INVERTFIT or EVALFIT for CCD

Robert Janusz wrote on Sep 06, 2007

What are the reasons to use INVERTFIT method rather than EVALFIT for CCD photometry as IRAF HELP on MKCONFIG suggests?

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Francisco Valdes wrote on Sep 06, 2007

The result of inverting a fit is what is usually needed to evaluate the functions for observed stars.

Frank Valdes

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Robert Janusz wrote on Sep 06, 2007

OK. The form of the equations for the INVERTFIT really needs to invert the transformation as "a system". Preparing the same problem we can use the EVALFIT without any invert. But in general we get different results (not only for fit parameters, as it should usually be) but for solution (values, residuals, etc.). Is there any physical reason for choosing the method? For the photoelectic data the help (mkconfig) prefers the EVALFIT form but for CCD data - INVERTFIT form. Why is so?

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Last post on Sep 06, 2007