erf, erfc

Purpose

     Computes the error and complementary error functions.

Library

     Math Library (libm.a)

Syntax

     #include <math.h>

     double erf (x)                            double erfc (x)
     double x;                                 double x;
     Description

     The  erf  subroutine returns  the  error  function of  x,
     defined as:   (2 / sqrt(&pi.)) times the integral  from 0
     to x of e(-t(2)) dt

     The erfc subroutine returns 1.0 - erf(x).  The erfc  sub-
     routine is provided because of  the extreme loss of rela-
     tive accuracy if  erf(x) is called for large  values of x
     and the result  is subtracted from 1.0.   For example, 12
     decimal places are lost when calculating (1.0 - erf(5)).

     Related Information

     In this book:  "exp, log, log10, pow, sqrt."