What Format Equation do the Output Coefficients For fit2dPolySVD Do 4th, 6th and 8th Order Solutions Go To?

The outputs for this function are coefficients to an equation, if you chose a 2nd order fit then you can use the equation provided in the example (shown in the link below), but if you want to do a 4th, 6th, 8th order equation it is not clear to me what equation format the coefficients will go to. Please provide the equation that the output coefficients would go to for a 4th, 6th, and 8th order solution.

http://www.mathworks.com/matlabcentral/fileexchange/31636-2d-polynomial-fitting-with-svd/content/fit2dPolySVD.m

Thanks,

-Ryan