Hi All, I have some problems in figuring out a solution for an issue I am trying to solve. I have a 3D grid of dimension Nx, Ny, Nz; for every cell of this grid, I calculate the cell centroids (with the cell coordinates x, y, and z) and then I try to find which cell centroid is the closest to a specified point in 3D (which I supply). I still haven't figured out how to do this, even if I have some ideas (and suggestions for this problem are welcome :-D ). But the problem is another one. When I find the closest centroid, I know only the cell ID of this centroid. The cell ID is (usually) defined as: ID = (K-1)*Nx*Ny + (J-1)*Nx + I - 1 Where I, J, K are the cell indexes. Now, the problem is, how can I calculate back the I, J, K indexes knowing only the cell ID? I am trying to solve this using numpy (as my grid is stored using a numpy array), but it's something akin to the Matlab function ind2sub... Thank you for your suggestions. Andrea. "Imagination Is The Only Weapon In The War Against Reality." http://xoomer.alice.it/infinity77/