bellbind

// erf(x): error function (see: https://en.wikipedia.org/wiki/Error_function)
// by https://github.com/jeremybarnes/cephes/blob/master/cprob/ndtr.c

const P = [
    2.46196981473530512524E-10,
    5.64189564831068821977E-1,
    7.46321056442269912687E0,
    4.86371970985681366614E1,
    1.96520832956077098242E2,
    5.26445194995477358631E2,