ERF(3) Library Functions Manual ERF(3)

erf erff erfl — error functions

#include <math.h>

double erf(double x);
float erff(float x);
long double erfl(long double x);

The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 (“POSIX.1”) defers to the ISO C standard.

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 (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

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 () should be returned.

These functions may fail if:

[MX] 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.

None.

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

None.

None.

erfc(3) , feclearexcept(3) , fetestexcept(3) , isnan(3) , the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), xbd_chap04(7), <math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The DESCRIPTION is updated to indicate how an application should check for an error. This text was previously published in the APPLICATION USAGE section.

The erf () function is no longer marked as an extension.

The erfc(3) function is now split out onto its own reference page.

The () and () functions are added for alignment with the ISO/IEC 9899:1999 (“ISO C99”) standard.

The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 (“ISO C99”) standard are marked.

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December 6, 2001 posix.fail