Re: Problem of polyfit

[Tetsuro KURITA]

>  p = inv(X'*X)*X'*y
>    = inv(X)*inv(X')*X'*y
>    = inv(X)*I*y
>    = inv(X)*y
>    = X \ y
>
> wpolyfit does the same with weighting on y, except that it uses QR 
> decomposition to solve X \ y.

In generaly,

inv(a*b) \= inv(b)*inv(a)

If both of a and b are nonsingular matrixes, the following equation is 
right.
inv(a*b) = inv(b)*inv(a)

Acutually, in some case, polyfit.m give bad result.

=======================================================
 Tetsuro KURITA
  E-mail: address@hidden
=======================================================



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