"Input argument is undefined" when using nlinfit
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Despite the variables all being defined in the workspace, implementation of the nlinfit function returns the error "Input argument p is undefined". The code I used follows:
fun = @(b,x,y,p) b(1).*x.*p.*((y/x).^b(2) - 1) + b(3)
b0 = [1 1 1];
mdl = nlinfit([x y p],q,fun, b0)
b0 gives the initial values for the coefficients to be determined - b1,b2,b3. fun is an anonymous function according to which the data is to be fit. x,y,p,q are all column vectors, which are visible in the workspace. Any help as to what is going on here would be greatly appreciated. Thank you very much in advance.
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the cyclist
2014-5-27
Something like this?
x = rand(100,1);
y = rand(100,1);
p = rand(100,1);
q = rand(100,1);
M = [x y p];
fun = @(b,M) b(1).*M(:,1).*M(:,3).*((M(:,2)./M(:,1)).^b(2) - 1) + b(3)
b0 = [1 1 1];
mdl = nlinfit(M,q,fun, b0)
3 个评论
Gautam
2014-5-27
the cyclist
2014-5-27
编辑：the cyclist
2014-5-27
Because nlinfit is only passing one variable [the matrix I defined as M, (called "X" in the documentation)] to fun(). In the syntax you used, MATLAB has no way of knowing that the array
[x,y,p]
should be parsed into the three separate variables of your function.
Gautam
2014-5-28
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