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FindFit question - find multiple solutions in one run?

Posted 10 years ago
Dear all,

is there a way that FindFit gives all the possible values for the specified parameters?

For example, in the file at the url http://www.risc.jku.at/people/merascu/FindFit.nb, I should basically have 4 values for each of the parameters a and b (3 for each a and b determining the the curves, and 1 a and 1 b for the isolated point at the left most of the graphic).
If is not possible with FindFit, is there another way?

Thanks
POSTED BY: Madalina Erascu
2 Replies
If you generate the equations describing the fitting parameters, you could try solving them with FindRoot, using multiple starting points.  Given the number of data points, I don't think that NSolve would be able to handle the problem.
POSTED BY: Frank Kampas
In the ListPlot it looks like you have data points falling along several curves. What you really have is a flat list of data points and what looks like curves are not made up of sequential points, but are quite interlaced together. Have a look at the same ListPlot with the option Joined -> True
ListPlot[lstQ, ImageSize -> {1200, 339}, AspectRatio -> Full , Joined -> True, PlotRange -> All]
The data list can be split up this way into four separate runs of data. The resulting split is not perfect.
ListPlot[Transpose[Partition[lstQ, 4, 4]], ImageSize -> {1200, 339}, AspectRatio -> Full , Joined -> True, PlotRange -> All]
I think that the fitting functions will not be happy, till the data for a single curve can be isolated out. Then you can fit the three or four separately.
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