# ERF

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

SEE ALSO

COLOPHON

## NAME

erf, erff,
erfl, − error function

## SYNOPSIS

**#include
<math.h>**

**double
erf(double** *x***); **

float erff(float *x***); **

long double erfl(long double *x***);**

Link with
*−lm*.

Feature Test
Macro Requirements for glibc (see
**feature_test_macros**(7)):

**erf**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

**erff**(),
**erfl**():

_BSD_SOURCE || _SVID_SOURCE ||
_XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;

or *cc -std=c99*

## DESCRIPTION

The
**erf**() function returns the error function of
*x*, defined as

erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(−t*t)
dt

## RETURN VALUE

On success,
these functions return the error function of *x*, a
value in the range [−1, 1].

If *x* is
a NaN, a NaN is returned.

If *x* is
+0 (−0), +0 (−0) is returned.

If *x* is
positive infinity (negative infinity), +1 (−1) is
returned.

If *x* is
subnormal, a range error occurs, and the return value is
2*x/sqrt(pi).

## ERRORS

See
**math_error**(7) for information on how to determine
whether an error has occurred when calling these
functions.

The following
errors can occur:

Range error: result underflow (*x* is subnormal)

An underflow floating-point
exception (**FE_UNDERFLOW**) is raised.

These functions
do not set *errno*.

## ATTRIBUTES

For an
explanation of the terms used in this section, see
**attributes**(7).

## CONFORMING TO

C99,
POSIX.1-2001. The variant returning *double* also
conforms to SVr4, 4.3BSD.

## SEE ALSO

**cerf**(3),
**erfc**(3), **exp**(3)

## COLOPHON

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