Re: [Gnuplot-info] 3-d-fitting

[Spinora <N.M...@gm...>]

Thomas Sefzick wrote:
> 
> the first question you have to answer is:
> which function would describe your data best?
> 
> then use this function and set the parameters by hand, so that the
> function is already in the region where the datapoints are, and then start
> the fit.
> 
> if you start a fit with parameters set to values which cause the function
> to be far off the datapoints, then this fit will not work. due to the
> inadequate stepsize chosen automatically it may find some minimum but not
> the real one (for comparison: with 1m steps you may explore the bumpiness
> of a floor but will not find a hole which has a diameter of 1mm and is
> 10.5m away).
> 

 I have tried several starting Values some quite close to what I thought by
eye might be an okay value (although not brilliant). In that case it just
did one Iteration and then told me that was best it could do, although I am
sure it's not.
The thing is I need a function as simple as possible so its a kind of
step-function in x direction and constant in y direction the parameters are
height, width and offset (although i have tried other functions). All I want
to do with this is find out if there is a bump somewhere in my data which is
straight in y-direction. So the fit is supposed to do really bad if thats
not the case and give back lots of chisquare.
-- 
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