Polynomial fit in 2 dimensions



[p, S] = polyfit2b(x,y,z,n,m)


Compute the polynomial coefficients of a
function of 2 variables x and y of degrees n and m, respectively,
that fit	the data in z in a robust least-squares sense, using bisquare weights on residuals.
x,y and z can be vectors or matrices of the same size.
S is a structure containing three elements: the Cholesky factor of the
Vandermonde matrix, the degrees of freedom and the norm of the residuals.
if n = 3 and m = 1,
the coefficents of the output p
matrix are arranged as shown:
    p31 p30
    p21 p20
    p11 p10
    p01 p00

The indices on the elements of p correspond to the order of x and y associated with that element.

For a solution to exist, the number of ordered triples [x,y,z] must equal or exceed (n+1)*(m+1). Note that m or n may be zero.

To evaluate the resulting polynominal function, use polyval2D.