erf(3) Library Functions Manual erf(3)

# NAME

erf, erff, erfl - error function

# LIBRARY

Math library (libm, -lm)

# SYNOPSIS

`#include <math.h>`
```double erf(double x);
float erff(float x);
long double erfl(long double x);```
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

erf():

```
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE```

erff(), erfl():

```
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE```

# DESCRIPTION

These functions return 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 value of 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:

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).

 Interface Attribute Value erf (), erff (), erfl () Thread safety MT-Safe

# STANDARDS

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD.