Deformation gradient tensor from coordinate data?

Hi,

I would like to construct the deformation gradient tensor from two set of coordinate data. I have two sets of 3D Cartesian coordinates for a 3x3 grid. The first set is the reference configuration and the second set is the deformed configuration.

In particluar how do I calculate the terms?

Am I right in thinking that terms are the changes in the coords from the reference state to the deformed state? In which case what do the terms represent?

Thanks for any help with this, I feel like I know the answer but for some reason cant see the trees for the woods.

Nic