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From: cosimo on 29 Mar 2010 04:42
Hi everibody
i'm a new matlab user... i'm looking for a little help....
i have to solve the coefficients of a quadratic surface passing through nine points of a 3X3 window (in form of a 3X3 matrix) using a linear least squares approximation in a form of
A+Bx+Cy+Dx^2+Exy+Fy^2
and defining a coordinate system with its origin at the centre of the window.

Can i have a quick start?!

Cò.
From: John D'Errico on 29 Mar 2010 06:48
"cosimo " <cosimomartelli(a)hotmail.com> wrote in message <hopp5e$22l$1(a)fred.mathworks.com>...
> Hi everibody
> i'm a new matlab user... i'm looking for a little help....
> i have to solve the coefficients of a quadratic surface passing through nine points of a 3X3 window (in form of a 3X3 matrix) using a linear least squares approximation in a form of
> A+Bx+Cy+Dx^2+Exy+Fy^2
> and defining a coordinate system with its origin at the centre of the window.
>
> Can i have a quick start?!

What are the (x,y) coordinates of each point?

[xc,yc] = meshgrid([-1 0 1],[-1 0 1]);

We need xc and yc as column vectors though. So
unroll them into column vectors.

xc = xc(:);
yc = yc(:);

Do the same with the matrix of function values. Then
call polyfitn, after you download it from the file
exchange. Find it here:

http://www.mathworks.com/matlabcentral/fileexchange/10065

This should get you 90% of the way there. If, as
I suspect, you really need this for homework, then
polyfitn won't help you at all. But then, I won't do
your homework.

John
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