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Re: Help Wanted: IDL Math Expert [message #9814 is a reply to message #9809]

Tue, 19 August 1997 00:00

Brad Gom
Messages: 49
Registered: August 1997

Member

Dr. Martin Ryba wrote:
>
> It sounds like the "raw data" has nonzero uncertainties in
> both the X and Y direction. Normal least-squares techniques assume a
> negligible error in the "independent variable" and are forming a

I'm assuming that the data has no error.

> If one can generate the T variable for
> each X,Y pair (which is kinda implied by your question), then I would
> concatenate the X and Y data together, each with its own copy of T, and
> use CURVEFIT to fit the combined data set with the concatenated set of
> free parameters.

I thought of doing this but I don't think I can generate the T variable
from the raw data.

To be more precise, my data is described by x(t)=sqrt(F/G) and
y(t)=sqrt(FG)
where F=a*((t^2)/b - t) and G=c*exp(sqrt(d/t))
I want the values of a,b,c, and d

I thought the following might work:
1. estimate parameters
2. calculate both x(t) and y(t) for range of t
3. compute difference between [x(t) vs y(t)] and the raw data
4. adjust parameters and return to 2. until fit

I could easily write this code except for step number 4. Would it be
possible to modify the curvefit
procedure to perform this step? I'm hoping I don't have to take a course
on nonlinear curve fitting to
solve this problem.

Thanx for the help

Brad Gom

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[Message index]

		Re: Help Wanted: IDL Math Expert By: David Ritscher on Wed, 20 August 1997 00:00
		Re: Help Wanted: IDL Math Expert By: John Votaw on Tue, 19 August 1997 00:00
		Re: Help Wanted: IDL Math Expert By: Jack Saba on Tue, 19 August 1997 00:00
		Re: Help Wanted: IDL Math Expert By: J.D. Smith on Tue, 19 August 1997 00:00
		Re: Help Wanted: IDL Math Expert By: Brad Gom on Tue, 19 August 1997 00:00
		Re: Help Wanted: IDL Math Expert By: Marty Ryba on Tue, 19 August 1997 00:00

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