G7a tri_pgs --axis=2 --no-stop: it, KE_np1, KE_np2, |dKE|/KE_np1, KE_np2 <= KE_np1 (1+1e-6); <= 1e-3 at 16, <= 1e-5 at 64
    4 0.1042666 0.1006088 3.508e-02 True
    8 0.1042415 0.1038624 3.637e-03 True
   16 0.1042415 0.104235 6.292e-05 True ok
   32 0.1042415 0.1042415 1.410e-07 True
   64 0.1042415 0.1042415 1.410e-07 True ok
G7c cluster_pgs --steps=1 --no-stop: it 8/32/128/256, RMS |v_np - v_np1(same N)| / |v|; non-increasing, <= 1e-3 at 256
  np 2: 1.320e-01 3.960e-02 7.787e-04 4.551e-05 ok
  np 4: 1.714e-01 6.333e-02 3.178e-03 1.014e-04 ok
  np 8: 2.203e-01 8.046e-02 3.555e-03 1.195e-04 ok
G7e ovl (max over steps), ratio to np 1; hard <= 3 x np1 (S18), ratio reported
  cluster: np1 2.704e-02 | np2 4.495e-02 (1.66x) | np4 4.534e-02 (1.68x) | np8 5.234e-02 (1.94x)
  cluster_pgs: np1 2.194e-02 | np2 4.241e-02 (1.93x) | np4 4.962e-02 (2.26x) | np8 4.963e-02 (2.26x)
  cluster_friction: np1 2.060e-02 | np2 4.173e-02 (2.03x) | np4 5.211e-02 (2.53x) | np8 5.233e-02 (2.54x)
G7f ITERS ratio npN / np1 (hard: np2 <= 3.5, np4/8 <= 5)
  pos: np1 96 | np2 157 (1.64x) | np4 157 (1.64x) | np8 233 (2.43x)
  vel: np1 116 | np2 150 (1.29x) | np4 202 (1.74x) | np8 203 (1.75x)
