Get function handle of fit function in matlab and assign fit parameters

问题

I'm fitting custom functions to my data. After obtaining the fit I would like to get something like a function handle of my fit function including the parameters set to the ones found by the fit. I know I can get the model with

formula(fit) 

and I can get the parameters with

coeffvalues(fit) 

but is there any easy way to combine the two in one step?

回答1:

This little loop will do the trick:

x = (1:100).';  %'
y = 1*x.^5 + 2*x.^4 + 3*x.^3 + 4*x.^2 + 5*x + 6;
fitobject = fit(x,y,'poly5');  

cvalues = coeffvalues(fitobject);
cnames = coeffnames(fitobject);
output = formula(fitobject);

for ii=1:1:numel(cvalues)
    cname = cnames{ii};
    cvalue = num2str(cvalues(ii));
    output = strrep(output, cname , cvalue);
end

output = 1*x^5 + 2*x^4 + 3*x^3 + 4*x^2 + 5*x + 6

The loop needs to be adapted to the number of coefficients of your fit.

Edit: two slight changes in order to fully answer the question.

fhandle = @(x) eval(output)

returns a function handle. Secondly output as given by your procedure doesn't work, as the power operation reads .^ instead of x, which can obviously be replaced by

strrep(output, '^', '.^');

回答2:

You can use the Matlab curve fitting function, polyfit.

p = polyfit(x,y,n)

So, p contains the coefficients of the polynomial, x and y are the coordinates of the function you're trying to fit. n is the order of the polynomial. For example, n=1 is linear, n=2 is quadratic, etc. For more info, see this documentation centre link. The only issue is that you may not want a polynomial fit, in which case you'll have to use different method.

Oh, and you can use the calculated coefficients p to to re-evaluate the polynomial with:

f = polyval(p,x);

Here, f is the value of the polynomial with coefficients p evaluated at points x.

来源：https://stackoverflow.com/questions/16478077/get-function-handle-of-fit-function-in-matlab-and-assign-fit-parameters