Hi Danilo,
Try using the curve fitting toolbox.
Here is the link to:
load franke
f = fit( [x, y], z, 'poly23' )
plot(f, [x,y], z)
Gives the nice answer of:
Linear model Poly23:
f(x,y) = p00 + p10*x + p01*y + p20*x^2 + p11*x*y + p02*y^2 + p21*x^2*y +
p12*x*y^2 + p03*y^3
Coefficients (with 95% confidence bounds):
p00 = 1.118 (0.9149, 1.321)
p10 = -0.0002941 (-0.000502, -8.623e-005)
p01 = 1.533 (0.7032, 2.364)
p20 = -1.966e-008 (-7.084e-008, 3.152e-008)
p11 = 0.0003427 (-0.0001009, 0.0007863)
p02 = -6.951 (-8.421, -5.481)
p21 = 9.563e-008 (6.276e-009, 1.85e-007)
p12 = -0.0004401 (-0.0007082, -0.0001721)
p03 = 4.999 (4.082, 5.917)
I hope that this helps you.
Gareth
