sherpa.astro.ui.set_staterror(id, val=None, fractional=False, bkg_id=None)

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

These values over-ride the errors calculated by any statistic, such as chi2gehrels or chi2datavar.

  • 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.

  • val (array or scalar) – The systematic error.

  • fractional (bool, optional) – If False (the default value), then the val parameter is the absolute value, otherwise the val parameter represents the fractional error, so the absolute value is calculated as get_dep() * val (and val must be a scalar).

  • bkg_id (int or str, optional) – Set to identify which background component to set. The default value (None) means that this is for the source component of the data set.

See also


Load the statistical errors from a file.


Load the systematic errors from a file.


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


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


The function does not follow the normal Python standards for parameter use, since it is designed for easy interactive use. When called with a single un-named argument, it is taken to be the val parameter. If given two un-named arguments, then they are interpreted as the id and val parameters, respectively.


Set the statistical error for the default data set to the value in dys (a scalar or an array):

>>> set_staterror(dys)

Set the statistical error on the ‘core’ data set to be 5% of the data values:

>>> set_staterror('core', 0.05, fractional=True)