get_staterror¶

sherpa.astro.ui.get_staterror(id=None, filter=False, bkg_id=None)

Return the statistical error on the dependent axis of a data set.

The function returns the statistical errors on the values (dependenent axis) of a data set, or its background. These may have been set explicitly - either when the data set was created or with a call to set_staterror - or as defined by the chosen fit statistic (such as “chi2gehrels”).

Parameters
• id (int or str, optional) – The identifier for the data set to use. If not given then the default identifier is used, as returned by get_default_id.

• filter (bool, optional) – Should the filter attached to the data set be applied to the return value or not. The default is False.

• bkg_id (int or str, optional) – Set if the values returned should be from the given background component, instead of the source data set.

Returns

staterrors – The statistical error for each data point. This may be estimated from the data (e.g. with the chi2gehrels statistic) or have been set explicitly (set_staterror). For PHA data sets, the return array will match the grouping scheme applied to the data set. The size of this array depends on the filter argument.

Return type

array

Raises

sherpa.utils.err.IdentifierErr – If the data set does not exist.

get_error()

Return the errors on the dependent axis of a data set.

get_indep()

Return the independent axis of a data set.

get_syserror()

Return the systematic errors on the dependent axis of a data set.

list_data_ids()

List the identifiers for the loaded data sets.

set_staterror()

Set the statistical errors on the dependent axis of a data set.

Notes

The default behavior is to not apply any filter defined on the independent axes to the results, so that the return value is for all points (or bins) in the data set. Set the filter argument to True to apply this filter.

Examples

If not explicitly given, the statistical errors on a data set may be calculated from the data values (the independent axis), depending on the chosen statistic:

>>> load_arrays(1, [10, 15, 19], [4, 5, 9])
>>> set_stat('chi2datavar')
>>> get_staterror()
array([ 2.        ,  2.23606798,  3.        ])
>>> set_stat('chi2gehrels')
>>> get_staterror()
array([ 3.17944947,  3.39791576,  4.122499  ])


If the statistical errors are set - either when the data set is created or with a call to set_staterror - then these values will be used, no matter the statistic:

>>> load_arrays(1, [10, 15, 19], [4, 5, 9], [2, 3, 5])
>>> set_stat('chi2datavar')
>>> get_staterror()
array([2, 3, 5])
>>> set_stat('chi2gehrels')
>>> get_staterror()
array([2, 3, 5])