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Re: Help with constrained fit in IDL

George A. Lengel wrote:
Hi all,

I have written some IDL code to fit our data with a power law and it
works fine. Now I am trying to constrain the fit to use a specific value
of an exponent and only vary the factor in front of the expression. I
cannot get this to work properly, and I think it should be simpler
than I am making it out to be. I figure this is due to my relative
inexperience with the FUNCT keyword and how the data fitting is done
in IDL. Can anyone give me a hint for proceeding with performing a fit
to data that constrains one of the factors to a specific value?

Thanks for any pointers that are given.

George Lengel                        mailto:lengel@lps.umd.edu
Laboratory for Physical Sciences  OR mailto:lengel@glue.umd.edu
University of Maryland
***I certainly do not speak for LPS or UMd in any capacity******

Hi George,

we have modified the Curvefit from IDL, so that you can fix paramters to a specified value.
The result is, that you need only one Fitfunction-procedure for your fit
instead of defing a new procedure for every set of free parameters.
Furthermore we corrected the curvefit-procedure in some points.
E.g. the errors for the parameters are now the correct ones, also you have a correlation matrix as output.
Send an email to me, if you want to get my curvefit-routine.


Heiko Hünnefeld

Notkestr. 85 
22603 Hamburg
Tel.: 040 / 8998-2698
Fax.: 040 / 8998-2787
e-mail: hhuenne@desy.de