Function of 4 inputs f(a,b,c,d) = K. I have the inputs and K for a number of equations. How do I find the f()?

There's a certain model that takes 4 known but varying inputs and pumps out a constant. This is done over many observation periods. So I have a bunch of equations, I know what all the inputs and the answers are, but how do I find the equation that turns the inputs into the answer, i.e. the function? I've tried matrix multiplication on a 4x4 but it gives close answers not very exact....

Function of 4 inputs f(a,b,c,d) = K. I have the inputs and K for a number of equations. How do I find the f()?
Try ax+by+cz+dw=k


Write 4 equations using values of x,y,z and w from your data.


Solve the simultaneous four equations as you did using a 4x4 matrix. and get the values of a,b,c, and d. That will be your equation.