erf(3) Library Functions Manual erf(3) NAME erf, erff, erfl - error function LIBRARY Math library (libm, -lm) SYNOPSIS #include 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(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE erff(), erfl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE DESCRIPTION These functions return 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 value of 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. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). +--------------------------------------------+---------------+---------+ |Interface | Attribute | Value | +--------------------------------------------+---------------+---------+ |erf (), erff (), erfl () | Thread safety | MT-Safe | +--------------------------------------------+---------------+---------+ STANDARDS C11, POSIX.1-2008. HISTORY C99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD. SEE ALSO cerf(3), erfc(3), exp(3) Linux man-pages 6.9.1 2024-05-02 erf(3)