Very simple function to find the 26 (or less if near the borders) neighbouring indices of an voxel in a 3-D volume given it's index position, which can be useful for image processing. I thought this was a built in function in Matlab but it does not appear to be, so maybe this saves you some time.
Use the sub2ind function to get the index position of the i,j,k voxel
just edited my comments
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