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Last modified: 21 September 2006
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.

Frequently Asked Questions

The Frequently Asked Questions (FAQ) page is a place where users can find answers to the most common Sherpa questions. The CXC Helpdesk also has a searchable database, where users can look through all public Helpdesk questions.

I/O | Models & Parameters | Fitting | Plotting | Error Calculation | User Models

I/O

Recording Output

  1. Is there a way to capture all the screen output from Sherpa?

Case Sensitivity

  1. Why are some Sherpa commands case-sensitive, while others aren't?

S-Lang commands

  1. How can I control whether Sherpa or S-Lang interprets a command?


Models & Parameters

Linking Multiple Model Parameters

  1. When fitting two spectra simultaneously, is there a way to vary one model, but keep the ratio of normalizations between different models the same?

Parameter Ranges

  1. How do I change parameter minimum and maximum range limits?

Parameter Estimation

  1. How do I restore the default values of the parameters used to configure each Sherpa parameter-estimation method?


Fitting

Sherpa vs. XSPEC

  1. Why do my fit results from Sherpa and XSPEC differ by so much?
  2. How is error handling done in Sherpa as opposed to XSPEC?

Spectra

  1. Why doesn't Sherpa fit my PHA spectra?

Model Parameters

  1. Why didn't the value of my thawed parameters change in the fit?
    How is this different than just freezing that parameter?


Plotting

General

  1. Why doesn't Sherpa plot in energy scale, even if I enter "PLOTX 2 ENERGY"?
  2. How do I make a log-log plot?
    How do I return to linear axes?


Error Calculation

General

  1. How can I determine the uncertainty in a flux measurement?

Projection

  1. What does this warning mean?
    WARNING: upper projection bound not found for (parameter name)


User Models

General

  1. My user model worked in CIAO 2.3. Why won't it work in CIAO 3?
Hardcopy (PDF): A4 | Letter
Last modified: 21 September 2006

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