Chandra X-Ray Observatory
Skip to the navigation links
Last modified: December 2013

Jump to: Description · Examples · Bugs · See Also

AHELP for CIAO 4.9 Sherpa v1


Context: filtering


Apply an exclude filter to all 1D data sets


ignore( [lo,hi] )
ignore( expr )


Specifies an interval of 1D data to be excluded in all available data sets in a Sherpa session. To operate on specific data sets by ID, use the ignore_id command ("ahelp ignore_id").

  • lo: lower bound of the filter; default=None
  • hi: upper bound of the filter; default=None
  • expr: a filter expression to ignore an intersection of filters, e.g. "0.1:5, 6:7". Range filtering allows for an open-ended range of values, so that ":2" excludes data up to, or "2:" beginning at, the given value (2 here), respectively.

The units for the limits are determined by the "units" field of the data structure: channels, energy (keV), or wavelength (angstrom). The value can be obtained by using the get_analysis command ("ahelp get_analysis").

If the data is binned (or grouped) and the endpoint of the interval falls within a bin (group), the entire bin (group) is included in the filter. Note that the bin (group) with the last channel which has the energy included in the filter will be ignored by the filter.

Two-dimensional Data Filtering

To apply an exclude filter to 2D data, use the ignore2d command ("ahelp ignore2d") or the ignore2d_id command ("ahelp ignore2d_id").

Example 1

sherpa> ignore()

The ignore() function can be called with no arguments, in which case the filter will ignore all data points on the grid for all available data set IDs. Use before notice for cleaning the old filters.

Example 2

sherpa> ignore(1.0, 6.0)
sherpa> show_filter()
Data Set Filter: 1
0.0080-0.0803,6.0079-14.9431 Energy (keV)

Supplying an interval will apply a filter to all available data set IDs. show_filter() shows the effect of the energies left after the filter has been applied to the data.

Example 3

sherpa> group_counts(20)
sherpa> ignore(1.0,6.0)
sherpa> show_filter()
Data Set Filter: 1
6.3729-13.4101 Energy (keV)

For grouped data, the edge group containing the channels corresponding to the energies within the defined filter will be ignored, which may result in a broader ignored energy range. show_filter() shows the effect of grouping on the filter in this example.

Example 4

sherpa> ignore("0.1:5, 6:7")

Ignore the bins between 0.1 and 5 keV and between 6 and 7 keV.

Example 5

sherpa> ignore(7.,None)
sherpa> ignore(None, 0.5)

or the equivalent expression:

sherpa> ignore(":0.5,7.:")

An interval with the default lower-bound will filter all data points on the grid below the specified upper-bound. An interval with the default upper-bound will filter all data points on the grid above the specified lower-bound. Note that for grouped data, the filtered energy-limits could be different due to the boundaries of the group. If the channels in the groups correspond to the energies defined by the filter, these channels will be ignored. This impacts the edges of the resulting energies.


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

See Also

get_filter, ignore2d, ignore2d_id, ignore_bad, ignore_id, notice, notice2d, notice2d_id, notice_id, show_filter

Last modified: December 2013
Smithsonian Institute Smithsonian Institute

The Chandra X-Ray Center (CXC) is operated for NASA by the Smithsonian Astrophysical Observatory. 60 Garden Street, Cambridge, MA 02138 USA.   Email: Smithsonian Institution, Copyright © 1998-2017. All rights reserved.