Error function approximation via the Abramowitz & Stegun formula.
erf(x) = 1 - (a₁·t + a₂·t² + a₃·t³ + a₄·t⁴ + a₅·t⁵) × exp(-x²) where t = 1/(1 + p·|x|), p = 0.3275911
Maximum absolute error: 1.5 × 10⁻⁷.
Error function approximation via the Abramowitz & Stegun formula.
erf(x) = 1 - (a₁·t + a₂·t² + a₃·t³ + a₄·t⁴ + a₅·t⁵) × exp(-x²) where t = 1/(1 + p·|x|), p = 0.3275911
Maximum absolute error: 1.5 × 10⁻⁷.