Why do my coeffvalues not produce a sensible result?
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I have a script that uses the fit fuction on some data using a poly55 fit type. I then use this to get the coeffvalues for the fittted curve and try to replot the surface using the coeffvalues but the result produced is orders of magnitude different from the original data.
Script attached as well as some example data.
Can anyone explain what is happening or recommend a way forward?
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Accepted Answer
Torsten
on 28 Aug 2019
If you use the 'Normalize','on' fitting option, your polynomial has powers of (x-meanx)/stdx and (y-meany)/stdy instead of x and y.
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Torsten
on 28 Aug 2019
if you switch the mentioned option off, you can use the polynomial you defined in the calculation.
Otherwise you will have to insert (x-meanx)/stdx for x and (y-meany)/stdy for y in the calculation for your polynomial value:
f(x,y) = p00 + p10*(x-meanx)/stdx + p01*(y-meany)/stdy + p20*((x-meanx)/stdx))^2 + ...
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