MATLAB: Fitting data using polyfit, nlfit

nlfitpolyfit

I have 2 sets of data of the same size (X1, Y1) and (X2,Y2). (X1,Y1) has a linear relationship with zero intercept (Y1=slope*X1). How can I estimate the slope, R^2 value and plot it along with 95% confidence interval lines? Using Corrcoeff, polyfit and polyval gives me a relationship of the form Y1=slope*X1 + c, but I would like to force c=0.
(X2,Y2) has a non-linear relationship of the form Y2=A-Bexp(C*X2). Likewise, I would like to determine A,B & C along with R^2 value and plot it along with 95% confidence interval lines. I know I have to use nlinfit, nlparci but I am new in this and would need your help.
Thanks much.

Best Answer

You seem to be acquainted with nlinfit and know how to use it, but apparently not with Anonymous Functions.
I suggest you use nlinfit for both problems. With B = [B(1) ... B(n)]' a column vector of parameters, your Y1 function becomes:
Y1 = @(B,x) B.*x;
since with only one parameter in it, you do not need to use subscripts.
Your Y2 function becomes:
Y2 = @(B,x) B(1)-B(2).*exp(B(3).*x);
These should work as your modelfun functions in nlinfit.
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