Hi all
I m given a point P  in 3-D , (x,y,z ) values. And its 8 connecting points ( 3-D points.... (x,y,z) values)  i.e. these 9 points can be considered to be placed in the form of a 3x3 matrix. I have to find the gradient of the plane containing this 9 points at the (2,2) pt P (mid point of the 3x3 matrix). 

I tried to use the sobel kernal type weighted summation of the difference of the points and then divide it by dx (or dy) but that didnt work out. I am considering that the z value of the (x,y,z) values as the function value.... z=f(x,y).

I am not sure if matlab has an inbuilt function for this.
Can anybody please help me with this?

Thanks  
Chandrajit