erf, erff, erfl - error function

```
#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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

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

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).

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`

.

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

Interface | Attribute | Value |

erf(), erff(), erfl() | Thread safety | MT-Safe |

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

The variant returning `double`

also conforms to SVr4, 4.3BSD.

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