If you have a curve fitting toolbox, you can use fit(): https://www.mathworks.com/help/curvefit/fit.html function with fitype chosen from polyij as given here: https://www.mathworks.com/help/curvefit/list-of-library-models-for-curve-and-surface-fitting.html#btbcxlm. For example
x; % x-values 9x1
y; % y-values 9x1
z; % z-values 9x1
X = [x y];
Y = z;
fitted_model = fit(X, Y, 'poly22')
If you don't have the toolbox, you can still use mldivide (\) to do least square curve-fitting. For example, suppose you want to fit following model
Then you can do something like this
X = [ones(size(x)) x y x.^2 y.^2 x.*y];
Y = z;
a = X\Y;
