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how to extract the formula from fit function?

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Amin Tehrani
Amin Tehrani 2017-11-29
评论： Walter Roberson 2024-4-16
I want to use fit function to get the formula with its coefficient for my data. so i have used: [curve, goodness, output] = fit(fk,Rfft,'linearinterp'); in case of 'poly1' or 'poly2' the curve variable (which is in cfit format) shows the formula with its coefficients however when i use linearinterp the curve does not show the formula, it just says "piecewise polynomial". i need to get the formula with its coefficients. does anyone have any idea how to get the formula?
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采纳的回答

Vishwas
Vishwas 2017-12-7
There really isn't a formula for the surface. It's a piecewise linear surface so it's a single formula for a plane at each location of your data making it many formulas altogether.

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Bowen Song
Bowen Song 2019-3-16
编辑：Bowen Song 2019-3-16
Treat it as a string... lol check this out
[fitresult{1}, gof(1)] = fit( [xData, yData], zData, ft );
... from above you get your sfit or what not
f = string(formula(fitresult{1})); // get the formular in string format
names = coeffnames(fitresult{1}); // get the coeff names
vals = coeffvalues(fitresult{1}); // get those values
for i = 1:length(names)
f = strrep(f,string(names(i)),string(vals(i))); // replace the coeff names with values
end
eval(f) // muhaha
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Xiyan Li
Xiyan Li 2024-4-16
I wonder how to get the equation out after piecewise fitting? It makes no sense to me without gettting the equation out.
Walter Roberson
Walter Roberson 2024-4-16
@Xiyan Li
The output is a piecewise polynomial. It does not have a single equation. It is effectively a list of equations that are each valid over a specific range.

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