## Linux and UNIX Man Pages

Test Your Knowledge in Computers #813
Difficulty: Medium
The CSS RGBA alpha parameter defines the opacity as a number between 1.0 (fully transparent) and 0.0 (fully opaque).
True or False?

# erf(3) [centos man page]

```ERF(3)							     Linux Programmer's Manual							    ERF(3)

NAME
erf, erff, erfl, - error function

SYNOPSIS
#include <math.h>

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

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

erf():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
erff(), erfl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

DESCRIPTION
The erf() function returns the error function of x, defined as

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

RETURN VALUE
On success, these functions return 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).

ERRORS
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.

CONFORMING TO
C99, POSIX.1-2001.  The variant returning double also conforms to SVr4, 4.3BSD.

cerf(3), erfc(3), exp(3)

COLOPHON
This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.

GNU								    2010-09-20								    ERF(3)```

## Check Out this Related Man Page

```ERFC(3) 						     Linux Programmer's Manual							   ERFC(3)

NAME
erfc, erfcf, erfcl - complementary error function

SYNOPSIS
#include <math.h>

double erfc(double x);
float erfcf(float x);
long double erfcl(long double x);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

erfc():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
erfcf(), erfcl():
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600|| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

DESCRIPTION
The erfc() function returns the complementary error function of x, that is, 1.0 - erf(x).

RETURN VALUE
On success, these functions return the complementary error function of x, a value in the range [0,2].

If x is a NaN, a NaN is returned.

If x is +0 or -0, 1 is returned.

If x is positive infinity, +0 is returned.

If x is negative infinity, +2 is returned.

If the function result underflows and produces an unrepresentable value, the return value is 0.0.

If the function result underflows but produces a representable (i.e., subnormal) value, that value is returned, and a range error occurs.

ERRORS
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 (result is subnormal)
An underflow floating-point exception (FE_UNDERFLOW) is raised.

These functions do not set errno.

CONFORMING TO
C99, POSIX.1-2001.  The variant returning double also conforms to SVr4, 4.3BSD.

NOTES
The erfc() functions are provided to avoid the loss accuracy that would occur for the calculation 1-erf(x) for large values of x (for which
the value of erf(x) approaches 1).