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function p = poly2fit(x,y,z,n)
% POLY2FIT POLY2FIT(x,y,z,n) finds the coefficients of a two-dimensional
% polynomial formed from the data in the matrices x and y
% that fits the data in the matrix z in a least-squares sense.
% The coefficients are returned in the vector p, in descending
% powers of x and y. For example, the second order polynomial
%
% x ^ 2 + xy +2x -3 y - 1
%
% would be returned as p = [ 1 1 0 2 -3 -1 ]
%
% Written my Jim Rees, 12 Aug. 1991
if any((size(x) ~= size(y)) | size(x) ~= size(z))
error('X,Y, and Z matrices must be the same size')
end
% First straighten out x, y, and z.
x = x(:); y = y(:); z = z(:);
n = n+1;
k = 1;
%A = zeros(x);
for i = n:-1:1,
for j=1:i,
A(:,k) = ((x.^(i-j)).*(y.^(j-1))) ;
k = k + 1;
end
end
p = (A\z).';
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