Institut für Astronomie und Astrophysik
Abteilung AstronomieSand 1, D-72076 Tübingen, Germany
reconstruct error column by fitting model
quiet - Do not show fit processing. selected - Apply fit to selected data points only.
All options may be set with the "set" command. The command prefix is "fiterror".
If the data set does not contain a error column the fit process assumes an error of 1 which leads to improper fit statistics. With this command it is possible to reconstruct an error using following assumptions: 1.) The error is basically the same for all data points. 2.) The model to fit is a good fit so the resulting reduced Chi^2 is 1. Of course these assumptions are not always justified, so this command should be used with care. This also means that for following fits the resulting reduced Chi^2 value is 1 and could not be used to establish a goodness of the fit. But the command may help for deriving a formal error by first selecting ranges of data points with well-known model features, reconstructing the error column and then apply this full data set to other regions where a closer model must be applied. If more than one data set is given all data sets which are involved in the fitting process are taken into account. Excluded are: - Groups without a defined model - Groups with a model but no valid data points. If a group contains defined but not selected data points and the option /selected was chosen this group is also ignored. Subgroups with unselected data points when the group is valid and the select option is used are noticed.
Use with care! Former error columns are modifierd; and the new error column of data may contain misleading values.
Adds error column to data set. Changes parameter values/errors in environment according fit result.
> model, lin ; apply simple model for first part > ignore, 100-* ; of data, which is flat > fiterror ; create error column > notice, * ; for all data: > model, lin+gauss; apply complex model > fit ; for a fit. -> fit exhibits a goodness of fit for the complex model
$Id: cafe_fiterror.pro,v 1.12 2004/05/27 07:33:38 goehler Exp $
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