x1       x2      y
 -1       -1       21.6
  1       -1       18.9
 -1        1       20.2
  1        1       16.5
  0        0       24.0
  0        0       22.2
  0        0       23.6
  0        0       25.3
  0        0       24.4
 -1.414    0       22.4
  1.414    0       20.6
  0       -1.414   19.6
  0        1.414   17.9
  0        0       25.0
  0        0       24.1
  0        0       22.2