Curve Fitting Problem

[A. Kalten]

On Thu, 26 Jun 2008 16:47:57 -0700
Scott Carter <scott at nklab.com> wrote:

> AK, in your specific example (which I assume contains a typo and should 
> really be (k^2/4)x^2, since as written it's linear)
> I don't see why you aren't just solving the linear regression for y = 
> (k/2)x + p
> 
> please explain what I'm missing
> 

Yes, that was a typo and should be (k^2/4)x^2.

When dealing with data that has error terms any transformation
of the data to get a linear relation is generally not a good idea.

But even transforming the data to get the linear model still
leaves p, which is a known quantity.  Functions such as
polyfit will expect both parameters to be unknown and
unconstrained.

I am looking for some off-the-shelf function that will allow
me to specify parts of the model and that will just determine
the unknown parameters.  There do not seem to be any off-the-shelf 
packages that will do this and probably the only recourse is
to do some custom programming.

AK