# How i can find the formula from an linear interpolation in cftool.

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Benjamin on 5 Nov 2013
Commented: Benjamin on 11 Nov 2013
Hello,
I have 3 set of data. I use cftool, to make an interpolation of theses, and I want to know the formula of the surface.
I use interpolant linear method.
And I have a nice surface on answer and this :
Linear interpolant : f(x,y) = piecewise lenar surface computed from p where x is normalized by mean 551.1 and std 72.04 and where y is normalized by mean 1.499 and std 0.9631
Coefficients : p = coefficient structure
Goodness of fit: SEE : 4.093e+09 R-square : 0.9979 Adjusted R-square : Nan RMSE: Nan
My goal is to have the formula of the surface, like that I can find the third parameter when I know 2 of them.
Thank you
*

Sean de Wolski on 5 Nov 2013
There really isn't a formula for the surface. It's a piecewise linear surface so it's a single formula for a plane at each location of your data making it many formulas altogether.
It sounds like you want to fit a plane or a custom equation to your data so that you can find the coefficients.
Benjamin on 11 Nov 2013
Ok thank you