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# Technical Reference: Base Operating System and Extensions, Volume 1

## erf, erff, or erfl Subroutine

### Purpose

Computes the error and complementary error functions.

### Libraries

IEEE Math Library (libm.a)

or
System V Math Library (libmsaa.a)

### Syntax

#include <math.h>

`double erf ( x)`

double x;

float erff (x)
float x;

long double erfl (x)
long double x;

### Description

The erf, erff, and erfl subroutines return the error function
of the x parameter, defined for the erf subroutine as the following:

erf(x) = (2/sqrt(pi) * (integral [0 to x] of exp(-(t**2)) dt)

erfc(x) = 1.0 - erf(x)

Note

Compile any routine that uses subroutines from the

libm.a library with the

-lm flag. To compile the

erf.c file, for example, enter:

cc erf.c -lm

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

### Parameters

x |
Specifies a double-precision floating-point value. |

### Return Values

Upon successful completion, the erf, erff, and erfl subroutines return the value of
the error function.

If x is NaN, a NaN is returned.

If x is ±0, ±0 is returned.

If x is ±Inf, ±1 is returned.

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

### Related Information

erfc, erfcf, or erfcl Subroutine, exp, expf, or expl Subroutine, feclearexcept Subroutine, fetestexcept Subroutine, and class, _class, finite, isnan, or unordered Subroutines.

The sqrt, sqrtf,
or sqrtl Subroutine in AIX 5L Version 5.2 Technical Reference: Base Operating System and Extensions Volume 2.

Subroutines Overview in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.

128-Bit long double Floating-Point
Format in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.

math.h in AIX 5L Version 5.2 Files Reference.

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