erf, erfc - error function and complementary error func
tion
#include <math.h>
double erf(double x);
double erfc (double x);
The erf() function returns the error function of x;
defined as
erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(-t*t) dt
The erfc() function returns the complementary error func
tion of x, that is 1.0 - erf(x).
SVID 3, BSD 4.3
exp(3)