| Re: x error bars in Curvefit / MPFIT [message #44478] |
Wed, 15 June 2005 18:56 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Sean Davis <seand@colorado.edu> writes:
> In my fit, x represents a "raw" value read from an instrument (it's actually
> calculated from several other "raw" values), and y represents the "true"
> value from the calibration using a different instrument. The goal is to
> come up with a fit that can be applied to my raw data that best fits the
> "truth".
Commonly, X is considered to be the *in*dependent variable. You don't
mention any independent variables, although there must be one or more
for your experiment to be a useful one.
> For fitting using MPFITFUN or similar programs, one typically provides error
> bars in the y value. But in my case, I have known errors in both x and y.
What you want is a package called ODRPACK. It's in FORTRAN, not IDL,
but it does the kinds of things you want, and it's very well
documented. I've thought about incorporating some of that logic into
MPFIT, but it won't be happening soon.
Happy fitting,
Craig
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@REMOVEcow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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