Synopsis
Return the background scaling factor for a background data set.
Syntax
get_bkg_scale(id=None, bkg_id=1, units='counts', group=True, filter=False) id - int or str, optional bkg_id - int or str, optional units - {'counts', 'rate'}, optional group - bool, optional filter - bool, optional
Description
Return the factor applied to the background component to scale it to match it to the source, either when subtracting the background (units='counts'), or fitting it simultaneously (units='rate').
Examples
Example 1
Return the background-scaling factor for the default dataset (this assumes there's only one background component).
>>> get_bkg_scale() 0.034514770047217924
Example 2
Return the factor for dataset "pi":
>>> get_bkg_scale('pi') 0.034514770047217924
Example 3
Calculate the factors for the first two background components of the default dataset, valid for combining the source and background models to fit the source aperture:
>>> scale1 = get_bkg_scale(units='rate') >>> scale2 = get_bkg_scale(units='rate', bkg_id=2)
PARAMETERS
The parameters for this function are:
Parameter | Definition |
---|---|
id | The identifier for the data set to use. If not given then the default identifier is used, as returned by `get_default_id` . |
bkg_id | Set to identify which background component to use. The default value is 1. |
units | The correction is applied to a model defined as counts, the default, or a rate. The latter should be used when calculating the correction factor for adding the background data to the source aperture. |
group | Should the values be grouped to match the data? |
filter | Should the values be filtered to match the data? |
Return value
The return value from this function is:
ratio -- The scaling factor. The result can vary per channel, in which case an array is returned.
Notes
The scale factor when units='counts' is:
exp_src * bscale_src * areascal_src / (exp_bgnd * bscale_bgnd * areascal_ngnd) / nbkg
where exp_x , bscale_x . and areascal_x are the exposure, BACKSCAL, and AREASCAL values for the source ( x=src ) and background ( x=bgnd ) regions, respectively, and nbkg is the number of background datasets associated with the source aperture. When units='rate', the exposure and areascal corrections are not included.
Changes in CIAO
Changed in CIAO 4.13
The bkg_id, counts, group, and filter parameters have been added and the routine no-longer calculates the average scaling for all the background components but just for the given component.
Bugs
See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.
See Also
- confidence
- get_conf, get_conf_results, get_covar, get_covar_opt, get_covar_results, get_covariance_results, get_int_proj, get_int_unc, get_proj, get_proj_opt, get_proj_results, get_projection_results, get_reg_proj, get_reg_unc
- contrib
- get_chart_spectrum, get_marx_spectrum
- data
- get_areascal, get_arf, get_arf_plot, get_axes, get_backscal, get_bkg, get_bkg_arf, get_bkg_chisqr_plot, get_bkg_delchi_plot, get_bkg_fit_plot, get_bkg_model, get_bkg_model_plot, get_bkg_plot, get_bkg_ratio_plot, get_bkg_resid_plot, get_bkg_rmf, get_bkg_source, get_bkg_source_plot, get_coord, get_counts, get_data, get_data_contour, get_data_contour_prefs, get_data_image, get_data_plot, get_data_plot_prefs, get_dep, get_dims, get_error, get_exposure, get_grouping, get_indep, get_quality, get_rmf, get_specresp, get_staterror, get_syserror
- filtering
- get_filter
- fitting
- calc_stat_info, get_stat_info
- info
- get_default_id, list_stats
- methods
- get_draws, get_iter_method_name, get_iter_method_opt, get_method, get_method_name, get_method_opt
- modeling
- get_model, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_num_par_frozen, get_num_par_thawed, get_order_plot, get_par, get_pileup_model, get_response, get_source, get_source_component_image, get_source_component_plot, get_source_contour, get_source_image, get_source_plot, image_source
- plotting
- get_split_plot
- psfs
- get_psf, get_psf_contour, get_psf_image, get_psf_plot
- statistics
- get_chisqr_plot, get_delchi_plot, get_prior, get_sampler, get_stat, get_stat_name
- utilities
- get_analysis, get_rate
- visualization
- image_getregion