Calculate the Chi Squared statistic contribution per bin
calc_chisqr( [ id, [otherids]] )
When fitting data with Chi Squared statistics, the calc_chisqr
function returns an array of Chi
Squared statistic contributions for each bin of the specified
data set ID(s). The data set ID(s) supplied
to calc_chisqr must be ready for fitting, i.e. it has been
assigned a model to be fit. The calc_chisqr function can be
called with no arguments, in which
case the Chi Squared statistic array for the first
data set ready for fitting
will be returned. If multiple data set IDs are given, then the
simultaneous Chi Squared fit statistics are
calculated for those data sets.
-
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=None
Below are the Chi Squared fit statistics available in Sherpa:
| 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) |
When called with no arguments, calc_chisqr() returns the
Chi Squared
statistic array for the default data set, if it has been assigned a
model to be fit.
sherpa> calc_chisqr(1)
sherpa> calc_chisqr("src")
Supplying a specific data set ID to calc_chisqr - such as
"1" or "src" - will return the Chi Squared
statistic array for only that data set.
sherpa> calc_chisqr(1,2)
sherpa> calc_chisqr("src", "bkg")
When supplied with multiple data set IDs, calc_chisqr
returns the Chi Squared statistic array produced by the
simultaneous fit on those data sets.
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