# erff (3p) - Linux Manuals

## erff: error functions

## PROLOG

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.## NAME

erf, erff, erfl - error functions

## SYNOPSIS

**#include <math.h>
**

**
double erf(double** *x***);
float erff(float**

*x*

**);**

long double erfl(long double

long double erfl(long double

*x*

**);**

## DESCRIPTION

These functions shall compute the error function of their argument
*x*, defined as:

An application wishing to check for error situations should set *errno*
to zero and call
*feclearexcept*(FE_ALL_EXCEPT) before calling these functions.
On return, if *errno* is non-zero or
*fetestexcept*(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.

## RETURN VALUE

Upon successful completion, these functions shall return the value of the error function.

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

If *x* is ±0, ±0 shall be returned.

If *x* is ±Inf, ±1 shall be returned.

If *x* is subnormal, a range error may occur, and 2 * *x*/
*sqrt*(pi) should
be returned.

## ERRORS

These functions may fail if:

- Range Error
- The result underflows.

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
then *errno* shall be set to [ERANGE]. If the
integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
then the underflow floating-point exception shall be
raised.

*The following sections are informative.*

## EXAMPLES

## APPLICATION USAGE

Underflow occurs when |*x*| < DBL_MIN * ( *sqrt*(pi)/2).

On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

## RATIONALE

## FUTURE DIRECTIONS

## COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

## SEE ALSO

*erfc*(), *feclearexcept*(), *fetestexcept*(), *isnan*(),
the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, *<math.h>*