherids]] );

Description

The function calc_stat returns the value of the fit statistic for the data set ID(s) specified; the data set ID(s) supplied to calc_stat must be ready for fitting, i.e. it has been assigned a model to be fit. The calc_stat function can be called with no arguments, in which case the fit statistic for the default data set ready for fitting will be returned. If multiple data set IDs are given, then the simultaneous fit statistic is calculated for those data sets. The fit statistic value returned by calc_stat represents the initial fit statistic, which matches the "istatval" value returned by get_fit_results.

• id, otherids - the id(s) of the dataset(s) to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id"); otherids=NULL

Below are the fit statistics available in Sherpa:

chi2constvar	\chi^2 with constant variance computed from the counts data.
chi2modvar	\chi^2 with model amplitude variance.
chi2gehrels	\chi^2 with gehrels method (default).
chi2datavar	\chi^2 with data variance.
chi2xspecvar	\chi^2 with data variance (XSPEC-style, variance = 1.0 if data less than or equal to 0.0)
cstat	CStat - A maximum likelihood function (XSPEC implementation of Cash).
cash	Cash - A maximum likelihood function.

sherpa> calc_stat();

sherpa> calc_stat(1);
sherpa> calc_stat("src");

sherpa> calc_stat(1,2);
sherpa> calc_stat("src", "bkg");