Re: Help: Weighted quadratic fitting under IDL?

[Martin Schultz <martin.schultz(at)dkrz.de>]

There is only one answer:  MPFIT

Grab it from http://cow.physics.wisc.edu/~craigm/idl/


Cheers,
Martin


"Brad K. Gibson" wrote:
> 
> This may be a highly trivial question, but it's one I'm having problems
> dealing with under IDL.  Perhaps I"m simply missing something obvious ..
> regardless, I'd be indebted if someone could help me out.  Heck, I'll even
> throw in a nice acknowledgement in my next paper, if someone could point me to
> a simple solution, or provide the requisite few lines of code!
> 
> Anyways ... here it is ... the equation of interest is of the form:
> 
>        Vmax - 5*log(v) = a[m15-1.1] + b[m15-1.1]^2 + c
> 
> I have a data file with Vmax, v, and m15 for a set of objects (about 40 of
> them), with uncertainties on each value.
> Having read those entries in, what I want to do is fit the above
> functional form, deriving a, b, and c, as well as their associated
> uncertainties (i.e. a +/- sig(a), b +/- sig(b), and c+/-sig(c)), and the final
> dispersion (and maybe reduced chi-squared) of the best fit quadratic.
> 
> Now .. I can see various routines which get me part-way there, but they either
> only provide a,b, and c without uncertainties, or only provide the
> uncertainties for a linear fit (e.g. fitexy).  Basically what I'd like is a
> quadratic version of fitexy (i.e., sigmas on all returned coefficients+
> dispersion of fit+reduced chi-square).
> 
> Obviously there is a nice way to do this without doing Monte Carlo
> simulations, but anyone who could save me a few
> hours of hacking code would become my instant hero(ine).  Anyone?
> 
> Cheers,
>   Brad
> 
> --
>   Brad K. Gibson                           INTERNET: bgibson@casa.colorado.edu
>   CASA, University of Colorado                PHONE:   +1-303-492-6058
>   Campus Box 389                                FAX:   +1-303-492-7178
>   Boulder, CO, USA  80309-0389              http://casa.colorado.edu/~bgibson/

-- 
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[[ Dr. Martin Schultz   Max-Planck-Institut fuer Meteorologie    [[
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