title: Get equation for 3d shape
body: <p>I have 2 arrays say X and Y. Each have 5 elements. Now for each possible combination of (X,Y) I have a Z value, so Z is a 5x5 matrix. </p>
  
  <p>I am looking to find a formula e.g. z=f(x,y). Any idea about how that can be done. </p>
  
  <p>I tried MS Excel surface chart, but it doesn't give any equation or curve fitting on surface charts.</p>