set_stat¶
-
sherpa.ui.set_stat(stat)¶ Set the statistical method.
Changes the method used to evaluate the fit statistic, that is the numerical measure that determines how closely the model represents the data.
- Parameters
stat (str) – The name of the statistic (case is not important). The list_stats function returns the list of supported values.
- Raises
sherpa.utils.err.ArgumentErr – If the
statargument is not recognized.
See also
calc_stat()Calculate the statistic value for a dataset.
get_stat_name()Return the current statistic method.
list_stats()List the supported fit statistics.
load_user_stat()Create a user-defined statistic.
Notes
The available statistics include:
- cash
A maximum likelihood function 1.
- chi2
Chi-squared statistic using the supplied error values.
- chi2constvar
Chi-squared with constant variance computed from the counts data.
- chi2datavar
Chi-squared with data variance.
- chi2gehrels
Chi-squared with gehrels method 2. This is the default method.
- chi2modvar
Chi-squared with model amplitude variance.
- chi2xspecvar
Chi-squared with data variance (XSPEC-style, variance = 1.0 if data less than or equal to 0.0).
- cstat
A maximum likelihood function (the XSPEC implementation of the Cash function) 3. This does not include support for including the background.
- wstat
A maximum likelihood function which includes the background data as part of the fit (i.e. for when it is not being explicitly modelled) (the XSPEC implementation of the Cash function) 3.
- leastsq
The least-squares statisic (the error is not used in this statistic).
References
- 1
Cash, W. “Parameter estimation in astronomy through application of the likelihood ratio”, ApJ, vol 228, p. 939-947 (1979). http://adsabs.harvard.edu/abs/1979ApJ…228..939C
- 2
Gehrels, N. “Confidence limits for small numbers of events in astrophysical data”, ApJ, vol 303, p. 336-346 (1986). http://adsabs.harvard.edu/abs/1986ApJ…303..336G
- 3(1,2)
https://heasarc.gsfc.nasa.gov/xanadu/xspec/manual/XSappendixStatistics.html
Examples
>>> set_stat('cash')