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Re: Fitting an implicit function with IDL [message #71302 is a reply to message #71291]

Tue, 08 June 2010 16:47

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

On Jun 8, 6:54 am, Gianluca Li Causi <lica...@mporzio.astro.it> wrote:
> Hi all,
> I have to find the A, B and C parameters which best satisfy (in the
> chi-square sense) the following equation:
>
> A * g(x) + (W(x) + B) / (X(x) + C) = 0
>
> where g(x) is a known function of x and (W +/- sigmaW) and (Z +/-
> sigmaZ) are two sets of measured data together with their measurement
> errors.
>
> This is different from the usual form F(x, A,B,C) = Y where a function
> of x and parameters is to be fitted to a dataset (Y +/- sigma_Y).
> So, how to use the various IDL fitting routines to solve this
> problem??

I think what you really want to use is the FORTRAN library ODRPACK.

As Heinz Stege said, you can use curve fitting programs as equation
solvers. I actually did an IDL workshop presentation on this very
type of application. [*]

What I am not quite sure is how you include the data uncertainties in
the model.

Craig

[*] http://cow.physics.wisc.edu/~craigm/idl/fitting.html

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[Message index]

		Re: Fitting an implicit function with IDL By: Gianluca Li Causi on Wed, 09 June 2010 04:17
		Re: Fitting an implicit function with IDL By: Craig Markwardt on Tue, 08 June 2010 16:47
		Re: Fitting an implicit function with IDL By: Heinz Stege on Tue, 08 June 2010 15:29

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