Legacy Document

erf

You can use the erf function to perform the error function.

double_t erf (double_t x);

x

Any floating-point number.

DESCRIPTION

The erf function computes the error function of its argument. This function is antisymmetric.

$erf(x)\; =\; 2\; OVER\; pi$₀^xe^(-t)2dt

EXCEPTIONS

When x is finite and nonzero, either the result of erf(x) is exact or it raises one of the following exceptions:

• inexact (if the result must be rounded or an underflow occurs)
• underflow (if the result is inexact and must be represented as a denormalized number or 0)

SPECIAL CASES

Table 10-35 shows the results when the argument to the erf function is a zero, a NaN, or an Infinity.

Special cases for the erf function

Operation	Result	Exceptions raised
$erf(+0)$	+0	None
$erf(-0)$	$-0$	None
$erf(NaN)$	NaN	None[59]
$erf(+$ )	+1	None
$erf(-$ )	-1	None

EXAMPLES

z = erf(1.0);     /* z  0.842701. The inexact exception is 
                     raised. */
z = erf(-1.0);    /* z  -0.842701. The inexact exception is 
                     raised. */

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[59] If the NaN is a signaling NaN, the invalid exception is raised.