Defines an expression or file to be used to specify the
systematic errors for background data.
sherpa> BSYSERRORS [<dataset range> | ALLSETS] [ID] = <errorExpr>
<dataset range> = # (or more generally #:#,#:#, etc.) such that #
specifies a dataset number and #:# represents an inclusive range of
datasets; one may specify multiple inclusive ranges by separating them
with commas. The default dataset is dataset 1. The ID modifier is used
if and only if the Sherpa state object variable multiback is set to 1,
i.e., if more than one background dataset is to be associated with a
single source dataset. The ID modifier may be any unreserved string
(e.g., A, foo, etc.), i.e., a string that is not a parsable command.
The error expression, <errorExpr>, may be composed of one or
more (algebraically-combined) of the following elements:
| BACK | An input background dataset |
| numericals | Numerical values |
| operators | + - * / ( ) |
A few things to note:
-
Background systematic error expressions cannot be defined without
first reading in a background dataset.
-
The input systematic error for a given bin is first multiplied by the
datum in that bin; the resulting product is added in quadrature with
the statistical error to yield the overall error for that bin.
-
The background systematic errors can be
specified in an input file; see READ
BSYSERRORS for more information.
-
If the background systematic errors are not defined using the
BSYSERRORS command or input using READ BSYSERRORS,
they are assumed to be zero.
For additional information, see the related command BERRORS.
The background systematic errors are accessible to the
Sherpa/S-Lang module
user via the functions
get_bsyserrors and
set_bsyserrors.
Define an expression to be used for the background systematic errors. In
each bin, they will be computed as 0.1 times the background datum.
sherpa> DATA data.dat
sherpa> BACK back.dat
sherpa> BSYSERRORS = 0.1
- chandra
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