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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
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.\" Modified 2002-07-27 by Walter Harms
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.\" (walter.harms@informatik.uni-oldenburg.de)
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.\"
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.TH ERF 3 2008-08-05 "GNU" "Linux Programmer's Manual"
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.SH NAME
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erf, erff, erfl, \- error function
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.SH SYNOPSIS
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.nf
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.B #include <math.h>
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.BI "double erf(double " x );
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.BI "float erff(float " x );
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.BI "long double erfl(long double " x );
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.fi
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Link with \fI\-lm\fP.
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR erf ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.br
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.BR erff (),
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.BR erfl ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 600|| _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.ad b
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.SH DESCRIPTION
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The
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.BR erf ()
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function returns the error function of \fIx\fP, defined
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as
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.TP
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erf(x) = 2/sqrt(pi)* integral from 0 to x of exp(\-t*t) dt
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.SH RETURN VALUE
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On success, these functions return the error function of
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.IR x ,
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a value in the range [\-1,\ 1].
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If
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.I x
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is a NaN, a NaN is returned.
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If
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.I x
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is +0 (\-0), +0 (\-0) is returned.
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If
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.I x
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is positive infinity (negative infinity),
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+1 (\-1) is returned.
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If
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.I x
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is subnormal,
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a range error occurs,
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and the return value is 2*x/sqrt(pi).
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.SH ERRORS
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See
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.BR math_error (7)
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for information on how to determine whether an error has occurred
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when calling these functions.
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.PP
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The following errors can occur:
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.TP
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Range error: result underflow (\fIx\fP is subnormal)
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.\" .I errno
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.\" is set to
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.\" .BR ERANGE .
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An underflow floating-point exception
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.RB ( FE_UNDERFLOW )
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is raised.
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.PP
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These functions do not set
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.IR errno .
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.\" FIXME . Is it intentional that these functions do not set errno?
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.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6785
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.SH "CONFORMING TO"
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C99, POSIX.1-2001.
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The variant returning
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.I double
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also conforms to
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SVr4, 4.3BSD.
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.SH "SEE ALSO"
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.BR cerf (3),
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.BR erfc (3),
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.BR exp (3)
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