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erfc

Complementary error function.

SYNOPSIS:

double x, y, erfc();
y = erfc(x);

DESCRIPTION:

  1 - erf(x) =
                           inf.
                             -
                  2         | |          2
   erfc(x)  =  --------     |    exp(- t) dt
               sqrt(pi)   | |
                           -
                            x

For small x, erfc(x) = 1 - erf(x); otherwise rational approximations are computed.
A special function expx2.c is used to suppress error amplification in computing exp(-x^2).

ACCURACY:
                     Relative error:
arithmetic   domain     # trials      peak         rms
   IEEE      0,26.6417   30000       1.3e-15     2.2e-16

ERROR MESSAGES:

  message         condition            value returned
  underflow    x > 9.231948545 (DEC)       0.0