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Last modified: December 2010

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AHELP for CIAO 4.3 Sherpa v1


Context: utilities


Calculate the sum of unconvolved model amplitudes


calc_source_sum( [lo,hi,id,bkg_id] )


The calc_source_sum function calculates the sum of unconvolved source or background model amplitudes for all or a portion of a source or background data set by data ID or background ID. A subset of the model can be specified by entering the low and high ends of the desired data interval in units of keV for energy data or Angstroms for wavelength data. To sum the counts of convolved source or background models, the function calc_model_sum can be used by data ID or background ID.

  • lo - low limit; default=None
  • hi - high limit; default=None
  • id - data ID; if not given, uses the default sherpa id (id=1 by default, see "ahelp get_default_id")
  • bkg_id - background data ID

The command ignores any range filters that have been applied to the dataset. If calc_source_sum is called with no arguments, the unconvolved model amplitudes will be summed over the entire data range of the default data set.

The amplitudes of an unconvolved background model can be summed by supplying the corresponding Sherpa-assigned background ID as the argument (e.g. "1" or "2" for the first or second background data set automatically located by Sherpa in the corresponding source data set).

For 1-D data, if:

o) one energy (or wavelength) is given (as opposed to a [lo, hi] interval), then the model amplitude at that energy (or wavelength) is returned in units of counts/cm^2/sec/keV (or counts/cm^2/sec/A).

o) an energy or wavelength range is given with the 'lo' and 'hi' arguments, then the total integrated model amplitudes over the given range is returned in units of counts/cm^2/sec.

o) no value or range is specified, then the total integrated model amplitude over the full range of the dataset is returned in units of counts/cm^2/sec.

For 1-D data, if an instrument model is not used, the units are assumed to be counts, or counts per bin-width. See the Note on Units below.

For 2-D data the total integrated model amplitudes is carried out over the entire input image.

Note on Units: In its current incarnation, Sherpa has no explicit knowledge of data or model units. The units displayed with computed fluxes are defaults, generally correct for standard analyses of 1-D PHA energy/wavelength spectra (XSPEC-like analyses). They may be incorrect for non-standard analyses, or for analyses of 2-D spatial images with exposure maps, etc. The correct units can be determined by working backwards from the data, taking into account the exposure time, the units of the instrument model, the bin units, etc.

Example 1

sherpa> calc_source_sum()

When supplied with no arguments, calc_source_sum will sum the unconvolved model amplitudes over the entire data range of the default data set.

Example 2

sherpa> calc_source_sum(bkg_id=1)

When supplied with a background ID, the amplitudes of the unconvolved background model associated with the specified background data set will be summed over the entire data range. In this example, the first background data set automatically located by Sherpa is used.

Example 3

sherpa> calc_source_sum(lo=0.1, hi=7.0, "bkg")

The unconvolved background model amplitudes between 0.1 and 7.0 keV are summed for the background data set with user-assigned ID "bkg". (Note that a user-defined string ID cannot be supplied to the "bkg_id" argument.)

Example 4

sherpa> calc_source_sum(1., 15., 1, 2)

The unconvolved background model amplitudes between 1 and 15 angstroms are summed for the second background data set automatically loaded by Sherpa with source data set 1.


See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

See Also

list_model_ids, show_bkg_model, show_bkg_source
add_model, add_user_pars, clean, create_model_component, delete_bkg_model, delete_model, delete_model_component, get_model, get_model_autoassign_func, 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_source, get_source_component_image, get_source_component_plot, image_model, image_model_component, image_source, image_source_component, integrate, link, load_table_model, load_user_model, reset, save_model, save_source, set_bkg_model, set_full_model, set_model_autoassign_func, set_pileup_model, set_source, set_xsabund, set_xscosmo, set_xsxsect, set_xsxset
plot_model, plot_model_component, plot_source, plot_source_component
delete_psf, load_conv
save_delchi, save_resid
calc_chisqr, calc_energy_flux, calc_model_sum, calc_photon_flux, calc_stat, eqwidth, gamma, igam, igamc, incbet, lgam
contour_model, contour_ratio, contour_resid, get_ratio, get_resid

Last modified: December 2010
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