(defun set-translation! (out matrix vec)
  "Copy the components of VEC to the translation column of MATRIX. This
destructively modifies MATRIX."
  (with-matrices ((o out)
                  (m matrix))
    (v3:with-vectors ((v vec))
      (copy-rotation! out matrix)
      (psetf o03 vx o13 vy o23 vz o33 m33)))
  out)