2. Second, we decomposed the four massive particles of the decoupled topology involved in the two coupled triangles using eq 7 to find the matrix D and vectors qi . Then, we generated U ∈ SO( ) such that it corresponded to a random four-dimensional rotation by a small angle. The application of DU to qi produced new homogeneous coordinate vectors r i and hence provided new positions r i and masses m i . Following Laus and Selig, this procedure guaranteed that M , R, and X remained fixed.