Simple multidimensional curve fitting

Question

I have a bunch of data, generally in the form a, b, c, ..., y

where y = f(a, b, c...)

Most of them are three and four variables, and have 10k - 10M records.

Answer 1

There's a tool for fitting 1D and 2D curves at zunzun.com, but I don't think it goes beyond two variables. Likewise, Matlab doesn't support more than two dimensions fitting (as far as I know) and it's certainly not free.

Otherwise, you might be able to find part of your solution in the Numerical Recipes.

But as other posters indicated, you'll probably need at least a basic idea of your function model (which, hopefully, is linear or can be linearized, in which case you'll have a much larger array of solutions at your disposal)