Sherpa Release Notes

CIAO 3.2 contains significant improvements to several Sherpa models. Updates have been made to error estimation, and the XSpec model library has been updated to v11.3.1. Sherpa can now be used with the S-Lang "require()" function; this change is in conjunction with the S-Lang module changes for provide and require.

The CIAO release notes contain a complete listing of changes made in this release. Release notes for previous versions of CIAO and Sherpa are available from the CIAO Version History.

Convolution with PSF Models

• Improvements to the file-based PSF models (fpsf1d, fpsf2d) and the point-source models (ptsrc1d, ptsrc2d) have been made.

• The ptsrc1d and ptsrc2d have been updated to accommodate both FITS and ASCII files.

• A bug in file-based PSF convolution (fpsf models) has been corrected.

Fitting Methods

The Levenberg-Marquardt fitting method has improved handling of problem datasets.

Error Estimation

• Improvements have been made to the projection method to handle the case of overflow and underflow errors:

  • the projection method now catches overflows and underflows, and calculates the errors for the remaining parameters rather than immediately exiting, and
  • the allowable range on many model parameters has been restricted to reduce the chances of overflow occurring.

• The error-estimation commands can now be run without first performing a fit. This allows users to load in a previous fitting session (saved with the "SAVE" command) and continue their analysis. This only holds for the Sherpa commands (e.g. PROJECTION, INTERVAL-UNCERTAINTY) and not the S-Lang versions (e.g. run_proj(), run_intunc()).

S-Lang Integration

• In a number of cases, cleaned up extraneous output from S-Lang functions. These include functions such as get_fit(), run_proj(), and sherpa_eval().

• Sherpa can now be used with the S-Lang "require()" function; this change is in conjunction with the S-Lang module changes for provide and require.

Miscellaneous Changes

• In the jdpileup model, some default parameter values and limits have been changed:

  • value of alpha changed from 0.95 to 0.5
  • f is now thawed
  • the upper limit for the n parameter is 100 (was 2048)
  • the lower limit for the g0, ftime, and fracexp parameters is 1e-120 (was 0)
  • value of fracexp changed from 1 to 0.987

• The CIAO 3.2 version of Sherpa links in the XSpec v11.3.1 model library, and includes interfaces to the new models in this library. The XSpec model function help file lists the models which are not available in CIAO 3.2.

• The CIAO 3.2 version of Sherpa makes use of version 0.4.0 of the S-Lang XPA module, in its CIAO 3 compatibility mode. This means that the ds9 package can not be used with Sherpa.

• Sherpa no longer overrides the ChIPS redraw setting. This means that ChIPS commands will be executed immediately, so users no longer need to issue the REDRAW command.

Bug Fixes

• The Sherpa bug pages list all currently known bugs, as well as those fixed in CIAO 3.2.

• get_fit always returned goodness-of-fit information for all datasets

• sherpa_eval() does not return -1 on a failed use command

• due to a round-off/casting problem, creating an ARF in double precision causes the source model to contain 0's when it shouldn't

• if a parameter value is at the maximum boundary, running projection on it may result in a core dump (Linux only)