Complementary error function, erfc(x) = 1 - erf(x), accurate in the upper tail (down to the subnormal range near
x = 27).
Not an R function. R writes it as 2 * pnorm(x * sqrt(2), lower.tail = FALSE).
Parameters
a: number
Argument.
Returns number
erfc(a).
Example
erfc(5); // 1.537459794428035e-12
Changes from xsf: exp(-x^2) is formed from x^2 = hi + lo exact (the rounding of x^2 is 33 ε relative at x = 5.7),
and below the normal range exp(-700) is applied last so that subnormal results (x up to 27.2) are not flushed to 0.
Complementary error function, erfc(x) = 1 - erf(x), accurate in the upper tail (down to the subnormal range near x = 27). Not an R function. R writes it as
2 * pnorm(x * sqrt(2), lower.tail = FALSE).