# erf(3M)

**erf, erfc --
error functions
**

## Synopsis

cc [*flag* ...] *file* ... -lm [*library* ...]
#include <math.h>

double erf(double *x*);

float erff(float *x*);

long double erfl(long double *x*);

double erfc(double *x*);

float erfcf(float *x*);

long double erfcl(long double *x*);

## Description

**erf**, **erff** and **erfl**
return the error function of
*x*, defined as:

**erfc**, **erfcf** and **erfcl**
return 1.0 - **erf**(*x*). They are provided
because of the extreme loss of relative accuracy when
**erf**(*x*) is called for large *x*
and the result is subtracted from 1.0 (for example, for
*x* = 5, 12 places are lost).

### Errors

On systems that support IEEE **NaN**, if *x* is a quiet
**NaN**, that value is returned. If *x* is a signaling
**NaN**, a quiet **NaN** is returned
and the invalid operation exception is raised.
In either case, **errno** is set to **EDOM**.
In the **-Xt** compilation mode,
the error handling procedures may be changed with the function
**matherr**.

## References

**matherr**(3M)

*
© 2004 The SCO Group, Inc. All rights reserved.
*

UnixWare 7 Release 7.1.4 - 25 April 2004