Matlab nonlinear regression

2011 3 14
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I have never used matlab, and i need help with a nonlinear regression problem, ive looked up the nlinfit funtction help but I dont understand it a lot.
I have mi I data, and my V data. i have my plot. Now im supposed to do an nonlinear regression as far as i understand thi is my function
I(V)=Ix-Ix(V/Vx)^(n+q) I know I and V but i need to find Ix,(n+q) and V. I'll appreciated if someone can help out.

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Matt Tearle
Matt Tearle 2011-3-14

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You need to make a function of two variables b and V. The three elements of b are the three unknowns lx, (n+q), and Vx. Note that, as given, there's no way to determine n and q individually, only the sum. Once you have the function foo(b,V), pass that to nlinfit, with an initial guess at b
b = nlinfit(Vdata,Idata,@foo,[pi;42;0])

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ChrisGonzVilla
ChrisGonzVilla 2011-3-15
Thanks!!
That's the problem im having i dont know how to make that new function, is it the same as the original function that im using?
ChrisGonzVilla
ChrisGonzVilla 2011-3-15
V = [0.53 0.53 0.53 0.52 0.52 0.52 0.51 0.49 0.49 0.48 0.45 0.38 0.37 0.36 0.34 0.34 0.27 0.19 0.03 0.02]';
I = [0.002 0.003 0.003 0.006 0.011 0.022 0.051 0.098 0.125 0.16 0.22 0.38 0.41 0.45 0.49 0.55 0.67 0.69 0.69 0.717]';
This is my data, and i want to make a fit of this plot, this is my assignment, dont understand how to create this new function.

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