it would be very nice if someone could help me with this problem.
I have a set of 5 points in space with x, y, z coordinates and I would like to fit them with a surface. Generally I use fitsurf setting the option 'poly22' to get the equation in the secondo order of x and y.
Now I would like to fit them with the equation f(x,y) = ax + by + cxy + d . Is there a way to do it? Can we set the custom equation using fitsurface?
Thank you very much in advance for your answers!