Known Issues and Limitations for Sherpa 4.1

The Sherpa 4.1 software release still includes some known bugs, and some functionality is subject to caveats. Also, there is some changed or missing functionality with respect to Sherpa 3.4. For complete details on this release, see the release notes and the About the Sherpa Release webpage.

If you think you have found a bug in Sherpa which is not shown here, please submit a ticket to the CXC Helpdesk describing the problem.

Caveats

IPython Packaged with CIAO OTS

CIAO includes IPython in the CIAO OTS directory which is used by Sherpa and ChIPS to provide command-line user interfaces. These programs create an IPython profile in the directory $HOME/.ipython-ciao.

If IPython users want any personal customizations to be available when running CIAO, they will have to copy them from $HOME/.ipython to $HOME/.ipython-ciao.

User Python modules must not have the same name as CIAO/Sherpa modules.

When loading a module in Python, Python first looks in the current working directory for this module, then in the directories listed in the PYTHONPATH environment variable. Therefore, if you have a script named 'sherpa.py' in your current working directory, for example, Sherpa will fail to load because the script ./sherpa.py is loaded, not the code in the module ${ASCDS_INSTALL}/lib/python2.5/site-packages/sherpa. Please ensure that the names of your Python scripts do not exactly match those of Python modules packaged with CIAO.

RMF energy grid resolution must not exceed that of ARF

Sherpa 4.1 does not currently support the case where the RMF has energy bins of higher resolution than the ARF (an ARF with higher resolution than the RMF energy bins is supported). Sherpa will print an error message when trying to fit data that have response grids unmatched in this way:"need to expand, not shrink effective area." The CIAO 'mkacisrmf' thread explains how to remake the ARF such that the grids match.