Re: Problem of polyfit

[Fredrik Lingvall]

Tetsuro KURITA wrote:

> Also following two equations do not return same results, when  
> calculating data I posted.
>
>   p = inv(X'*X)*(X'*y);
>
>   p = (X'*X)\(X'*y);
>
> In the case of data I posted, first equation give better results. It  
> looks that the operator "\" have a certain limitation. What is that ? 

Can you post the output of  norm( inv(X'*X)*X'*y - (X'*X)\X'*y )?

A simple test on my machine:

octave:26> X=randn(100,100);
octave:27> y=randn(100,1);
octave:28> norm( inv(X'*X)*X'*y - (X'*X)\X'*y )
ans =  3.7190e-13

Fredrik



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