get_staterror

Context: data

Synopsis

Return the statistical errors on the counts of a data set

Syntax

get_staterror( [id, filter=False, bkg_id] )

The get_staterror() function returns the statistical errors on the counts of a source or background data set, by data id or bkg_id. The statistical errors returned are either those calculated by the current statistics or set by the user with set_staterror(). If a data filter has been applied to the data set in question, e.g. ignore() or notice(), the statistical error array for either the filtered or unfiltered data set may be returned by setting the 'filter' argument to 'True' or 'False'. If set to 'True', the statistical error array returned by get_staterror() will be filtered, i.e. the array will be shorter in length than the unfiltered array (not padded with zeros).

id - the id of the data set to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")
filter - apply an established data filter to the data set before returning results; default=False
bkg_id - the id of the background to use, e.g. if more than one background is associated with the data; default is the first background data set loaded

Example 1

sherpa> get_staterror()

When called with no arguments, the get_staterror() function returns the statistical error array of the unfiltered default data set.

sherpa> get_staterror()

array([  1.8660254 ,   1.8660254 ,   1.8660254 ,   1.8660254 ,
         1.8660254 ,   1.8660254 ,   1.8660254 ,   1.8660254 ,
. . . ., 
       2.32287566,   2.6583124 ,   2.6583124 ,   2.32287566,
         1.8660254 ,   2.93649167,   2.32287566,  18.25543393])

Example 2

sherpa> get_staterror(1, bkg_id=1)

To return the statistical error array of a background associated with a data set, the background ID must be specified along with the data set ID. Here, the statistical error array for the first background loaded for data set 1 is returned by get_staterror().

sherpa> get_staterror(1, 1)        

array([  1.8660254 ,   1.8660254 ,   1.8660254 ,   1.8660254 ,
         1.8660254 ,   1.8660254 ,   1.8660254 ,   1.8660254 ,
. . . ., 
       2.32287566,   2.6583124 ,   2.6583124 ,   2.32287566,
         1.8660254 ,   2.93649167,   2.32287566,  18.25543393])

Example 3

sherpa> get_staterror(1, filter=True)

If a data set ID is supplied to get_staterror(), the unfiltered statistical error array of the specified data set is returned, unless the 'filter' argument is set to 'True'.

sherpa> notice()
sherpa> get_staterror().size
           1024
sherpa> ignore(10,12)
sherpa> get_staterror(filter=True).size
           886

Bugs

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