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Re: Help: multiple linear regression fit [message #36195 is a reply to message #36185]

Tue, 12 August 2003 08:55

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

fishdick91@hotmail.com (fishdick91@hotmail.com) writes:

> Hi everyone,
>
> I've set up a model: y = a1*x1 + a2*x2 + a3*x3 to fit my experiment
> data,
> and am using 'regress' function to perform this fit.
> However, the 'regress' function always return a big const which I
> don't need.
> So question 1:
> how can I fix the const when fitting?

And what of the MPFIT family of functions? Using the driver
MPFITEXPR, you can set up an expression that almost exactly matches
your case:

EXPR = 'P(0)*X(*,0) + P(1)*X(*,1) + P(2)*X(*,2)'

(of course you need the core routine MPFIT too). You would need to
set up X as an Nx3 array, and Y as an N-vector.

Some people seem to resist using a non-linear regression tool for a
linear problem on the basis of, "it's *ONLY* linear regression!"
Originally I might explain that the heart of any non-linear regression
package is a linear solver, so it's really all the same. Recently I
just shrug and say, "their loss."

Happy fitting,
Craig

http://cow.physics.wisc.edu/~craigm/idl/idl.html (under fitting)

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		Re: Help: multiple linear regression fit By: fishdick91 on Tue, 12 August 2003 19:54
		Re: Help: multiple linear regression fit By: Craig Markwardt on Tue, 12 August 2003 08:55

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