-- stackoverflow.com/questions/27229371/inverse-error-function-in-c

-- f(x) is inverse erf

f(x) = test(x <= -1.0, -10.0, x >= 1.0, 10.0, f1(x))

f1(x,p,t) = do(
 t = log(1 - x^2),
 test(abs(t) > 6.125,
  do(
  p =       3.03697567 10.0^(-10),
  p = p t + 2.93243101 10.0^(-8),
  p = p t + 1.22150334 10.0^(-6),
  p = p t + 2.84108955 10.0^(-5),
  p = p t + 3.93552968 10.0^(-4),
  p = p t + 3.02698812 10.0^(-3),
  p = p t + 4.83185798 10.0^(-3),
  p = p t - 2.64646143 10.0^(-1),
  p = p t + 8.40016484 10.0^(-1)),
  do(
  p =       5.43877832 10.0^(-9),
  p = p t + 1.43285448 10.0^(-7),
  p = p t + 1.22774793 10.0^(-6),
  p = p t + 1.12963626 10.0^(-7),
  p = p t - 5.61530760 10.0^(-5),
  p = p t - 1.47697632 10.0^(-4),
  p = p t + 2.31468678 10.0^(-3),
  p = p t + 1.15392581 10.0^(-2),
  p = p t - 2.32015476 10.0^(-1),
  p = p t + 8.86226892 10.0^(-1))
 ), -- end of test
 p x -- return value
)

"Max error"

m = 0
for(k, -1000, 1000,
 x = 0.001 k,
 t = abs(erf(f(x)) - x),
 test(t > m, do(m = t, y = x))
) -- end of for loop
m
y