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erf

Error function.

SYNOPSIS:

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

DESCRIPTION:

The integral is
                           x
                            -
                 2         | |          2
   erf(x)  =  --------     |    exp(- t) dt.
              sqrt(pi)   | |
                          -
                           0

The magnitude of x is limited to 9.231948545 for DEC arithmetic; 1 or -1 is returned outside this range.
For 0 <= |x| < 1, erf(x) = x * P4(x**2)/Q5(x**2); otherwise erf(x) = 1 - erfc(x).

ACCURACY:
                      Relative error:
arithmetic   domain     # trials      peak         rms
    DEC       0,1         14000       4.7e-17     1.5e-17
    IEEE      0,1         30000       3.7e-16     1.0e-16