| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
| .\" <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
| .\" professionally. |
| .\" |
| .\" Formatted or processed versions of this manual, if unaccompanied by |
| .\" the source, must acknowledge the copyright and authors of this work. |
| .\" %%%LICENSE_END |
| .\" |
| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) |
| .\" Modified 2002-07-27 by Walter Harms |
| .\" (walter.harms@informatik.uni-oldenburg.de) |
| .\" |
| .TH ERF 3 2021-03-22 "GNU" "Linux Programmer's Manual" |
| .SH NAME |
| erf, erff, erfl \- error function |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .PP |
| .BI "double erf(double " x ); |
| .BI "float erff(float " x ); |
| .BI "long double erfl(long double " x ); |
| .PP |
| .fi |
| Link with \fI\-lm\fP. |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR erf (): |
| .nf |
| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .PP |
| .BR erff (), |
| .BR erfl (): |
| .nf |
| _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .fi |
| .SH DESCRIPTION |
| These functions return the error function of |
| .IR x , |
| defined as |
| .TP |
| erf(x) = 2/sqrt(pi) * integral from 0 to x of exp(\-t*t) dt |
| .SH RETURN VALUE |
| On success, these functions return the value of the error function of |
| .IR x , |
| a value in the range [\-1,\ 1]. |
| .PP |
| If |
| .I x |
| is a NaN, a NaN is returned. |
| .PP |
| If |
| .I x |
| is +0 (\-0), +0 (\-0) is returned. |
| .PP |
| If |
| .I x |
| is positive infinity (negative infinity), |
| +1 (\-1) is returned. |
| .PP |
| If |
| .I x |
| is subnormal, |
| a range error occurs, |
| and the return value is 2*x/sqrt(pi). |
| .SH ERRORS |
| See |
| .BR math_error (7) |
| for information on how to determine whether an error has occurred |
| when calling these functions. |
| .PP |
| The following errors can occur: |
| .TP |
| Range error: result underflow (\fIx\fP is subnormal) |
| .\" .I errno |
| .\" is set to |
| .\" .BR ERANGE . |
| An underflow floating-point exception |
| .RB ( FE_UNDERFLOW ) |
| is raised. |
| .PP |
| These functions do not set |
| .IR errno . |
| .\" It is intentional that these functions do not set errno for this case |
| .\" see http://sources.redhat.com/bugzilla/show_bug.cgi?id=6785 |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR erf (), |
| .BR erff (), |
| .BR erfl () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| .PP |
| The variant returning |
| .I double |
| also conforms to |
| SVr4, 4.3BSD. |
| .SH SEE ALSO |
| .BR cerf (3), |
| .BR erfc (3), |
| .BR exp (3) |