I'm working on a problem where I have to find the little co-group and star of two wave vectors for a diamond structure (space group 227). I know I have to act on the vector by the symmetry operations in the group (perhaps only the ones in the isogonal point group, Oh?) and see if it remains the same or at a point in the reciprocal lattice. My problem is that i dont know how to do it explicitly. How do I find the matrix representations of the operations?