get_error

Context: data

Synopsis

Return the total errors on the counts of a data set

Syntax

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

The get_error() function returns the total errors (statistical plus systematic in quadrature) on the counts in a source or background data set, by data id or bkg_id. If a data filter has been applied to the data set in question, e.g. ignore() or notice(), the counts 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 error array returned by get_error() 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_error()

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

sherpa> get_error()

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_error(1, filter=True)

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

sherpa> notice()
sherpa> get_error().size
           1024
sherpa> ignore(10,15)
sherpa> get_error(filter=True).size
           684

Example 3

sherpa> get_error(1, bkg_id=1)

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

sherpa> get_error(1, 1)         
array([ 1.8660254 ,  1.8660254 ,  1.8660254 ,  1.8660254 ,  1.8660254 ,
        1.8660254 ,  1.8660254 ,  1.8660254 ,  1.8660254 ,  1.8660254
        , . . . . . , 
        2.32287566,  1.8660254 ,  1.8660254 ,  1.8660254 ,  1.8660254 ,
        1.8660254 ,  2.32287566,  1.8660254 ,  9.76070773])

Bugs

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