---- sequential ----
  factor A = L*D*L' time: 11.1376 sec
  solve A*X=B time: 20.9472 sec
  |A*X-B| = 2.06205e-09

---- parallel ----
  factor A = L*D*L' time: 1.04306 sec
  solve A*X = B time: 2.46214 sec
  |A*X-B| = 1.17805e-09

