|AHELP for CIAO 4.9 Sherpa v1||
Parses the goodness-of-fit statistic information returned by calc_stat_info()
The get_stat_info() function is available for parsing the output of the calc_stat_info() function, which returns the goodness-of-fit statistics associated with a data set and its assigned model. The advantage it offers over the get_fit_results() function is that it returns statistics on individual data sets included in a simultaneous fit, plus the statistics of the simultaneous fit, whereas get_fit_results() would only return the statistics of the simultaneous fit. The get_stat_info() function is useful for accessing and manipulating individual components of the calc_stat_info() structure, e.g. within a script, whereas calc_stat_info() is recommended for printing fit statistic information to the screen, at the Sherpa command line.
The get_stat_info() function returns the following information about how well the specified models fit the data:
- name - name of data set
- ids - data set ID number
- bkg_ids - associated background data set ID number
- statname - the chosen fit statistic
- statval - fit statistic value
- numpoints - number of bins in the fit
- dof - the number of degrees of freedom in the fit, i.e. the number of bins minus the number of free parameters
- qval - [only reported with chi-square, 'cstat', and 'wstat' statistics] a measure of the (Q-value) probability that one would observe the reduced statistic value, or a larger value, if the assumed model is true and the best-fit model parameters are the true parameter values
- rstat - [only reported with chi-square, 'cstat', and 'wstat' statistics] fit statistic value divided by the number of degrees of freedom
This function accepts no arguments; it returns the fit statistics for all data sets which have been assigned models, including background data sets associated with source data sets. This means that if a fit has not yet been performed in the Sherpa session, calc_stat_info() will return not-very-meaningful statistics for data sets which have been assigned models but which have not yet been fit. Also, if a fit has been performed for only some of the data sets with assigned models, those data sets which were not explicitly fit will be included in the simultaneous fit results returned by calc_stat_info() (see an example of this behavior below in the examples section).
sherpa> set_source(xsphabs.abs1 * powlaw1d.p1) sherpa> set_bkg_model("p1") sherpa> fit() sherpa> statinfo = get_stat_info() sherpa> print(statinfo) sherpa> print(statinfo) sherpa> print(statinfo)
Return the statistics resulting from a simultaneous fit of the source and background spectra assigned to default data set 1. Print the goodness-of-fit statistics for each individual data set included in the fit, plus the simultaneous fit.
sherpa> print(get_stat_info()) name = Dataset 1 ids = (1,) bkg_ids = None statname = chi2gehrels statval = 5506.18997409 numpoints = 1024 dof = 1021 qval = 0.0 rstat = 5.39293827041 sherpa> print(get_stat_info()) name = Background 1 for Dataset 1 ids = (1,) bkg_ids = (1,) statname = chi2gehrels statval = 15975.5866119 numpoints = 1024 dof = 1022 qval = 0.0 rstat = 15.6316894441 sherpa-23> print(get_stat_info()) name = Dataset  ids =  bkg_ids = None statname = chi2gehrels statval = 21481.776586 numpoints = 2048 dof = 2045 qval = 0.0 rstat = 10.5045362279
sherpa> load_pha("source.pi") sherpa> load_arf("arf1.fits") sherpa> load_rmf("rmf1.fits") sherpa> set_source(xsphabs.abs1 * xspowerlaw.p1) sherpa> subtract() sherpa> fit() sherpa> calc_stat_info() sherpa> f = get_stat_info() sherpa> print(f.rstat)
The calc_stat_info() function is used to return the goodness-of-fit statistics resulting from the fit of an absorbed power law model to background-subtracted data set 1. The get_stat_info() function is used to parse this information and store the fit statistic information to variable "f"; "f" is then used in turn to access the reduced statistic value.
sherpa> calc_stat_info() Dataset = 1 Statistic = chi2gehrels Fit statistic value = 703.792 Data points = 1024 Degrees of freedom = 1021 Probability [Q-value] = 1 Reduced statistic = 0.689316 sherpa> f = get_stat_info() sherpa> print(f) name = Dataset  ids =  bkg_ids = None statname = chi2gehrels statval = 703.791857589 numpoints = 1024 dof = 1021 qval = 1.0 rstat = 0.689316217031 sherpa> print(f.rstat) 0.689316217031
The get_stat_info() routine fails with the message "StatErr: No background data has been supplied. Use cstat" when used with the wstat statistic.
See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.
- get_conf, get_covar, get_int_proj, get_int_unc, get_proj, get_reg_proj, get_reg_unc
- get_areascal, get_arf, get_arf_plot, get_axes, get_backscal, get_bkg, get_bkg_plot, get_bkg_scale, get_coord, get_counts, get_data, get_data_plot, get_dep, get_dims, get_error, get_exposure, get_grouping, get_indep, get_quality, get_rmf, get_specresp, get_staterror, get_syserror
- calc_stat_info, get_fit
- get_default_id, list_stats
- get_draws, get_iter_method_name, get_iter_method_opt, get_method
- get_model, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_order_plot, get_par, get_pileup_model, get_response, get_source, get_source_component_image, get_source_component_plot, image_source
- get_kernel, get_psf
- get_chisqr_plot, get_delchi_plot, get_prior, get_sampler, get_stat
- get_analysis, get_rate
- get_ratio, get_resid, image_getregion