@pimms.value<EOL><INDENT>def vertex_normals(face_normals, tess):<DEDENT>
tmp = np.array([np.sum(face_normals[:,fs], axis=<NUM_LIT:1>) for fs in tess.vertex_faces]).T<EOL>norms = np.sqrt(np.sum(tmp ** <NUM_LIT:2>, axis=<NUM_LIT:0>))<EOL>wz = np.isclose(norms, <NUM_LIT:0>)<EOL>return pimms.imm_array(tmp * (np.logical_not(wz) / (norms + wz)))<EOL>
mesh.vertex_normals is the (3 x n) array of the outward-facing normal vectors of each
  vertex in the given mesh. If mesh is a 2D mesh, these are all either [0,0,1] or
  [0,0,-1].