I need to come up with a curve fit $f(w,x,y,z)$ based on 400 tabulated values as shown below. I was thinking of using the functional form
$$ f(w,x,y,z) = \sum_{i=0}^{i=2}\sum_{j=0}^{i=2}\sum_{k=0}^{i=2}\sum_{l=0}^{i=2}a_{ijkl}w^ix^jy^kz^l $$
and determining the 81 values of $a_{ijkl}$ from least squares minimisation.
Can anybody volunteer a better suggestion? Are there any pre-processing tricks that I could exploit? Thanks
