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Last modified: 21 September 2006

URL: http://cxc.harvard.edu/sherpa3.4/bugs/fit_statistic.html
Hardcopy (PDF): A4 | Letter

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11 Nov 2008

These are the webpages relative to Sherpa in the CIAO 3.4 release (18 December 2006). They are no longer actively updated, however the CXC will continue limited support of CIAO 3.4 for the near future.

15 Dec 2008

The newest version of the Chandra Interactive Analysis of Observations software, is CIAO 4.1, released on 15 December 2008. Read the release notes for detailed information. This release requires that CALDB 4.1.0 be installed for the software to work correctly.

Fitting Bugs: statistic

Return to: Bug List Index

Bugs

  1. When using "chi dvar" and different backscales for source and background (i.e. the most likely case for imaging spectra), some of the points can have a very low data variance and will negatively affect the fit.

  2. The Bayes statistic does not work with the Levenberg-Marquardt fitting algorithm, which is the default fitting algorithm in Sherpa.

Bugs

  1. When using "chi dvar" and different backscales for source and background (i.e. the most likely case for imaging spectra), some of the points can have a very low data variance and will negatively affect the fit.

  2. The Bayes statistic does not work with the Levenberg-Marquardt fitting algorithm, which is the default fitting algorithm in Sherpa.

    In order to use this statistic, the method command much be used to change to a different optimization method; the most commonly used optimizations are simplex or Powell .

Hardcopy (PDF): A4 | Letter
Last modified: 21 September 2006

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